The problems & politics of BSA in the 1950's
Here is a little poem I made up.
The Motor Cycle Industry.
The labourers toiled, the craftsmen wrought,
The Draftsmen drew, the thinkers thought,
The planners planned, the salesmen sold,
But the bikes they sold looked very old.
Thats not to say they were not fine,
But ancient was the whole design.
The buyers paid their hard-earned gold -
For new machines that looked like old.
Designers sat and wracked their brains,
And got rude answers for their pains.
The things they drew were not too bold,
With ideas that were centuries old,
The stylist and the artist came
And still the drawings looked the same.
The conception lacked that final touch
Of which the keen demand so much.
Just then there came that way by chance
A lad who knew he could enhance
The models' looks and make them go
If only they would let him show.
He was taken at his word, and then
Got out his papers, books and pen.
Set down his ideas, plans and thought
He'd told them all, and kept back nought.
"Oh that won't work, nor that" they cried
As new ideas were made and tried.
Or when they did, the critics say
"We thought of that before today"
"That one's no good" they said in test,
"The ancient ones were always best".
They were so clever with their tricks, They ousted him with politics.
Triumphs came into BSA at the end of 1956 and took charge of the company that had bought it, only a few years before. Jack Sangster sold Triumph to BSA for $4 million, but somehow he still controlled Triumph and eventually got control of both companies.
This move did not seem to do BSA any good, they already appeared to be on a slippery road and no one appeared to know what to do to stop the slide. They laid off or fired 400 production workers at the end of 1956 and another 400 people at the beginning Of 195. This last 400 included skilled personnel, they were selected purely by seniority which was a big mistake as it left them with a lot of chiefs and no indians.
Some of those retained had not done anything useful for years but were just hanging on for their pensions. Triumph although they had high production figures did not produce as much of their motor cycles as BSA who owned Idoson Motor Cylinders, Monochrome, Jessups Steel and several small suppliers.
When BSA bought Triumphs it would have been logical for a BSA man to have been put in charge at Triumphs and to have them use BSA forgings, Daimler & Idoson castings and their research group to work in Group research at Small Heath, but that is not the way it turned out.
The class structure at BSA was quite feudal, there was no sense of democracy. You could not go upstairs to the Managers office without the Commissionaire escorting you unless you were part of management. There were five different eating areas. One for the Directors, a Monthly staff room, Foreman’s dining room, office dining room and the workers canteen. I suppose there was something to be said for this, but in this day and age most companies would have reduced the number of dining rooms to two or three.
Showing posts with label Roland Pike. Show all posts
Showing posts with label Roland Pike. Show all posts
Sunday, 8 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 21
Of 250cc Gold Stars
During 1953 a Mr Thorpe persuaded Bert Perrigo that he should allow us to build a 250 Gold Star on a one off basis and a promise not to worry us for special tuning or special parts. I was quite keen to do this having always been interested in the 250 class. We had one of the experimental small valve scrambler heads left over and an experimental short 6" steel connecting rod, also a special pair of flywheels with crankpin holes specially machined to give 63 mm stroke. The crankpin was special for these short stroke flywheels in that the roller bearing in the centre was standard but the portion that fitted in the flywheels was smaller than usual, being 1.00" diameter and 0.00l taper giving a press fit, the nuts just keeping things together. With this very short stroke there was not room for the standard crankpin nuts. We made special long round nuts with a protruding hexagonal head these were cut off close to the pin after tightening. To remove them they were split with a chisel.
A standard 71mm bore piston and cylinder was used, suitably shortened. Alloy tubular pushrods were used, with lightened tappets, eccentric rocker spindles were used. After experimenting with several cams 22bhp was attained at 7000 – 7600RPM. The engine did not give as much power as the MC4 and it is quite likely that with further running the power increased but it proved very reliable and Mr Thorpe ran it for some years. Later on we built another Gold Star 250, this time using a one-piece crankshaft with outside flywheel and a Sunbeam S7 connecting rod with plain big end. This engine had a 1953 350 Gold Star head and cylinder barrel, the cylinder had to be shortened considerably only seven fins remaining. After quite a small amount of running 26.2bhp was obtained, then the inlet valve broke which ruined the head. When the engine was rebuilt a late type big fin cylinder head was used, a different cylinder head holding down arrangement was used, short steel tubes screwed into the crankcase, bolts fitted from the Back to top screwing into tubes, only four were used and we had no head blowing.
This was the final arrangement of our 250 Gold Star, it proved very successful, the best power recorded being 29.6 at 8250. It would run up to 9000 RPM quite reliably. The inlet port was a pressed in piece of alloy machined after fitting which gave a very straight port. Several engines were built to this design, one was a 350cc, using an 85 mm 500 Gold Star piston on a 61.5 stroke, this was later converted to a 250 by fitting a 72 mm Gold Star piston and was used in the Geoff Monty Special (GMS) for several years. Obviously these 250's were what could best be called ‘codge-ups' using 500 style crankcases for lack of a proper one, the cylinder heads being from 350s had unsuitable valve angles and sizes, the compression ratios were restricted, because of wide angle valves. In spite of these disadvantages proved in the GMS that this was the way to go. The lessons learnt from the ill-fated MC1 were not forgotten. The 250 Gold Star engine in a 500 Gold Star frame was timed at MIRA to do 108mph. In the GMS with some fairing it reached 115mph.
During 1953 a Mr Thorpe persuaded Bert Perrigo that he should allow us to build a 250 Gold Star on a one off basis and a promise not to worry us for special tuning or special parts. I was quite keen to do this having always been interested in the 250 class. We had one of the experimental small valve scrambler heads left over and an experimental short 6" steel connecting rod, also a special pair of flywheels with crankpin holes specially machined to give 63 mm stroke. The crankpin was special for these short stroke flywheels in that the roller bearing in the centre was standard but the portion that fitted in the flywheels was smaller than usual, being 1.00" diameter and 0.00l taper giving a press fit, the nuts just keeping things together. With this very short stroke there was not room for the standard crankpin nuts. We made special long round nuts with a protruding hexagonal head these were cut off close to the pin after tightening. To remove them they were split with a chisel.
A standard 71mm bore piston and cylinder was used, suitably shortened. Alloy tubular pushrods were used, with lightened tappets, eccentric rocker spindles were used. After experimenting with several cams 22bhp was attained at 7000 – 7600RPM. The engine did not give as much power as the MC4 and it is quite likely that with further running the power increased but it proved very reliable and Mr Thorpe ran it for some years. Later on we built another Gold Star 250, this time using a one-piece crankshaft with outside flywheel and a Sunbeam S7 connecting rod with plain big end. This engine had a 1953 350 Gold Star head and cylinder barrel, the cylinder had to be shortened considerably only seven fins remaining. After quite a small amount of running 26.2bhp was obtained, then the inlet valve broke which ruined the head. When the engine was rebuilt a late type big fin cylinder head was used, a different cylinder head holding down arrangement was used, short steel tubes screwed into the crankcase, bolts fitted from the Back to top screwing into tubes, only four were used and we had no head blowing.
This was the final arrangement of our 250 Gold Star, it proved very successful, the best power recorded being 29.6 at 8250. It would run up to 9000 RPM quite reliably. The inlet port was a pressed in piece of alloy machined after fitting which gave a very straight port. Several engines were built to this design, one was a 350cc, using an 85 mm 500 Gold Star piston on a 61.5 stroke, this was later converted to a 250 by fitting a 72 mm Gold Star piston and was used in the Geoff Monty Special (GMS) for several years. Obviously these 250's were what could best be called ‘codge-ups' using 500 style crankcases for lack of a proper one, the cylinder heads being from 350s had unsuitable valve angles and sizes, the compression ratios were restricted, because of wide angle valves. In spite of these disadvantages proved in the GMS that this was the way to go. The lessons learnt from the ill-fated MC1 were not forgotten. The 250 Gold Star engine in a 500 Gold Star frame was timed at MIRA to do 108mph. In the GMS with some fairing it reached 115mph.
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