Summary of development work
Rather than trying to visually compare inlet ports, we found it best to compare by measuring capacity with valve fitted in cc's using a burette, several engines that were down for power were found to be smaller capacity; 136cc instead of 148cc on an A7 twin, a B34 GS port 117cc extension 128 total induction 245cc.
All bench tests were carried out in uniform manner starting at lowest practical RPM and going up in increments of 250 RPM with no pause. Flash readings were never reported. We did try running power curves in reverse order starting at maximum revs and coming down but decided this gave false high readings.
Sandilands discovered almost by accident that a venturi shape after the carburettor can be 85% of the area of the carburettor body area with no loss of power, in fact it gave a small increase. We did most of our power curves with a flow meter hooked up between fuel tank and carburettor, this gives a valuable check on efficiency and also on correct carburettor settings.
When using two into one exhaust system it is desirable to have each pipe from the cylinder head to the junction of equal length if not carburation may be drastically affected at some point in the range. The way to avoid this problem is to ensure that each pipe has the same length to area ratio, in other words the longer piece will be larger diameter. In our experiments with the short stroke 500cc A7 twin we also found the angle of the two pipes at their intersection was important. I was at MIRA once waiting to use the timing strip whilst a group of Royal Enfield people tried to get the carburation right on one of the 700cc twins fitted with a two into one exhaust system, I noticed they were using the same diameter exhaust pipes of different lengths before the junction. Strangely enough this same rule holds good for induction pipes as found by Guzzi on their later single cylinder racers.
The A7 and A10 connecting rod bolts were originally BSF threads, we changed this to 26 threads per inch cycle threads as we thought larger area at the root of the thread would make a stronger bolt, we had to reduce torque when tightening the big end nuts proportionally, unfortunately someone in the drawing office forgot to tell the engine assembly and several bolts were broken before the error was discovered. Even more strange was the fact the broken bolts only happened to one of the several mechanics assembling the crank assemblies. I was asked to investigate, so sent Arthur Butler up to the engine assembly to watch how they did this torquing up. He returned a little later laughing with a small tobacco tin in his hand, It had plumbers tallow in it, apparently only one mechanic was putting tallow on the threads before tightening, with the results that nuts tightened appreciably more before the torque wrench recorded the correct torque figures. We accordingly tested some bolts with various lubricants on the thread and decided that important bolts such as connecting rod bolts should be assembled clean.
Oil Pumps.The BSA gear type pump is very simple and reliable, at one time we did some tests by simply running a pump on a drill press in a can of oil and measuring the temperature of the oil, we were surprised at how quickly the temperature rose especially as there was not resistance to the flow. On examination of the pump we decided that some oil was being compressed between the two gears, accordingly a small bypass was cut in the cover plate allowing oil to feed back to the inlet side of the pump. Further testing showed practically no heat build up in the oil. Some tests were carried out on A7 (using various viscosity oils, starting with 50 wt and coming down to 40 wt to 30 wt, 20 wt SAE 10 and finally 5 wt. We discovered that normal oil pressure was maintained on the SAE 10 50 wt, 40 wt and 30 wt. At SAE 20 viscosity pressure tended to drop particularly when hot. The engine was stripped at this point to see if the low pressure caused any bearing problems, everything looked pretty good. At SAE 10 wt pressure seemed very low in fact when hot was nil a further examination of the bearings and pistons showed no sign of trouble but the cam followers did not look too happy, starting to score.
A final run was made with SAE 5 wt pressure almost nil when cold, showed nil when hot especially when engine was revved up, finally the timing side main bearing failed. On stripping the engine we found the white metal had melted and run, but no trace of it in the oil or crankcase, when the sealing plugs were removed from the crankshaft the white metal, was found to be inside the oil passages of the crankshaft, the connecting rod bearings appeared to be in good condition. Apparently the light 5 wt oil was thrown outwards to the big end bearings by centrifugal force enough to lubricate the big end bearings adequately but in such quantity that it robbed oil from the main bearings faster than the oil pump could replace it.
One interesting test was when we set up a A10 engine and gearbox unit on the test bed driving the dyno by a short chain, the object was to try and measure the power loss in the gearbox in each gear. We could not measure the power in 1st gear as the dyno was turning too slowly to absorb the considerable torque due to the low gear ratio. As we expected the most efficient gear was 4th, the direct gear.
Surprisingly, 2nd gear was more efficient than 3rd gear due presumably to the fact that 2nd gear wheels were better supported than 3rd. The final part of the test was when we removed the gearbox and clutch and tried to run a fairly long chain from the engine to the dyno direct to see what difference was with gearbox out of action. To our surprise it could not be done, this rather long chain just whipped and banged and would not transmit power. We had to move the engine back on the block and used a short chain. Incidentally the power loss in 3rd gear was about 10% with about 8% loss in 2nd gear as compared with 4th gear with only 2%. One of the lesser known advantages of the eccentric rocker spindles is the ability to adjust the valves whilst the engine is running.
I suggested this to Reg Wilkes one day, however, he did not seem very keen to stand astride a high revving engine with a wrench in either hand so I appointed myself as the rocker manipulator. We started off on the 500 Gold Star race engine at about 5000 rpm with me firmly astride and adjusted each rocker until the maximum power reading was obtained. The engine was then blown cool with the fan and clearance checked, the inlet figure was something like .009" and exhaust a little more. Then the engine was run at 6000rpm and again rockers adjusted for maximum power and cooled down to room temperature and clearances checked, this time the inlet was .006" and exhaust .008".
Next a reading was taken at 6500 rpm and again clearances checked when cool. Now the inlet clearance was down to about .003" and exhaust .006", subsequent checks were made at 7000 rpm and 7500, with some pointed remarks made about what happened to me if the engine shuld blow up while I am astride it. The results at 7000 rpm were clearances Inlet .001" Exhaust .004" at 7500 rpm inlet nil, exhaust clearances .003". These were not exact figures (my memory is not that good) but the general trend was there at the higher revolutions the rockers and push rods were bending and whipping slightly.
Prior to these tests we had always set valve clearances with a cold engine, with inlet push rod just free to rotate and .003" clearance on the exhaust. The normal practice with regard to rocker angle in relation to valve stem has been to arrange for the rocker to be at right angles to the valve stem at half lift, the object being to minimise side thrust and cut down on valve guide wear. In the course of experiments with both the C12 and the A7 engine better running at high revolutions could be obtained when the rocker was at right angles to the valve stem at about l/32"to 1/16" lift. It was thought that this arrangement aligned the valve seat with the valve seat in the head just as the valve was closing, whereas with the common setting at half lift, the rocker side thrust will tip the valve slightly in the guide when seating and will have to realign itself as it seats. At very high revolutions there is not enough time for this and some efficiency will be lost. On the C12 this was visible even by turning the engine by hand, by inserting some packing between the rocker mounts and the head we were able to see the improved action. It is quite possible that most overhead valve engines using rockers could benefit from this rearrangement of rocker angles.
One unexpected results when trying a much larger and stiffer crankpin with plain bearing was considerable difficulty in lining up the flywheel assembly, presumably the wider shoulders made the assembly more rigid. Engine gaskets between rocker box and cylinder head usually made of paper were replaced with metal corrugated gaskets, these could be used over and over again and sealed better.
During the five years I was at BSA doing engine development I was fortunate in attracting some very bright and enthusiastic mechanics and apprentices, they all contributed to the progress we made with development of the BSA range. There was tendency to specialise but most could handle anything that came in the shop. Jimmy Gibbard did most of the odd machinery jobs, Jack Turner did the intricate inlet port arrangements and exploited the extra down draft angles and straight ports. Reg Wilkes, Bert Hole, Arthur Butler, Arthur Bridgewood, Bill Bently and Alan Sandilands could handle any aspect of engine building , the apprentices who spent more than average time with us were Gordon Smith, Robert Trigg, Ray Beech, David Harris and John Taft. Albert Dyde, ??? Harrison Ward and Hill came into the shop later. We also had some colonials like Barry Stormont and Cohn Mather during the winter months. I learned a great deal and was able to try out many ideas that I could never have done in the ordinary way, for this I am grateful to Mr Hopwood and BSA for this opportunity.
One of the chief abilities necessary in this type of work is to be able to 'sell' ideas to the Management, something I was not very good at. Thanks to BSA sending me to the USA on business trips I decided to emigrate and have had an interesting life in USA becoming a citizen in 1982, finally having my own business and a and a decent workshop including a dynomometer. I have not lost interest in motorcycles and at 75 own a 250cc Kawasaki 'Ninja', a remarkable little machine with a performance in road trim better than my old racers. We still enjoy trips to Road Atlanta to watch the motor cycle road each year.
Showing posts with label Reg Wilkes. Show all posts
Showing posts with label Reg Wilkes. Show all posts
Monday, 9 February 2009
Sunday, 25 January 2009
Roland Pike Autobiography - Chapter 23
The development of my favourite the Gold Star.
When I came to work at BSA in 1952 there was no programme of development for the Gold Star, at that time we seemed to just pick up problems as they developed and try to fix them. The 350 Gold Star did quite well in the Clubmans TT, their power output averaged 27 to 28bhp. There were a number of problems causing retirements in the races the most serious of these was the heads burning near the joint face. Cyril Halliburn who was my assistant in those days suggested it was the porous castings and wanted to blame the foundry, strangely, the foundry did not deny this but said they did not understand what was wrong. In the Isle of Man during the practice period several of the heads were discovered to be 'burnt' when removed for examination. My opinion was that the joint at the Back to top of the cylinder barrel and head left an annular gap varying from .005" to .035", the wider joints trapped some gas which detonated causing the burnt heads. The normal gasket was a fairly thick copper asbestos affair, the production people claimed an inability to hold tolerances on cylinder barrel spigot and cylinder head spigot joint to less than .015", the gaskets also varied in thickness. It must be remembered that this gasket also had to make an oil tight joint at push rod tunnel. My solution was to use a ‘Plexseal’ joint, this gasket was formed of aluminium foil .002" thick stuck together to form a laminated gasket whose thickness could be varied by peeling off a layer one at a time to get a perfect joint, keeping the annular joint gap to between zero and .002" and yet still sealing the push rod tunnel. My suggestion was accepted but it did not reach production until later in 1952 or early 1953.
Another quite serious problem was the crankcase breather, situated in the timing case. A small pen steel disc acted as an automatic flap valve, unfortunately it did not work efficiently if at all at high speeds, thus allowing a lot of engine oil to blow out of the crankcase. Some of the riders ran out of oil due to this, all complained of the oil all over the rear tyre. My solution was to build a rotating sleeve in the timing cover driven by a peg on the magneto pinion, this was made in time for our testing at Montlhery in 1953. This mechanical breather was very successful as it kept the pressure in the crankcase about 4" - 7" below atmosphere at all speeds, which kept the oil in the engine and rear tire cleaner. Surprisingly this breather contributed a slight increase in power of 4bhp over the flap valve. The best timing was for the port to open 20 degrees before BDC on each stroke. Another problem was the occasional exhaust valve breakage which usually did quite a bit of damage.
The Research dept came up with the answer here. A special nickel alloy Nimonic 80, after its use I never saw another one break. A difficult problem was valve springs. I would have liked to have gone to hairpin springs but this was not possible. We tried all the usual approaches, talking to Terry's, the spring experts, even our friends at Rover designed a spring to try, our own spring shop tried various tricks and materials but we were getting very little progress, then Hap Alzina sent some S&W springs for the twins, I decided to try these in a Gold Star and they worked beautifully right from the start, giving us a big increase in maximum revs. I suspected shorter connecting rods might show some advantages in several ways, firstly by changing piston motion relative to crankshaft rotation, also shortening the whole engine including the push rods.. We built some 350 engines using A10 and A7 connecting rods, these showed an appreciable increase in performance but we could not be sure what was due to the shorter connecting roads or the fact that they were lighter and had plain bearing big ends. Mr Hopwood agreed to have some special forgings made up using the shorter dimensions, this enabled us to carry out some direct comparisons which showed that we had got a small increase in power through the lighter alloy rods and plain bearing, but that a worth while increase came from the shorter length rod.
These tests became useful later on when we wanted to find out whether a one-piece crankshaft offered any advantages over the built- up flywheel assembly. It showed excellent results especially at high revs, the only problem experienced with one-piece crankshaft was the connecting rod detachable bearing cap. It is very difficult to make a connecting rod with a detachable cap as strong as the one-piece rod. These 1952 Gold Stars had push rods made of solid dural with steel caps rivetted on. We substituted some 3/8 dia T4 tubing with lighter end caps pressed on. You can imagine how much lighter these were. I made, a sketch of a rocker spindle which had the rocker bearing portion machined eccentrically and the Drawing office made an official drawing and we were able to eliminate the heavy valve adjuster that kept the oil in the engine and rear tyre cleaner. Surprisingly this breather contributed a slight increase in power .4bhp over the flap valve. The best timing was for the port to open 20 degrees before BDC on each stroke. Another problem was the occasional exhaust valve breakage which usually did quite a bit of damage
The lower half of the Gold Star engine was basically similar to the 1938 M24 Gold Star and to the B33 post-war iron 500, although the crankpin assembly was changed quite a lot, the flywheels were always forged steel. The pre-war and the immediate post-war ZB Gold. Star differed quite a lot, including having bore and stroke changes. I liked the non-detachable rocker box of the ZB, even though it was a bit of a fiddle getting the head off with the engine in the frame. This earlier design avoided the oil leaks that later Gold Stars sometimes experienced at the rocker box joints. The later big fin Gold Star engine which I suppose is the version most beloved by enthusiasts, came about in the following way. After all the debacles we had been having with the twins some of which I have described, it was decided that as we were making a new cylinder head for the 350 Gold Star, we could afford a 500 version of it. Brian Jones of the Drawing office, a very capable and gifted young fellow, set about designing the new head. Mr Hopwood told him to consult with me on it so every day I would confer with him his office, look over his shoulder and make a few suggestions. He was decent enough to incorporate some of them.
One of my ideas was that of sloping the fins between the two rocker box joints to get an air flow across the dead space on Back to top of the head. Of course we did not know what the air would do but it worked well in practice. I am always a little skeptical about the air flow paths around a motor cycle cylinder head particularly when mounted in the frame. The new big fin heads both 350 and 500 had a cooling fin area of about 520 square inches. We measured it by getting an apprentice to cut out pieces of squared paper to match all the fins then laboriously compute their combined areas. We were.of the opinion that 520 square inches should be just adequate for the 500 version and possibly over generous for the 350. I do not think that at that time we visualised using one of these heads on a 250. Some interim heads for 1954 Daytona models were made by using 350 castings machined to suit 500, these gave more power than the normal 500 heads due to better down draft inlet ports and slightly more fin area. Of course they were a bit thin in places and tended to crack. The new heads were ready for the 1954 TT and were an instant success, and by using larger inlet valves the 350 power was increased from about 30 to 33-34bhp'.
The timed breather was also used and the eccentric rocker spindle and Nimonic 80 exhaust valves. The improved valve springs and the laminated head gaskets all contributed to a most reliable engine. The 500cc version gave over 44bhp in IOM trim. These engines all had the shorter connecting rods, the 500 had oval flywheels to get piston skirt clearance and still have some flywheel effect this later however proved to be unnecessary. During all this activity on Gold Stars many other developments were going on. We tended to let the mechanics specialize as they seemed to be more efficient in this way. Reg Wilkes for example did most Gold Star development, Arthur Butler worked on A7 and A10 development. Arthur Bridgewood worked on the 500cc overhead cam twins and the MC4. Bill Bently exclusive on MC1. Bert Hole worked on the twins . Alan Sandilands did some work on the MC1 and a lot of special projects like a scrambler C12, special short stroke engines with one piece crankshafts. Jimmy Gibbard spent his time as a machinist making special parts for the shop. Jake Turner came in later as both machinist and mechanic and did a lot of work on 250 Gold Stars, was also responsible for machining the straight port head for 350 Gold Star. All of them at some time or another worked on the 'experiments to find optimum bore and stroke dimensions. We did some experimenting with chrome plated cylinders which was promising but inconclusive.
Due to the temporary shortage of aluminium because of; the Korean War some Gold Star cylinders were, cast iron, we were instructed to evaluate these in case the factory was forced to use them. They were terribly heavy, about three times the weight of the standard alloy cylinder. Much to everyone’s amazement we got slightly more power and no overheating, the piston rings also appeared to run better in the iron cylinder, which set me thinking. When the original tests were completed we knocked all the fins off the iron cylinder and turned it down to a heavy sleeve in the lathe,, then bored a standard Gold Star cylinder jacket to be just a bit smaller than the outside of the iron sleeve. The alloy jacket was, heated up and dropped on, making a nice tight fit, a flange had been left at the bottom of the line to sit on crankcase face. As the line's had been left about *" thick, the Back to top of it made a good seat for the cylinder head. Due to all the machining and shrinking process the bore had distorted slightly and the rings did not bed in very well, so we had it lightly ground true which left it about .002" oversize.
On test it performed very well, more power, better oil control and no scuff marks as we got with the standard austenitic liners. I discussed this with 'Brico' the piston ring people and they said they were not surprised and agreed to make us two special thick sleeves for further testing, one using the austenitic material and one plain cast iron. We gave these extensive testing, the rings bedded better and controlled oil consumption better with an iron sleeve. The tests were repeated with 350 Gold Star, again the plain cast iron showed up to advantage.
The Design office were interested but reluctant to admit that austenitic was not necessary. They changed to the thicker liner in production, but I am not sure whether they changed the material. Early in 1953 we tested some chrome plated Back to top compression rings from Brico in a special 350 Gold Star we had built for Charlie Salt. This engine had what was then the new eccentric rockers, a plain big end bearing in an alloy con rod. This engine was in the 350 Gold Star we had taken to Montlhery for high speed testing. It performed very well but the chrome ring even after hours of running never really bedded in. We reported this to Brico and they said not to worry as they were grinding these rings with a slight taper degree on the face, and that we should find them ok. After trying these new taper face rings we found them very much better and ultimately got almost 34bhp from this engine. Unfortunately the connecting rod cap broke up in the Junior TT due to the self locking nuts coming loose.
Following a hot tip I had received, we built a 350 Gold Star with cylinder axis offset 3/8" to the rear, this gives a peculiar motion to the piston, with the effect of a short connecting rod 4 3/4" long and 8" long going down and 1.4 increase in bhp, but it was a rough engine. Due to the good results I had had using a dural (RR56) connecting rod with plain connecting rod bearing in my Rudges I wanted to try this in a Gold Star. We had made a connecting rod of this type, made to my drawings, it turned out to be reliable and smooth but very little more power than the standard steel rod. We used this engine for comparison tests of various parts and ideas for several years. It was finally sold for scrap when I left BSA Quite a bit of testing was of moulded bakelite big end bearing cages, as they would have been a lot cheaper to produce than the dural cages used in production, but they failed at high RPM.
The original Gold Star BSA got its name by lapping Brooklands race track at over 100mph in 1938 ridden by Wal Handley, a very fine rider. This was followed in 1939 by an alloy engine version called a Gold Star, it had 82 x 94 bore and stroke. In 1954 we made a modern version of this engine to see if the longer stroke showed any advantages, using M20 flywheels, a pre war piston and modern cylinder sleeved down to 82 mm. It was a disappointment as it did not pull any better and gave 42bhp. Charlie Salt & I rode it around Oulton Park. It was also tested as a scrambler by Dennis Hardwick and someone in the Competition department. After a final strip down and rebuild we got 4bhp which wasn’t bad but at the time the standard 500 Gold Star was giving 45-46 quite readily and as much as 50bhp as flash readings. We made a range of 350 engines with bore and stroke ratios varying from 63 x 112 to 71 x 88 and 76 x 76, 8.x 66 and 85 x 61.5.
Not all at once but fitted in with other testing, the 82 x 66 engine was built in two forms both used one piece crankshaft plain big end bearings and outside flywheels. The first engine had a higher compression ratio and orthodox intake port merely straightened and given a little more downdraft. The best reading on this engine was 38~bhp, but one day it seized up so suddenly that the flywheel inertia twisted the crankshaft making it impossible to strip. The next version had bigger diameter mainshaft and lower compression ratio, due to unavailability of the pre-war Gold Star piston we had been using, this engine was very reliable and we did all sorts of tests using various carburettors, silencers and cams.
The best power with racing set up was 36bhp at 7250 RPM and 36.1 at 7750 RPM. The most interesting was the power obtained with road cams and silencer and monobloc carburettor 27.3 at 7000 and still pulled strongly at 2500 RPM. From these test in 1953-54-55 I became convinced that short strokes were the way to go. Modern 1988 motor cycles would seem to bear this out. The Gold Star head gasket joint system is rather unique and merits some comment, the push rod tunnel construction called for something other than the classic four stud joint to prevent oil leaks. The system adopted consisted of four long studs coming up from the crankcase in orthodox fashion, plus four more short bolts that simply united barrel and head from below, one bolt in the push rod tunnel the others at front and rear and on the left side. All eight bolts screwed into bronze inserts which are themselves screwed into the head casting. The system was not completely successful as we sometimes got leaky joints. Another snag was the difficulty in tightening the rear bolt, sometimes it was necessary to remove the magneto in order to get at this bolt, so we often left them out with no ill effects. At one time we went to only five fixtures, with no problems. on our special engines we adopted the final variation on these themes by making four hollow steel tubes to replace the crankcase studs and ran four bolts down from the head into the internal threads in the four tubes, which had external threads at their lower ends where this four bolt arrangement was fully proof against gasket blowing and greatly simplified head removal, especially with the engine in the frame. This last system would have been cheaper, but in spite of this was not adopted.
Connecting rod breakage used to be a frequent Back to topic of conversation amongst racing men as breaking at high speed can lead to some terrifying moments, besides doing a lot of damage. I believe the forged steel rods in BSA engines were outstandingly good. A number of Manx Norton riders I know used them because they found them more reliable than some of their original equipment. BSA had a great deal of know-how when it came to forging. No one else in the motor cycle industry forged their own connecting rods, other makes had to go to outside supplies like Laystall or Garrington. Naturally when you make parts yourself you have more control and you can try different components. We were lucky in that we had a good smithy and good people working in it.
About the time Lucas came out with a new racing magneto of the rotating magnet type, it was supposed to be less affected by vibration and more reliable but I was not very, impressed with its performance, it also had less range of advance, and retard. Personally I preferred the BTH magneto. We borrowed a 350 Manx Norton engine in 1956 which had a good power curve, we got 38bhp and very good torque with it, rather better than our own engines. On examining the cams we found that due to being a double overhead camshaft design there was very low reciprocating weight, enabling very quick lifts to be used without very 'long' timing. This particular Norton was a square engine 76 x 76 with squish piston. We built a Gold Star engine to these dimensions to test the so called squish effect using a Norton piston in a modified BSA head, this gave us 36.4bhp but we could get practically the same power with ordinary non-squish combustion chamber, maybe it only works with higher compression ratios, ours was 9.0: 1
The quality of mechanics who were employed in development was very high, there was not much they could not do. Alan Sandilands once made some prototype cams by hand. Jake Turner was a terrific machinist, very fast and accurate, he also thought up the method of making a virtually straight inlet port. Reg Wilkes was the artist who would fettle a piston and head until he got the maximum power that was possible.
We made some alloy tappets that were very light and worked very well, they seemed to be very compatible with the hard steel cams, the only problem was after about 500 racing miles they broke, but while they worked they were good. I feel sure that if we had been able to make larger diameter guides and stems to suit they would have been very satisfactory. Charlie Salt once set out to design a new crankcase for the Gold Star using a high camshaft, but it had to look like a BSA he was told. Sunbeam and Rudge had both made high camshaft engines pre-war with chain driven camshafts.
At various times we had problems with A10 and A7 connecting rods especially when used in the plain bearing Gold Star. We were trying to get away from split pins and castellated nuts and trying various patent self-locking nuts. The only one that was successful was the pinnacle nut which had a steel diaphragm to lock the nut. One of my ambitions was to utilise all the successful ideas we had used on the Gold Star and make them standard parts so that the B31 and B33 would use .the same connecting rods and valve sizes, push rods made of tubular alloy instead of solid, eccentric rocker spindles and the simple Gold Star rocker, but still retaining the iron heads and cylinder barrels. Unfortunately the production people could not see the benefit of these ideas. We did extensive testing with floating bush big end bearings mostly in the 500 Gold Star on the basis that if it stood full power and revs in that, it would certainly last in a lower power engine. The floating bushes were very much cheaper to make. During road testing at MIRA. Barry Stormont did 116 miles in the hour which was something of a record for us. It was in winter time and he was literally frozen stiff, we had to take him out to a warm cafe to thaw him out.
All through a long test programme, using factory bushes made by Glacier bearings we had no trouble, but when we started using their production samples they were almost useless, so we had to F->rop the whole scheme, which was a pity. We also tried a large diameter wrapped bush running on a large crankpin, we tried both bi-metal and copper lead, they were both satisfactory, but the larger crankpin was so rigid we had trouble aligning the flywheels. All these plain bearings really need a large paper filter built in to the engine, but all we had was a small tecalemit filter on the return oil line. Although either of these bearings would have shown a big economy I did not receive much encouragement. I think the factory was scared to make a change, although they already had these plain bearings in the twins during testing of the floating bush connecting rod bearing we had problems with over oiling. It appeared that too much' oil was being thrown up to the cylinder and piston, this we corrected by reducing the diameter of the flywheels and chamfering them.
The following summary of the development of the Gold Stars may be of interest.
1952 350cc
27 - 28bhp
1956 350cc
35 - 36bhp
1952 500cc
35 - 37bhp
1956 500cc
44 - 46bhp
We felt that these increases came from higher revs which in turn came from lighter valve gear, better springs, larger carburettors, higher compression with cooler running due to the big fin heads plus higher octane fuel. About 1955 the desire developed for a better brake for our scramblers. Since the management wanted to avoid spending money, as usual it was decided one brake would have to do for both Clubmans TT and racing Gold Stars-and Scramblers. Dennis Hardwick wanted a small intake for the scramblers, Charlie Salt and I wanted a big brake for the Clubman. We compromised on a 19O mm brake on Charlie’s suggestion, who told me he was banking on a belief that Hardwick would not know how big 190mm really was. As it turned out Hardwick didn’t. So we came out with this fairly large brake, with wide shoes which was used for some years afterwards although in my opinion it was not as good as the earlier cast iron drum with ribs around it. That was the best Gold Star brake. Charlie did not like it himself and he blamed Hardwick for the fact that it was too small as he would have preferred 200mm diameter. The l90 mm brake was designed by Charlie and it turned out to be rather heavy for its size.
When I came to work at BSA in 1952 there was no programme of development for the Gold Star, at that time we seemed to just pick up problems as they developed and try to fix them. The 350 Gold Star did quite well in the Clubmans TT, their power output averaged 27 to 28bhp. There were a number of problems causing retirements in the races the most serious of these was the heads burning near the joint face. Cyril Halliburn who was my assistant in those days suggested it was the porous castings and wanted to blame the foundry, strangely, the foundry did not deny this but said they did not understand what was wrong. In the Isle of Man during the practice period several of the heads were discovered to be 'burnt' when removed for examination. My opinion was that the joint at the Back to top of the cylinder barrel and head left an annular gap varying from .005" to .035", the wider joints trapped some gas which detonated causing the burnt heads. The normal gasket was a fairly thick copper asbestos affair, the production people claimed an inability to hold tolerances on cylinder barrel spigot and cylinder head spigot joint to less than .015", the gaskets also varied in thickness. It must be remembered that this gasket also had to make an oil tight joint at push rod tunnel. My solution was to use a ‘Plexseal’ joint, this gasket was formed of aluminium foil .002" thick stuck together to form a laminated gasket whose thickness could be varied by peeling off a layer one at a time to get a perfect joint, keeping the annular joint gap to between zero and .002" and yet still sealing the push rod tunnel. My suggestion was accepted but it did not reach production until later in 1952 or early 1953.
Another quite serious problem was the crankcase breather, situated in the timing case. A small pen steel disc acted as an automatic flap valve, unfortunately it did not work efficiently if at all at high speeds, thus allowing a lot of engine oil to blow out of the crankcase. Some of the riders ran out of oil due to this, all complained of the oil all over the rear tyre. My solution was to build a rotating sleeve in the timing cover driven by a peg on the magneto pinion, this was made in time for our testing at Montlhery in 1953. This mechanical breather was very successful as it kept the pressure in the crankcase about 4" - 7" below atmosphere at all speeds, which kept the oil in the engine and rear tire cleaner. Surprisingly this breather contributed a slight increase in power of 4bhp over the flap valve. The best timing was for the port to open 20 degrees before BDC on each stroke. Another problem was the occasional exhaust valve breakage which usually did quite a bit of damage.
The Research dept came up with the answer here. A special nickel alloy Nimonic 80, after its use I never saw another one break. A difficult problem was valve springs. I would have liked to have gone to hairpin springs but this was not possible. We tried all the usual approaches, talking to Terry's, the spring experts, even our friends at Rover designed a spring to try, our own spring shop tried various tricks and materials but we were getting very little progress, then Hap Alzina sent some S&W springs for the twins, I decided to try these in a Gold Star and they worked beautifully right from the start, giving us a big increase in maximum revs. I suspected shorter connecting rods might show some advantages in several ways, firstly by changing piston motion relative to crankshaft rotation, also shortening the whole engine including the push rods.. We built some 350 engines using A10 and A7 connecting rods, these showed an appreciable increase in performance but we could not be sure what was due to the shorter connecting roads or the fact that they were lighter and had plain bearing big ends. Mr Hopwood agreed to have some special forgings made up using the shorter dimensions, this enabled us to carry out some direct comparisons which showed that we had got a small increase in power through the lighter alloy rods and plain bearing, but that a worth while increase came from the shorter length rod.
These tests became useful later on when we wanted to find out whether a one-piece crankshaft offered any advantages over the built- up flywheel assembly. It showed excellent results especially at high revs, the only problem experienced with one-piece crankshaft was the connecting rod detachable bearing cap. It is very difficult to make a connecting rod with a detachable cap as strong as the one-piece rod. These 1952 Gold Stars had push rods made of solid dural with steel caps rivetted on. We substituted some 3/8 dia T4 tubing with lighter end caps pressed on. You can imagine how much lighter these were. I made, a sketch of a rocker spindle which had the rocker bearing portion machined eccentrically and the Drawing office made an official drawing and we were able to eliminate the heavy valve adjuster that kept the oil in the engine and rear tyre cleaner. Surprisingly this breather contributed a slight increase in power .4bhp over the flap valve. The best timing was for the port to open 20 degrees before BDC on each stroke. Another problem was the occasional exhaust valve breakage which usually did quite a bit of damage
The lower half of the Gold Star engine was basically similar to the 1938 M24 Gold Star and to the B33 post-war iron 500, although the crankpin assembly was changed quite a lot, the flywheels were always forged steel. The pre-war and the immediate post-war ZB Gold. Star differed quite a lot, including having bore and stroke changes. I liked the non-detachable rocker box of the ZB, even though it was a bit of a fiddle getting the head off with the engine in the frame. This earlier design avoided the oil leaks that later Gold Stars sometimes experienced at the rocker box joints. The later big fin Gold Star engine which I suppose is the version most beloved by enthusiasts, came about in the following way. After all the debacles we had been having with the twins some of which I have described, it was decided that as we were making a new cylinder head for the 350 Gold Star, we could afford a 500 version of it. Brian Jones of the Drawing office, a very capable and gifted young fellow, set about designing the new head. Mr Hopwood told him to consult with me on it so every day I would confer with him his office, look over his shoulder and make a few suggestions. He was decent enough to incorporate some of them.
One of my ideas was that of sloping the fins between the two rocker box joints to get an air flow across the dead space on Back to top of the head. Of course we did not know what the air would do but it worked well in practice. I am always a little skeptical about the air flow paths around a motor cycle cylinder head particularly when mounted in the frame. The new big fin heads both 350 and 500 had a cooling fin area of about 520 square inches. We measured it by getting an apprentice to cut out pieces of squared paper to match all the fins then laboriously compute their combined areas. We were.of the opinion that 520 square inches should be just adequate for the 500 version and possibly over generous for the 350. I do not think that at that time we visualised using one of these heads on a 250. Some interim heads for 1954 Daytona models were made by using 350 castings machined to suit 500, these gave more power than the normal 500 heads due to better down draft inlet ports and slightly more fin area. Of course they were a bit thin in places and tended to crack. The new heads were ready for the 1954 TT and were an instant success, and by using larger inlet valves the 350 power was increased from about 30 to 33-34bhp'.
The timed breather was also used and the eccentric rocker spindle and Nimonic 80 exhaust valves. The improved valve springs and the laminated head gaskets all contributed to a most reliable engine. The 500cc version gave over 44bhp in IOM trim. These engines all had the shorter connecting rods, the 500 had oval flywheels to get piston skirt clearance and still have some flywheel effect this later however proved to be unnecessary. During all this activity on Gold Stars many other developments were going on. We tended to let the mechanics specialize as they seemed to be more efficient in this way. Reg Wilkes for example did most Gold Star development, Arthur Butler worked on A7 and A10 development. Arthur Bridgewood worked on the 500cc overhead cam twins and the MC4. Bill Bently exclusive on MC1. Bert Hole worked on the twins . Alan Sandilands did some work on the MC1 and a lot of special projects like a scrambler C12, special short stroke engines with one piece crankshafts. Jimmy Gibbard spent his time as a machinist making special parts for the shop. Jake Turner came in later as both machinist and mechanic and did a lot of work on 250 Gold Stars, was also responsible for machining the straight port head for 350 Gold Star. All of them at some time or another worked on the 'experiments to find optimum bore and stroke dimensions. We did some experimenting with chrome plated cylinders which was promising but inconclusive.
Due to the temporary shortage of aluminium because of; the Korean War some Gold Star cylinders were, cast iron, we were instructed to evaluate these in case the factory was forced to use them. They were terribly heavy, about three times the weight of the standard alloy cylinder. Much to everyone’s amazement we got slightly more power and no overheating, the piston rings also appeared to run better in the iron cylinder, which set me thinking. When the original tests were completed we knocked all the fins off the iron cylinder and turned it down to a heavy sleeve in the lathe,, then bored a standard Gold Star cylinder jacket to be just a bit smaller than the outside of the iron sleeve. The alloy jacket was, heated up and dropped on, making a nice tight fit, a flange had been left at the bottom of the line to sit on crankcase face. As the line's had been left about *" thick, the Back to top of it made a good seat for the cylinder head. Due to all the machining and shrinking process the bore had distorted slightly and the rings did not bed in very well, so we had it lightly ground true which left it about .002" oversize.
On test it performed very well, more power, better oil control and no scuff marks as we got with the standard austenitic liners. I discussed this with 'Brico' the piston ring people and they said they were not surprised and agreed to make us two special thick sleeves for further testing, one using the austenitic material and one plain cast iron. We gave these extensive testing, the rings bedded better and controlled oil consumption better with an iron sleeve. The tests were repeated with 350 Gold Star, again the plain cast iron showed up to advantage.
The Design office were interested but reluctant to admit that austenitic was not necessary. They changed to the thicker liner in production, but I am not sure whether they changed the material. Early in 1953 we tested some chrome plated Back to top compression rings from Brico in a special 350 Gold Star we had built for Charlie Salt. This engine had what was then the new eccentric rockers, a plain big end bearing in an alloy con rod. This engine was in the 350 Gold Star we had taken to Montlhery for high speed testing. It performed very well but the chrome ring even after hours of running never really bedded in. We reported this to Brico and they said not to worry as they were grinding these rings with a slight taper degree on the face, and that we should find them ok. After trying these new taper face rings we found them very much better and ultimately got almost 34bhp from this engine. Unfortunately the connecting rod cap broke up in the Junior TT due to the self locking nuts coming loose.
Following a hot tip I had received, we built a 350 Gold Star with cylinder axis offset 3/8" to the rear, this gives a peculiar motion to the piston, with the effect of a short connecting rod 4 3/4" long and 8" long going down and 1.4 increase in bhp, but it was a rough engine. Due to the good results I had had using a dural (RR56) connecting rod with plain connecting rod bearing in my Rudges I wanted to try this in a Gold Star. We had made a connecting rod of this type, made to my drawings, it turned out to be reliable and smooth but very little more power than the standard steel rod. We used this engine for comparison tests of various parts and ideas for several years. It was finally sold for scrap when I left BSA Quite a bit of testing was of moulded bakelite big end bearing cages, as they would have been a lot cheaper to produce than the dural cages used in production, but they failed at high RPM.
The original Gold Star BSA got its name by lapping Brooklands race track at over 100mph in 1938 ridden by Wal Handley, a very fine rider. This was followed in 1939 by an alloy engine version called a Gold Star, it had 82 x 94 bore and stroke. In 1954 we made a modern version of this engine to see if the longer stroke showed any advantages, using M20 flywheels, a pre war piston and modern cylinder sleeved down to 82 mm. It was a disappointment as it did not pull any better and gave 42bhp. Charlie Salt & I rode it around Oulton Park. It was also tested as a scrambler by Dennis Hardwick and someone in the Competition department. After a final strip down and rebuild we got 4bhp which wasn’t bad but at the time the standard 500 Gold Star was giving 45-46 quite readily and as much as 50bhp as flash readings. We made a range of 350 engines with bore and stroke ratios varying from 63 x 112 to 71 x 88 and 76 x 76, 8.x 66 and 85 x 61.5.
Not all at once but fitted in with other testing, the 82 x 66 engine was built in two forms both used one piece crankshaft plain big end bearings and outside flywheels. The first engine had a higher compression ratio and orthodox intake port merely straightened and given a little more downdraft. The best reading on this engine was 38~bhp, but one day it seized up so suddenly that the flywheel inertia twisted the crankshaft making it impossible to strip. The next version had bigger diameter mainshaft and lower compression ratio, due to unavailability of the pre-war Gold Star piston we had been using, this engine was very reliable and we did all sorts of tests using various carburettors, silencers and cams.
The best power with racing set up was 36bhp at 7250 RPM and 36.1 at 7750 RPM. The most interesting was the power obtained with road cams and silencer and monobloc carburettor 27.3 at 7000 and still pulled strongly at 2500 RPM. From these test in 1953-54-55 I became convinced that short strokes were the way to go. Modern 1988 motor cycles would seem to bear this out. The Gold Star head gasket joint system is rather unique and merits some comment, the push rod tunnel construction called for something other than the classic four stud joint to prevent oil leaks. The system adopted consisted of four long studs coming up from the crankcase in orthodox fashion, plus four more short bolts that simply united barrel and head from below, one bolt in the push rod tunnel the others at front and rear and on the left side. All eight bolts screwed into bronze inserts which are themselves screwed into the head casting. The system was not completely successful as we sometimes got leaky joints. Another snag was the difficulty in tightening the rear bolt, sometimes it was necessary to remove the magneto in order to get at this bolt, so we often left them out with no ill effects. At one time we went to only five fixtures, with no problems. on our special engines we adopted the final variation on these themes by making four hollow steel tubes to replace the crankcase studs and ran four bolts down from the head into the internal threads in the four tubes, which had external threads at their lower ends where this four bolt arrangement was fully proof against gasket blowing and greatly simplified head removal, especially with the engine in the frame. This last system would have been cheaper, but in spite of this was not adopted.
Connecting rod breakage used to be a frequent Back to topic of conversation amongst racing men as breaking at high speed can lead to some terrifying moments, besides doing a lot of damage. I believe the forged steel rods in BSA engines were outstandingly good. A number of Manx Norton riders I know used them because they found them more reliable than some of their original equipment. BSA had a great deal of know-how when it came to forging. No one else in the motor cycle industry forged their own connecting rods, other makes had to go to outside supplies like Laystall or Garrington. Naturally when you make parts yourself you have more control and you can try different components. We were lucky in that we had a good smithy and good people working in it.
About the time Lucas came out with a new racing magneto of the rotating magnet type, it was supposed to be less affected by vibration and more reliable but I was not very, impressed with its performance, it also had less range of advance, and retard. Personally I preferred the BTH magneto. We borrowed a 350 Manx Norton engine in 1956 which had a good power curve, we got 38bhp and very good torque with it, rather better than our own engines. On examining the cams we found that due to being a double overhead camshaft design there was very low reciprocating weight, enabling very quick lifts to be used without very 'long' timing. This particular Norton was a square engine 76 x 76 with squish piston. We built a Gold Star engine to these dimensions to test the so called squish effect using a Norton piston in a modified BSA head, this gave us 36.4bhp but we could get practically the same power with ordinary non-squish combustion chamber, maybe it only works with higher compression ratios, ours was 9.0: 1
The quality of mechanics who were employed in development was very high, there was not much they could not do. Alan Sandilands once made some prototype cams by hand. Jake Turner was a terrific machinist, very fast and accurate, he also thought up the method of making a virtually straight inlet port. Reg Wilkes was the artist who would fettle a piston and head until he got the maximum power that was possible.
We made some alloy tappets that were very light and worked very well, they seemed to be very compatible with the hard steel cams, the only problem was after about 500 racing miles they broke, but while they worked they were good. I feel sure that if we had been able to make larger diameter guides and stems to suit they would have been very satisfactory. Charlie Salt once set out to design a new crankcase for the Gold Star using a high camshaft, but it had to look like a BSA he was told. Sunbeam and Rudge had both made high camshaft engines pre-war with chain driven camshafts.
At various times we had problems with A10 and A7 connecting rods especially when used in the plain bearing Gold Star. We were trying to get away from split pins and castellated nuts and trying various patent self-locking nuts. The only one that was successful was the pinnacle nut which had a steel diaphragm to lock the nut. One of my ambitions was to utilise all the successful ideas we had used on the Gold Star and make them standard parts so that the B31 and B33 would use .the same connecting rods and valve sizes, push rods made of tubular alloy instead of solid, eccentric rocker spindles and the simple Gold Star rocker, but still retaining the iron heads and cylinder barrels. Unfortunately the production people could not see the benefit of these ideas. We did extensive testing with floating bush big end bearings mostly in the 500 Gold Star on the basis that if it stood full power and revs in that, it would certainly last in a lower power engine. The floating bushes were very much cheaper to make. During road testing at MIRA. Barry Stormont did 116 miles in the hour which was something of a record for us. It was in winter time and he was literally frozen stiff, we had to take him out to a warm cafe to thaw him out.
All through a long test programme, using factory bushes made by Glacier bearings we had no trouble, but when we started using their production samples they were almost useless, so we had to F->rop the whole scheme, which was a pity. We also tried a large diameter wrapped bush running on a large crankpin, we tried both bi-metal and copper lead, they were both satisfactory, but the larger crankpin was so rigid we had trouble aligning the flywheels. All these plain bearings really need a large paper filter built in to the engine, but all we had was a small tecalemit filter on the return oil line. Although either of these bearings would have shown a big economy I did not receive much encouragement. I think the factory was scared to make a change, although they already had these plain bearings in the twins during testing of the floating bush connecting rod bearing we had problems with over oiling. It appeared that too much' oil was being thrown up to the cylinder and piston, this we corrected by reducing the diameter of the flywheels and chamfering them.
The following summary of the development of the Gold Stars may be of interest.
1952 350cc
27 - 28bhp
1956 350cc
35 - 36bhp
1952 500cc
35 - 37bhp
1956 500cc
44 - 46bhp
We felt that these increases came from higher revs which in turn came from lighter valve gear, better springs, larger carburettors, higher compression with cooler running due to the big fin heads plus higher octane fuel. About 1955 the desire developed for a better brake for our scramblers. Since the management wanted to avoid spending money, as usual it was decided one brake would have to do for both Clubmans TT and racing Gold Stars-and Scramblers. Dennis Hardwick wanted a small intake for the scramblers, Charlie Salt and I wanted a big brake for the Clubman. We compromised on a 19O mm brake on Charlie’s suggestion, who told me he was banking on a belief that Hardwick would not know how big 190mm really was. As it turned out Hardwick didn’t. So we came out with this fairly large brake, with wide shoes which was used for some years afterwards although in my opinion it was not as good as the earlier cast iron drum with ribs around it. That was the best Gold Star brake. Charlie did not like it himself and he blamed Hardwick for the fact that it was too small as he would have preferred 200mm diameter. The l90 mm brake was designed by Charlie and it turned out to be rather heavy for its size.
Roland Pike Autobiography - Chapter 22
The Terrible Twins
I have never liked the air cooled vertical twin, but they looked neat, were simple, had an even firing, smooth exhaust note, fitting neatly into the same frame as their predecessors, the singles. The vibration was terrible, it seemed worse than the single, at least it was more noticeable. To my mind the head joint on all vertical twins with one-piece heads and cylinder block was marginal and subject to distortion. At BSA we must have done a fantastic amount of work on twins, judging by my notes. BSA had made up their minds that the twin was the motor cycle engine of the future. Every time I rode one it gave me the willies - the vibration was so noticeable. We tried all sorts of cures to get rid of the shakes and I still think our best ever effort in that direction was a short stroke 500 we made in 1953. Charlie Salt & I ran and ran it until we wore it out but no one seemed interested in it. This short stroke engine was a 500 A7 using a 650 head, barrel and pistons slightly modified. The crank was machined from the solid. This arrangement gave a 70 x 64.5 bore and stroke and instead of having a bolt on flywheel it had a triangular bob weight machined in the centre of the crank and discs next to the journal bearings. It was a very smooth running engine, both on the dyno and on the road. Power output was similar to the Star Twin, using 7.25:1 compression ratio.
With further tuning and lighter valve gear it gave 36bhp at 7000 a specially developed two into one exhaust system, we got as much as 39 horsepower at 7000. It was a most exciting machine to ride, as you accelerated it went on a normal power curve, then suddenly the exhaust note would change and it would 'yowl' right on up to maximum about 107mph Back in 1953 on low octane petrol this was quite an exciting performance on the road. Charlie and I enjoyed that engine.
The so-called Star Twin camshaft was a sporty one designed I think by Jack Amott although the design office never gave him credit for it. It was quite useable on the road with silencers fitted and also useful with open pipes. The fellows in my shop told me Jack did all the work on cams and I have no reason to doubt their words. Later on we went to the Daytona camshaft which was really a race cam and not very good at low revs but good at high speeds. Amott did design a racing cam for the twin, but we were unable to make it work properly, it was too radical and hard on valve springs. Reg Wilkes mentioned that if the drawing office had stuck to Jack’s original design they would have been all right. I asked to see Amott's original design and Reg got his camshaft out of a cabinet and showed it to me. It had a much larger base circle than the drawing office version, although to be quite honest I could not see what effect this would have. Wilkes suggested I try it sometime, he was sure it would work better and it did. It was still pretty radical. I never could understand why the drawing office decided to change the base circle diameter. One of the disadvantages of a larger base circle is a higher rubbing speed on the other hand you can get a smoother easier ???
Twin camshaft problems. Whilst working at BSA Dennis Lashmar carried on racing my old 'Pike BSA' with the alloy twin engine. I think he had one good win on a wet day at Snetterton, when it ran cool enough not to blow up. Latterly whenever we went to Silverstone or anywhere to watch him, he finished up sliding along on his backside at about 100mph with a broken crankshaft. This was too dangerous I considered. Once just after the massed start at Silverstone, with the pack all bunched up and approaching Woodcote corner at over 100mph the Beesa suddenly seized and he was sliding along with bikes all round him! I told Mr Hopwood that if we could not do something about the crankshaft breakages we should drop the racing twin. He pointed out that as far as Lashmar was concerned it was his own bike and he could do what he liked with it, but the policy of the factory was to make a twin. I felt we should make a new crank for it to which he agreed and wanted to know if I had any suggestions. By this time Group Research were in the picture at BSA and they demonstrated to me in ten minutes what I had suspected for years. They came up with some very good ideas. One was that the crank needed larger crankpin journals .which would make it stiffer and get away from the frequency at which it now vibrated. Mr Hopwood agreed that their suggestions were fine for 1955 but at that time we had to use what we had. He was interested to know if any other suggestions and Group Research said to put a rolled radius around the ends of each crankpin. They demonstrated by putting a standard crankshaft on vee blocks over the Back to top of the electro-magnetic vibrator they had built.
Then started some sort of motor generator. The noise was like standing next to a jet engine at the airport, it went into a scream and from a scream to an outer pitch sound, onto another phase even higher, then they brought in the electro-magnetic vibrator and the whole place began to buzz. The frequency of the vibrator was adjusted to a multiple of 6,600, the crank vibrated with a high speed buzz, inside ten minutes there was a loud bang, the crank fell in two parts, broken at the usual point, showing the same sort of fracture that we had experienced after three hours running at 6600 RPM. It was a much quicker way of testing a crankshaft and without wrecking an engine. Next they set up one of their special cranks, with the rolled filet radius on the crankpin, it was subjected to the same test, buzzing away on the vee blocks, ten minutes passed, thirty minutes and it was still in one piece. I got tired of waiting and asked to be informed when it broke. It did not break and after one hour it was still good. I was very impressed and so was Mr Hopwood but the factory again did not seem interested, perhaps they could not believe it. This rolling process consisted of applying a ball ended tool to the radius under high pressure in a big lathe.
A few cranks were made, some for research, some for use on the dyno. It seemed fantastic that this simple process could make such a difference. Many years later when I was working for Volkwagen in the USA. I discovered that they cured a rash of broken crankshafts on the 1965 truck engine by the same procedure, except that they did not use a ball, but a small roller to form the radius. It cured the problem for Volkswagen.
Twin engines for Formula 3 We made a number of A7 race engines for this small race class in 1953. They were set up to run on alcohol fuel but were not very reliable and although we got close on 50bhp were repeatedly beaten by Norton singles doing far less. We actually 'borrowed' a 500 Norton engine designed for a formula 3 car, it pulled 42bhp but had 39 ft lbs of torgue against our 36 ft lbs. Part of the trouble with our engines was the installation, they did not get enough cooling air and in one case they had a restricted oil supply, using a long small bore hose from the tank to the engine, the sticky Castor oil simply would not flow fast enough. Another problem was at the head to cylinder block joint, there was a tendency when very hot for a slight blow across to the oil drain holes thus pressurising the crankcase, this blew oil out of the crankcase at every possible point. The cure was to fit small hollow dowels into the head and barrel joint, thus rigidly locating the head, and keeping gas pressure out of the crankcase.
The single overhead camshaft A7 In 1952 they were working on a single overhead camshaft 500 twin. It was a handsome engine with alloy head and barrel, fine pitch finning, exhaust pipe held to the head by nuts. The single overhead cam was driven by bevel gears and a shaft running up what would normally be the push rod tunnel, the valves were operated by rockers. Arthur Bridgewood was working on it in great secrecy in a little shop at the end of the test shop, he had to put up with the noise and fumes of engines being tested. At this point in time it gave the same power as the A7 push rod engine and broke crankshafts with equal regularity. The camshaft was lubricated by the rocker feed which was completely inadequate and of course it wore out cams and nd rockers. Doug Hele suggested using a single wide cam as they did on some Ariels. This cured the rapid wear but the performance suffered due to the geometry of the rockers to cams, one rocker being a trailing rocker, the other a leading one this giving different opening diagram for each valve. I personally felt that the engine could have been made to go if I had been given more freedom as I had with the Gold Star and MC4. One problem was excessive oil consumption due to an accumulation of oil in the rocker box which ran down the valve guides. This we cured by using a C11 oil scavenger pump to pump surplus oil direct to the tank. The feed side of the little oil pump was used to squirt oil through 1/16th holes on to the cam lobes, this cured the rocker and cam wear. At this point we needed a stronger crankshaft and a different design of cams to take advantage off the overhead cam arrangement. By this time Mr Hopwood had lost interest in the engine and said he did not think it would ever be any good, so scrap it. I think that’s what finally happened to it.
The A10 was if anything worse than the A7 when it came to vibration and crankshaft breakages because of its longer stroke. Actually most complaints were about the A10. Although the A7 was the one we raced so that we were more intimately involved in its development. BSA brought about their own demise by their attitude to progress. A favourite saying of Mr Leakes was "Don’t let us be pioneers". Back in the dim and distant past they had lost money on a few experimental ideas that had not worked and that had never been forgotten. Nevertheless when you are the biggest motor cycle manufacturer s in the world you have got to do some pioneering if you want to stay on Back to top. You cannot leave it to small firms like Velocette, who introduced foot gear-change, a successful spring frame, eccentric rocker spindles, a production overhead camshaft engine and many other innovations.
Alloy heads for the twins About the beginning of 1954 it was decided to make a production version of the twin with an alloy head, we had made experimental ones before for the racing people. The head had shrunk in valve seats which gave very little trouble but the spark plugs fitted into bronze inserts screwed and pinned into the head, these persisted in coming out when the plug was removed. I persuaded Mr Hopwood to use long reach plugs screwed directly into the aluminium head, this was very satisfactory. At one stage we could not make a decision on which was best, a single inlet port and one carburettor or twin ports and two carburettors, on the dyno there was very little in it. The first of the Star twins had twin port heads with detachable manifold, it could be used with either one or two carburettors. In point of fact the difference in power is only worth while when running on open pipes. Twin carbs and their cables have to be carefully adjusted to keep both cylinders pulling equally at small throttle openings and just off idling, which is a nuisance to the rider at best, assuming he can cope with the bit of DIY mechanical skill necessary.
After a year we had improved the port configuration and it ran so much better with one big carb that the twin carb option was dropped. We had found it useful to measure the capacity of the inlet ports and check on performance, about 142 to 150cc's gave optimum results. If an engine was down for power we often found the ports undersize. Like all aluminium cylinder heads, these expanded a lot with heads and at the outset we experienced stretched or broken head bolts. These bolts went downwards through the head into the iron cylinder block and would usually break at the root of the last thread, which was the weakest point because it took all the stretching. To overcome this we quite simply put the bolts in a lathe and reducing the diameter of the pIain portion to 10% less than the diameter of the root of the thread. This meant that the thread was no longer the weakest point and that the plain portion could stretch without exceeding its elastic limit.
This was completely successful on the first attempt and no more trouble was experienced with the bolts. They could stretch when the head expanded and return to their original length as the head cooled own. When the new twins were going into production however, Alan Jones who was Works Manager at that time phoned me to say they were unable to make the head bolt as needed, despite my pointing out that we bad found them necessary, he just continued to say they were unable to make them. I went on with my work and forgot about the matter, but I did not have to wait long, within a few hours the motor cycle test shop foreman was on the phone to me complaining the head bolts of the new twins were breaking right and left, so I referred him to Alan Jones. Mr Jones reiterated they were unable to make the bolts we had designed. Prior to this last call I had taken the precaution of calling the drawing office to say that Jones would not follow their drawings of the bolt thus securing an ally. Alan Jones got no sympathy when he had to pull all the bikes concerned back, dismantle the engines and use the bolt we had specified.
I have never liked the air cooled vertical twin, but they looked neat, were simple, had an even firing, smooth exhaust note, fitting neatly into the same frame as their predecessors, the singles. The vibration was terrible, it seemed worse than the single, at least it was more noticeable. To my mind the head joint on all vertical twins with one-piece heads and cylinder block was marginal and subject to distortion. At BSA we must have done a fantastic amount of work on twins, judging by my notes. BSA had made up their minds that the twin was the motor cycle engine of the future. Every time I rode one it gave me the willies - the vibration was so noticeable. We tried all sorts of cures to get rid of the shakes and I still think our best ever effort in that direction was a short stroke 500 we made in 1953. Charlie Salt & I ran and ran it until we wore it out but no one seemed interested in it. This short stroke engine was a 500 A7 using a 650 head, barrel and pistons slightly modified. The crank was machined from the solid. This arrangement gave a 70 x 64.5 bore and stroke and instead of having a bolt on flywheel it had a triangular bob weight machined in the centre of the crank and discs next to the journal bearings. It was a very smooth running engine, both on the dyno and on the road. Power output was similar to the Star Twin, using 7.25:1 compression ratio.
With further tuning and lighter valve gear it gave 36bhp at 7000 a specially developed two into one exhaust system, we got as much as 39 horsepower at 7000. It was a most exciting machine to ride, as you accelerated it went on a normal power curve, then suddenly the exhaust note would change and it would 'yowl' right on up to maximum about 107mph Back in 1953 on low octane petrol this was quite an exciting performance on the road. Charlie and I enjoyed that engine.
The so-called Star Twin camshaft was a sporty one designed I think by Jack Amott although the design office never gave him credit for it. It was quite useable on the road with silencers fitted and also useful with open pipes. The fellows in my shop told me Jack did all the work on cams and I have no reason to doubt their words. Later on we went to the Daytona camshaft which was really a race cam and not very good at low revs but good at high speeds. Amott did design a racing cam for the twin, but we were unable to make it work properly, it was too radical and hard on valve springs. Reg Wilkes mentioned that if the drawing office had stuck to Jack’s original design they would have been all right. I asked to see Amott's original design and Reg got his camshaft out of a cabinet and showed it to me. It had a much larger base circle than the drawing office version, although to be quite honest I could not see what effect this would have. Wilkes suggested I try it sometime, he was sure it would work better and it did. It was still pretty radical. I never could understand why the drawing office decided to change the base circle diameter. One of the disadvantages of a larger base circle is a higher rubbing speed on the other hand you can get a smoother easier ???
Twin camshaft problems. Whilst working at BSA Dennis Lashmar carried on racing my old 'Pike BSA' with the alloy twin engine. I think he had one good win on a wet day at Snetterton, when it ran cool enough not to blow up. Latterly whenever we went to Silverstone or anywhere to watch him, he finished up sliding along on his backside at about 100mph with a broken crankshaft. This was too dangerous I considered. Once just after the massed start at Silverstone, with the pack all bunched up and approaching Woodcote corner at over 100mph the Beesa suddenly seized and he was sliding along with bikes all round him! I told Mr Hopwood that if we could not do something about the crankshaft breakages we should drop the racing twin. He pointed out that as far as Lashmar was concerned it was his own bike and he could do what he liked with it, but the policy of the factory was to make a twin. I felt we should make a new crank for it to which he agreed and wanted to know if I had any suggestions. By this time Group Research were in the picture at BSA and they demonstrated to me in ten minutes what I had suspected for years. They came up with some very good ideas. One was that the crank needed larger crankpin journals .which would make it stiffer and get away from the frequency at which it now vibrated. Mr Hopwood agreed that their suggestions were fine for 1955 but at that time we had to use what we had. He was interested to know if any other suggestions and Group Research said to put a rolled radius around the ends of each crankpin. They demonstrated by putting a standard crankshaft on vee blocks over the Back to top of the electro-magnetic vibrator they had built.
Then started some sort of motor generator. The noise was like standing next to a jet engine at the airport, it went into a scream and from a scream to an outer pitch sound, onto another phase even higher, then they brought in the electro-magnetic vibrator and the whole place began to buzz. The frequency of the vibrator was adjusted to a multiple of 6,600, the crank vibrated with a high speed buzz, inside ten minutes there was a loud bang, the crank fell in two parts, broken at the usual point, showing the same sort of fracture that we had experienced after three hours running at 6600 RPM. It was a much quicker way of testing a crankshaft and without wrecking an engine. Next they set up one of their special cranks, with the rolled filet radius on the crankpin, it was subjected to the same test, buzzing away on the vee blocks, ten minutes passed, thirty minutes and it was still in one piece. I got tired of waiting and asked to be informed when it broke. It did not break and after one hour it was still good. I was very impressed and so was Mr Hopwood but the factory again did not seem interested, perhaps they could not believe it. This rolling process consisted of applying a ball ended tool to the radius under high pressure in a big lathe.
A few cranks were made, some for research, some for use on the dyno. It seemed fantastic that this simple process could make such a difference. Many years later when I was working for Volkwagen in the USA. I discovered that they cured a rash of broken crankshafts on the 1965 truck engine by the same procedure, except that they did not use a ball, but a small roller to form the radius. It cured the problem for Volkswagen.
Twin engines for Formula 3 We made a number of A7 race engines for this small race class in 1953. They were set up to run on alcohol fuel but were not very reliable and although we got close on 50bhp were repeatedly beaten by Norton singles doing far less. We actually 'borrowed' a 500 Norton engine designed for a formula 3 car, it pulled 42bhp but had 39 ft lbs of torgue against our 36 ft lbs. Part of the trouble with our engines was the installation, they did not get enough cooling air and in one case they had a restricted oil supply, using a long small bore hose from the tank to the engine, the sticky Castor oil simply would not flow fast enough. Another problem was at the head to cylinder block joint, there was a tendency when very hot for a slight blow across to the oil drain holes thus pressurising the crankcase, this blew oil out of the crankcase at every possible point. The cure was to fit small hollow dowels into the head and barrel joint, thus rigidly locating the head, and keeping gas pressure out of the crankcase.
The single overhead camshaft A7 In 1952 they were working on a single overhead camshaft 500 twin. It was a handsome engine with alloy head and barrel, fine pitch finning, exhaust pipe held to the head by nuts. The single overhead cam was driven by bevel gears and a shaft running up what would normally be the push rod tunnel, the valves were operated by rockers. Arthur Bridgewood was working on it in great secrecy in a little shop at the end of the test shop, he had to put up with the noise and fumes of engines being tested. At this point in time it gave the same power as the A7 push rod engine and broke crankshafts with equal regularity. The camshaft was lubricated by the rocker feed which was completely inadequate and of course it wore out cams and nd rockers. Doug Hele suggested using a single wide cam as they did on some Ariels. This cured the rapid wear but the performance suffered due to the geometry of the rockers to cams, one rocker being a trailing rocker, the other a leading one this giving different opening diagram for each valve. I personally felt that the engine could have been made to go if I had been given more freedom as I had with the Gold Star and MC4. One problem was excessive oil consumption due to an accumulation of oil in the rocker box which ran down the valve guides. This we cured by using a C11 oil scavenger pump to pump surplus oil direct to the tank. The feed side of the little oil pump was used to squirt oil through 1/16th holes on to the cam lobes, this cured the rocker and cam wear. At this point we needed a stronger crankshaft and a different design of cams to take advantage off the overhead cam arrangement. By this time Mr Hopwood had lost interest in the engine and said he did not think it would ever be any good, so scrap it. I think that’s what finally happened to it.
The A10 was if anything worse than the A7 when it came to vibration and crankshaft breakages because of its longer stroke. Actually most complaints were about the A10. Although the A7 was the one we raced so that we were more intimately involved in its development. BSA brought about their own demise by their attitude to progress. A favourite saying of Mr Leakes was "Don’t let us be pioneers". Back in the dim and distant past they had lost money on a few experimental ideas that had not worked and that had never been forgotten. Nevertheless when you are the biggest motor cycle manufacturer s in the world you have got to do some pioneering if you want to stay on Back to top. You cannot leave it to small firms like Velocette, who introduced foot gear-change, a successful spring frame, eccentric rocker spindles, a production overhead camshaft engine and many other innovations.
Alloy heads for the twins About the beginning of 1954 it was decided to make a production version of the twin with an alloy head, we had made experimental ones before for the racing people. The head had shrunk in valve seats which gave very little trouble but the spark plugs fitted into bronze inserts screwed and pinned into the head, these persisted in coming out when the plug was removed. I persuaded Mr Hopwood to use long reach plugs screwed directly into the aluminium head, this was very satisfactory. At one stage we could not make a decision on which was best, a single inlet port and one carburettor or twin ports and two carburettors, on the dyno there was very little in it. The first of the Star twins had twin port heads with detachable manifold, it could be used with either one or two carburettors. In point of fact the difference in power is only worth while when running on open pipes. Twin carbs and their cables have to be carefully adjusted to keep both cylinders pulling equally at small throttle openings and just off idling, which is a nuisance to the rider at best, assuming he can cope with the bit of DIY mechanical skill necessary.
After a year we had improved the port configuration and it ran so much better with one big carb that the twin carb option was dropped. We had found it useful to measure the capacity of the inlet ports and check on performance, about 142 to 150cc's gave optimum results. If an engine was down for power we often found the ports undersize. Like all aluminium cylinder heads, these expanded a lot with heads and at the outset we experienced stretched or broken head bolts. These bolts went downwards through the head into the iron cylinder block and would usually break at the root of the last thread, which was the weakest point because it took all the stretching. To overcome this we quite simply put the bolts in a lathe and reducing the diameter of the pIain portion to 10% less than the diameter of the root of the thread. This meant that the thread was no longer the weakest point and that the plain portion could stretch without exceeding its elastic limit.
This was completely successful on the first attempt and no more trouble was experienced with the bolts. They could stretch when the head expanded and return to their original length as the head cooled own. When the new twins were going into production however, Alan Jones who was Works Manager at that time phoned me to say they were unable to make the head bolt as needed, despite my pointing out that we bad found them necessary, he just continued to say they were unable to make them. I went on with my work and forgot about the matter, but I did not have to wait long, within a few hours the motor cycle test shop foreman was on the phone to me complaining the head bolts of the new twins were breaking right and left, so I referred him to Alan Jones. Mr Jones reiterated they were unable to make the bolts we had designed. Prior to this last call I had taken the precaution of calling the drawing office to say that Jones would not follow their drawings of the bolt thus securing an ally. Alan Jones got no sympathy when he had to pull all the bikes concerned back, dismantle the engines and use the bolt we had specified.
Roland Pike Autobiography - Chapter 20
Tales of the Bantam C12, C15 & MC4
The BSA Bantam and the Harley Davidson Hummer were snatched from the Germans as 'reparations' after World War II. The Bantam started as a DKW in 1935 or 36 when it was considered modern with its flat Back to top piston, but by 1946 when BSA got it, it was already old fashioned. One could get about 4.5bhp from the 125cc if you were lucky, more often only about 3.5. The noise they made was dreadful and so was the oil they blew all over the test shop. We worked on them for a couple of years, making all sorts of experimental bits and pieces, none of which worked very well. I recall someone wanted to ride one in the International Six Days Trial and Bert Perrigo the BSA Competition manager persuaded us to build him a 'special'.
Reg Wilkes worked on it for a couple of weeks and got 5 or 6bhp over a wider range than the standard machine. Another time an Australian sent us under great secrecy his Bantam which was reputed to be very powerful and high revving and all the rest. It was highly modified and ran on alcohol blended fuel, they claimed 12bhp and had been timed to exceed 90mph We were suitably impressed and set it up on our dyno, we mixed the prescribed blend of fuel of alcohol benzole and acetone and ran it. However we could not stop it from four stroking and it would not give more than 6bhp. We were reluctant to jet it down in case we burned it up. So we gave up, deciding that the cold damp November air did not suit it, it apparently needed hot dry Aussie air.
In the development shop at BSA we used to hate the sound and sight of the Bantam. When I first went there we were responsible for Bantam development, but I disliked two strokes then and I still do. I suggested to Hopwood why didn’t he get Herman Meier who had been with on the Continental Circus trip in 1951 who was an enthusiast as I felt sure he would make them run. Finally after a lot of trouble with work permits and so on we got Herman over and he shared an office with me. He doubled the power of the Bantam in a few months. Unfortunately Herman was a temperamental type and I eventually recommended that he be moved to Redditch where the Bantams were made anyway. Here he got some good power outputs from the 125cc Bantam and developed the larger versions they eventually produced.
Occasionally a 250 C12 came into the shop, this was a simple and cheap engine, designed in 1935 as a light and inexpensive utility machine based on a Blackburn design used by Excelsior and Frances Barnett a year or earlier. It was novel in that the push rods crossed in the tunnel at the same angle as the valves.
One day the C12 production line was stopped due to repeated complaints from the Dealers of 'knock' from the engine. Mr Leake called a meeting of everyone concerned and told us to cure it or it would have to be dropped from production. A big panic ensued, several engines that were 'knockers' were brought into my shop and we found the in some cases the knock could be cured by retarding the ignition very slightly, but some of the worst examples 'knocked' regardless of timing etc. These were stripped right down for thorough examination, we noticed that the flywheels were made of cast iron whereas when the engine was first produced it had flywheels of steel stampings. We were able to get some of these and when fitted to the worst offenders it completely cured the problem. Whilst fiddling with C12 250cc we tried the alloy cylinder head from the Ariel Colt, a 200cc version of the same engine, this cylinder head cured 'knocking' and gave more power, which prompted us to make a 'deluxe' C12 which after a few quite simple modifications gave 15bhp. An engine was passed to the experimental dept for road testing, but I do not remember any conclusions being made and soon after the 015 was designed. This was another 'cheap' design based on the Triumph Terrier 150cc. In my opinion a poor thing.
The MC4 design which was very promising was essentially half an A7 twin, the better half I thought as it was more reliable than the A7. It was intended to make a 350cc version using A10 parts. This would have been helpful to the production people as so many parts would have been interchangeable. The camshaft had to be different of course for a single cylinder. The original design used a one-piece iron casting unfortunately the cast iron was not up to the job and the first one broke, possibly 'Nodular' iron would have done the trick or the larger crankpin as used later in A7 & A10 would have helped. At about this time (1952) we used our first alternators built into the engine timing case, this gave it an odd shaped bulge, they worked very well and used less horsepower than the regular generator with rotating armature. I think if it had gone into production some resistance would have been encountered from the typical motor cyclist over the odd appearance of this engine, but once they realised the advantages of the engine they would soon forget the appearance.
The MC4 gave half the power of the racing A7 but with much greater reliability. This could only be explained by the fact that the main bearings were only some three inches apart giving an inherently more rigid lower end than the A7, which suffered from crankshaft whip. One of the things we learned a lot about during the MC4 development was mechanical berathers. As designed it had a disc valve breather as on the earlier Gold Star, at high revolutions the little pen steel disc valve could not cope and as a result blew oil out in large amounts. The same problem on the early Gold Star caused several retirements in the Clubmans TT races due to loss of oil and too much oil on the rear tire became very mechanical breather conscious and tried to adapt the A7 mechanical breather to the MC4. At first it would not work satisfactorily finally we fitted copper pipe inside the crankcase, picking up breather air from a 'dry' spot in the corner of the crankcase. This was much more effective in terms of oil loss, but the crankcase pressure was disappointing until we retarded the timing of the breather valve by 70 degrees, it would then maintain a pressure inside the crankcase of between of 4 and 7 inches of water lower than atmospheric at all speeds. This kept the engine very clean, even when belting round MonthIery track at nearly 100mph.
Due to the MIRA test track not being completed we arranged to go to France and use the banked track at Monthlery for a week. We.loaded the MC4, a 350 Gold Star and two 650 A10 Police Specials into our van, which was my old race van which I had bought from Ray Amm in 1952, now fitted' with a V8 engine. Charlie Salt and I were the hobbledeboys, we drove the van via Dover and Boulogne to Paris. Arthur Lupton and Bert Hopwood drove an A40 Austin. Bill Nichols flew out to join us a little later. Strangely enough although Bill was such a dare-devil in Scrambles and on the road, he was completely over-awed by the banked track. He was unable to lap as fast as I did and I was putting on weight and my leathers were tight. Charlie being neat and slim lapped about 3mph faster than I did and I was a little faster than Bill. The demonstration of the police bikes to the National Guard was the funniest thing. The police were all Triumph enthusiasts and did not like BSAs. When our bikes lapped faster than the Police Triumphs they removed the silencers, saying "now we will go faster". We wondered whether we should remove our silencers as well and go faster still, but it was getting ridiculous. Their police model Triumph had the infamous sprung hub and at speed on the banking looked positively dangerous. It started to drizzle with rain and I thought now we will show them, our bikes had the old plunger springing, it seemed steadier than the Triumph on the banking. However they would not ride on the track in the wet. I did a couple of fast laps in the wet at about 103mph and was skating about all over the place. So we adjourned for lunch with the Distributor and his guests from the Guard Nationale. We spent the rest of our time there testing the MC4 and found the heavy front mudguards were holding our speed down to 93mph, so we removed front mudguard and tipped the headlamp to try and improve the streamlining - we could not remove jt because it contained switchgear etc. The bike was road equipped except for a megaphone in place of the silencer. This put the speed up to 96 for the lap. When timed the Gold Star and Charlie slipstreamed me on the MC4 we lapped at just on 99mph. When we switched bikes we could lap at 97. For a 250cc push rod machine which was not designed as a racer these times were very good, the engine was putting out about 24.5bhp. The racing Excelsior 250 claimed 22.5bhp on 50/50 petrol benzole. We were using pump fuel of 78 octane. However when we returned to the factory the Board of Directors decided against producing the MC4 which was a great disappointment to all of us, we who had seen its promise. A version was assembled with sheet metal covering over crankcase and gearbox, a different colour scheme and Sunbeam name on the tank, this was also turned, down. The C12 and its variations stayed in production.
The BSA Bantam and the Harley Davidson Hummer were snatched from the Germans as 'reparations' after World War II. The Bantam started as a DKW in 1935 or 36 when it was considered modern with its flat Back to top piston, but by 1946 when BSA got it, it was already old fashioned. One could get about 4.5bhp from the 125cc if you were lucky, more often only about 3.5. The noise they made was dreadful and so was the oil they blew all over the test shop. We worked on them for a couple of years, making all sorts of experimental bits and pieces, none of which worked very well. I recall someone wanted to ride one in the International Six Days Trial and Bert Perrigo the BSA Competition manager persuaded us to build him a 'special'.
Reg Wilkes worked on it for a couple of weeks and got 5 or 6bhp over a wider range than the standard machine. Another time an Australian sent us under great secrecy his Bantam which was reputed to be very powerful and high revving and all the rest. It was highly modified and ran on alcohol blended fuel, they claimed 12bhp and had been timed to exceed 90mph We were suitably impressed and set it up on our dyno, we mixed the prescribed blend of fuel of alcohol benzole and acetone and ran it. However we could not stop it from four stroking and it would not give more than 6bhp. We were reluctant to jet it down in case we burned it up. So we gave up, deciding that the cold damp November air did not suit it, it apparently needed hot dry Aussie air.
In the development shop at BSA we used to hate the sound and sight of the Bantam. When I first went there we were responsible for Bantam development, but I disliked two strokes then and I still do. I suggested to Hopwood why didn’t he get Herman Meier who had been with on the Continental Circus trip in 1951 who was an enthusiast as I felt sure he would make them run. Finally after a lot of trouble with work permits and so on we got Herman over and he shared an office with me. He doubled the power of the Bantam in a few months. Unfortunately Herman was a temperamental type and I eventually recommended that he be moved to Redditch where the Bantams were made anyway. Here he got some good power outputs from the 125cc Bantam and developed the larger versions they eventually produced.
Occasionally a 250 C12 came into the shop, this was a simple and cheap engine, designed in 1935 as a light and inexpensive utility machine based on a Blackburn design used by Excelsior and Frances Barnett a year or earlier. It was novel in that the push rods crossed in the tunnel at the same angle as the valves.
One day the C12 production line was stopped due to repeated complaints from the Dealers of 'knock' from the engine. Mr Leake called a meeting of everyone concerned and told us to cure it or it would have to be dropped from production. A big panic ensued, several engines that were 'knockers' were brought into my shop and we found the in some cases the knock could be cured by retarding the ignition very slightly, but some of the worst examples 'knocked' regardless of timing etc. These were stripped right down for thorough examination, we noticed that the flywheels were made of cast iron whereas when the engine was first produced it had flywheels of steel stampings. We were able to get some of these and when fitted to the worst offenders it completely cured the problem. Whilst fiddling with C12 250cc we tried the alloy cylinder head from the Ariel Colt, a 200cc version of the same engine, this cylinder head cured 'knocking' and gave more power, which prompted us to make a 'deluxe' C12 which after a few quite simple modifications gave 15bhp. An engine was passed to the experimental dept for road testing, but I do not remember any conclusions being made and soon after the 015 was designed. This was another 'cheap' design based on the Triumph Terrier 150cc. In my opinion a poor thing.
The MC4 design which was very promising was essentially half an A7 twin, the better half I thought as it was more reliable than the A7. It was intended to make a 350cc version using A10 parts. This would have been helpful to the production people as so many parts would have been interchangeable. The camshaft had to be different of course for a single cylinder. The original design used a one-piece iron casting unfortunately the cast iron was not up to the job and the first one broke, possibly 'Nodular' iron would have done the trick or the larger crankpin as used later in A7 & A10 would have helped. At about this time (1952) we used our first alternators built into the engine timing case, this gave it an odd shaped bulge, they worked very well and used less horsepower than the regular generator with rotating armature. I think if it had gone into production some resistance would have been encountered from the typical motor cyclist over the odd appearance of this engine, but once they realised the advantages of the engine they would soon forget the appearance.
The MC4 gave half the power of the racing A7 but with much greater reliability. This could only be explained by the fact that the main bearings were only some three inches apart giving an inherently more rigid lower end than the A7, which suffered from crankshaft whip. One of the things we learned a lot about during the MC4 development was mechanical berathers. As designed it had a disc valve breather as on the earlier Gold Star, at high revolutions the little pen steel disc valve could not cope and as a result blew oil out in large amounts. The same problem on the early Gold Star caused several retirements in the Clubmans TT races due to loss of oil and too much oil on the rear tire became very mechanical breather conscious and tried to adapt the A7 mechanical breather to the MC4. At first it would not work satisfactorily finally we fitted copper pipe inside the crankcase, picking up breather air from a 'dry' spot in the corner of the crankcase. This was much more effective in terms of oil loss, but the crankcase pressure was disappointing until we retarded the timing of the breather valve by 70 degrees, it would then maintain a pressure inside the crankcase of between of 4 and 7 inches of water lower than atmospheric at all speeds. This kept the engine very clean, even when belting round MonthIery track at nearly 100mph.
Due to the MIRA test track not being completed we arranged to go to France and use the banked track at Monthlery for a week. We.loaded the MC4, a 350 Gold Star and two 650 A10 Police Specials into our van, which was my old race van which I had bought from Ray Amm in 1952, now fitted' with a V8 engine. Charlie Salt and I were the hobbledeboys, we drove the van via Dover and Boulogne to Paris. Arthur Lupton and Bert Hopwood drove an A40 Austin. Bill Nichols flew out to join us a little later. Strangely enough although Bill was such a dare-devil in Scrambles and on the road, he was completely over-awed by the banked track. He was unable to lap as fast as I did and I was putting on weight and my leathers were tight. Charlie being neat and slim lapped about 3mph faster than I did and I was a little faster than Bill. The demonstration of the police bikes to the National Guard was the funniest thing. The police were all Triumph enthusiasts and did not like BSAs. When our bikes lapped faster than the Police Triumphs they removed the silencers, saying "now we will go faster". We wondered whether we should remove our silencers as well and go faster still, but it was getting ridiculous. Their police model Triumph had the infamous sprung hub and at speed on the banking looked positively dangerous. It started to drizzle with rain and I thought now we will show them, our bikes had the old plunger springing, it seemed steadier than the Triumph on the banking. However they would not ride on the track in the wet. I did a couple of fast laps in the wet at about 103mph and was skating about all over the place. So we adjourned for lunch with the Distributor and his guests from the Guard Nationale. We spent the rest of our time there testing the MC4 and found the heavy front mudguards were holding our speed down to 93mph, so we removed front mudguard and tipped the headlamp to try and improve the streamlining - we could not remove jt because it contained switchgear etc. The bike was road equipped except for a megaphone in place of the silencer. This put the speed up to 96 for the lap. When timed the Gold Star and Charlie slipstreamed me on the MC4 we lapped at just on 99mph. When we switched bikes we could lap at 97. For a 250cc push rod machine which was not designed as a racer these times were very good, the engine was putting out about 24.5bhp. The racing Excelsior 250 claimed 22.5bhp on 50/50 petrol benzole. We were using pump fuel of 78 octane. However when we returned to the factory the Board of Directors decided against producing the MC4 which was a great disappointment to all of us, we who had seen its promise. A version was assembled with sheet metal covering over crankcase and gearbox, a different colour scheme and Sunbeam name on the tank, this was also turned, down. The C12 and its variations stayed in production.
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