The Twin-Cam Aston-Martins
As some readers may remember, I wrote a few notes on the Bamford and Martin side-valve Aston-Martin cars some few years ago, and, whilst my first s.v. car is still in the family it is not in my possession, my brother having taken it over after he was demobbed. The four-seater was sold to Mr. Yeates of Eccles, and all I have left is the ex-Zborowski Grand Prix 16-valve car. It is with this car that I now propose to deal and although some mention was made of these cars in my last notes, I feel sure that readers will forgive me if I go over a few points already dealt with.
I suppose one should start at the beginning, so, we find ourselves back in 1921 in the Kensington works of Bamford & Martin, Ltd. On the test bed is a 4-cylinder single o.h.c. 10-valve engine. The side-valve-engined car has just gone into production and a sanction for 100 cars has started the programme. Racing forms the main means of advertising and the sponsor, Lionel Martin, is a one-hundred-per-cent. enthusiast for the sport. He has realised, I suppose, that excellent as the performance of the side-valve cars is, something, just that little bit more potent, is required. He has been, and is to be, extremely successful with his own side-valve car, but his engine is just about tuned to maximum. That original s.v. must have had a very different engine from the more sedate production cars. I do know that it had much drilled con.-rods, no flywheel, just a flat plate with the starter teeth on it, sufficient to carry the clutch, and in all probability a "hotter" camshaft. So along came the single o.h.c. engine. This had been designed by one, Robb, and was, in fact, quite a nice job. Only once have I seen any reference to this engine in detail and that is in a very early copy of the during 1921. The 16 valves were placed vertically in the head, and the camshaft was driven by a vertical shaft drive at the front end, the valves being operated through rocking tappets. Large plates on either side of the cam cover, when detached, gave access to these tappets. The bore and stroke were 65 mm. by 112 mm. and the rating was 10.5 h.p. The crankcase and sump were in many ways similar to the s.v. but much stiffer, also the magneto was driven by a vertical shaft below which was the water pump and oil pump. The oil filters were in the same position as on the s.v., but the oil filler, an enormous affair, was on the exhaust side of the engine.
Well, for some reason or other this engine never seemed to show any advantages over the s.v. and I doubt if it was ever raced. There are certainly no records of its performance in any event. So, the powers who were involved began to cogitate, and this is where Henri comes into the picture. History tells us that one of the old A.M. boys (forgive my term, you Bentley people), R. C. Gallop, had been apprenticed to Peugeot and had come in contact with Henri. He was therefore given the task of persuading the great man to fix up B. & M.s with a design for an o.h.v. engine. This he did and somewhere about Christmas time of 1921 he returned triumphant.
It is generally supposed that Henri had designed the whole of the now famous 16-valve twin-cam engine, but this is not so, for in point of fact, all that he did was to design a head and this is an exact replica of one half of his three-litre Ballot engine and the valves were identical with the then current Peugeot motor-cycle. The cost of the design was a modest £50. Work was commenced immediately on the new design and the lower half of the single-cam engine (not the s.v., as some suppose) was the basis of this new racing engine. A special chassis was made up and here we have in Lionel Martin's own words "Their first real racer." What a perfectly lovely little car it was, too, every part a perfect tool-room job and yet, as is so often the case, there was one little snag. This was in the form of the magneto drive; the magneto was fitted in a vertical position and failure of this instrument (and occasionally valve springs) was the cause of the majority of their setbacks.
As far back as 1930 I had tried one of these cars, which was then owned by a Birmingham enthusiast. It had come into his hands from the late Count Zborowski when, after the Count's death, his cars had been sold. The car then had its original Grand Prix body fitted and a pair of typically-Zborowski front wings. I had at this time tried to persuade my father to buy this car for me as it was once again in the market, but he refused, saying it was far too fierce for a youngster, and so it passed into the hands of a Bristol "enthusiast." This gentleman then decided to rebuild it in no uncertain manner, and the work must have cost a mint of money. After stripping the whole thing down and throwing away the body, the following conversions were made:
1. Lubrication system converted to dry-sump.
2. Right-hand gear change converted to central.
3. Complete revision of braking layout.
4. A brand new 2-seater body.
So that was that, and for the life of me I cannot find any reason at all why some people must take a perfectly sound design and mess it up. One thing only can be said in favour of the modifications and that is that they were done in a most professional and workmanlike way, not in the least amateurish. That was the end of the Zborowski Grand Prix car and so it remained until 1940, when I bought it from the late Robert Hichens. It was not until 1945 that I brought the car out of storage in Cornwall, and since then, I have, to the best of my ability, been restoring it to something of its original glory. Before dealing with the restoration I feel that one point should be cleared up.
It has often been quoted in the Press that the car which I now own was driven by Zborowski in the French Grand Prix of 1922. This I'm inclined to doubt, for various reasons. Two cars were built for the French Grand Prix and one was driven by Zborowski and one by Gallop. Zborowski's car was number 15 and gallop's number was 8. After the race the two cars went back to the works and then, as those who have read G. E. T. Eyston's "Flat Out" will know, Eyston bought No. 15 and also a track car without engine, using, as he tells us, the racing engine in both cars. What happened to the car after Eyston disposed of it is not known to me, but I do know that he also used the engine in his racing motorboat, What a hectic life that poor engine had! Eyston was very successful, however, and won quite a number of events with it. As to the second car, No. 8, this stayed with the works and was driven by Moir, Zborowski & Co. in a number of events before Zborowski finally bought it, and this I believe is my car. Of its life I will speak later; for the present I will deal with the car basically. The details which I give here are all gathered from a close examination of the stripped engine and chassis.
Commencing with the top of the engine, the "Henri half," we have a cast-iron block, cast in one with head. The bore and stroke are 65 mm. by 112 mm. The sides of the block are open cast, and very large jacket plates are used. It has been stated by Mr. Pomeroy in his "Milestones of Speed" series in the Motor that the exhaust valve cooling on this engine is poor, a decision no doubt arrived at after examining a cross-section drawing. On examining the water coring of this block when stripped it seems to be quite adequate, but evidence of heat is very pronounced when one examines the condition of the exhaust valves and their fittings closely. There is, however, no evidence of extreme heating and all the exhaust valves are in excellent condition. In passing I may say that the engine maintains a normal running temperature of about 80° C. The four-valves-per-cylinder are placed at a rather acute angle to the bore, I think about 80°, giving the engine a much taller appearance than with the normal 45° setting. This was probably done in order to fit everything in behind the very slim radiator which these cars had. On the inlet side the valves are 1.312 in. diam. at the head, which is deeply tulip-shaped, tapering gradually to a stem of .8145 in. diam., and on the exhaust side they are 1.187 in. diam. at the head, still tulip-shaped, and the stem is as that of the inlet valve. The valves are hardened. It was not possible to remove some of them without first taking out the valve guides, but these are of the floating type and draw away very easily. At the top of each bore the head flows away into a kind of pocket, no doubt due to the large size of the inlet valves. A sparking plug is placed centrally over the top of each piston. There are two springs to each valve and these are held in position by split cotters. Over this assembly is the usual Henri piston in direct contact with the cams.
The pistons fit over the valve stems and are carried in an aluminium-alloy casing, which forms the lower half of the cam box and is machined to carry small ball-bearings in which the camshafts run. Each shaft has 8 cams cut on it, the inlet being a high-lift, sharply-tipped cam, and the exhaust a high-lift with a slight dwell period on the tip. The aluminium camshaft covers, alone, hold these shafts in position. The unit at the front of the block which houses the camshaft drive is interesting and is in the form of a rather complicated alloy casting shaped to carry a pair of bevels and three straight-toothed spur wheels. The drive to the camshafts, being by a vertical shaft at the front of the engine, calls for a pair of bevels at the top centre, and behind the crown-wheel is a single spur wheel smaller in diameter, which in turn meshes with the wheels on each camshaft. This gear train is carried in its own set of ball hearings and necessary thrust races. The housing is split and a cover casting fits neatly over the top, sealing up the camshaft covers to this front housing.
The porting of this block is quite interesting and is identical, once again, with the 3-litre Ballot. There is one exhaust port split into two for each cylinder, but on the inlet side there are only two very large rectangular ports covering two cylinders each. These are not split up in any way and each of these chambers opens directly into the cylinders from each carburetter. The water outlet is in the form of a two-branch copper pipe, each branch fitting between the alternate plug sockets. On the water-intake side of the block (the exhaust side) the inlet is cast in with the water jacket cover plate and from there a copper pipe takes a sharp turn through 180° and back between cylinders 2 and 3 and so forward to the pump.
So much for the cylinder block. The crankcase is a very sturdy alloy casting with four bearer arms the machined faces of which form feet which bolt directly to the chassis frame, making the front end very rigid. A pair of bevels take the drive from the front of the crankshaft, via a vertical shaft, to the aforementioned camshaft drive, and from the base of the vertical shaft is driven a train of gears running horizontally across the engine. This is the drive to the magneto, water pump and oil pumps. On top of this gear housing is a steel platform with vertical back, on to which is strapped a normal magneto, the points being on the top. A compressed rubber coupling is used for the magneto drive. Below this housing and in line with the magneto is the water pump, which is a large-capacity centrifugal type. Immediately below this is one of the oil pumps. The crankshaft is rather different from that of the s.v. cars, being heavier in section but without balance weights, also the journals are larger in diameter. It is polished all over. The design of the main bearings is very similar to the s.v. cars, but the connecting rods are different. Apart from being longer they are of a lighter section, being only .062 in. thick in section and drilled from top to bottom with holes varying from .375 in. to .50 in. in diameter. They are polished and balanced. The pistons are semi-domed type, having a flattened crown of 1.125 in. diameter. Their overall length is 3.5 in. and the gudgeon pins are .625 in. diameter and hollow. Inside, the piston is webbed from the centre of the crown to the bottom with 8 radial webs. Each piston has 3 rings, all at the top; two of these are compression rings and one is a scraper. There are twelve holes for oil drainage. The pistons are by Specialloid Ltd.
These engines were originally of the wet-sump type with an oil tank placed behind the engine and fed under pressure to the sump when necessary. So, as this was the original layout I will first describe it, and then deal with the modifications which were made to convert it to dry-sump. Originally the sump was a very large, deep, alloy casting, the deepest part being at the front end, and although the oil pump was below the level of oil it was placed outside the sump, oil being drawn away through a large cast outlet. From this pump the oil went straight to the back of the engine where the filters are fitted; these are built into the nearside rear bearer-arm, just as on the s.v. cars. From there the oil passed to the main and big-end a and oil pressure gauge, the bearings being fed by a gallery pipe similar to that on the s.v. engine. The camshaft oil supply was on the drip feed principle and I suggest that this oil supply came direct from the tank. It is purely surmise, but I imagine that the running pressure would probably be similar to the s.v. engines, i.e., 60 lb./sq. in. A pressure relief valve was placed just forward of the near-side front bearer-arm and on the bearer itself was located the arm of a rather neat tap for flushing the sump, which saved groping below the engine for a plug.
On each camshaft housing was a very large oil return pipe, the inlet-side pipe coming forward to empty on to the timing wheels, the exhaust-side pipe to the back of the crankcase. The oil filler was on the near-side, and a truly enormous one it was, occupying the whole of the space between the engine bearers, having a swinging lid, and probably holding about a gallon of oil itself. On each opposite bearer arm, that is, near-side front and off-side rear, there was a large crankcase breather.
As the engine is now, the oiling system is very different and perhaps it may he that it is improved, for one thing which stands out very prominently is that the oil pressure is now reading, with a hot engine, 30 lb./sq. in. at 750 r.p.m., rising to 120 lb./sq. in. at above 2,000 r.p.m. This pressure, I am inclined to think, is rather high and I feel that a maximum of 90 lb./sq. in. will be more than enough. One great change is that the camshafts are new pressure-fed and far too much oil is getting into the valve chambers for, due to slight wear in the valve guides, quite an amount of oil is arriving in the tops of the cylinders when the engine is left standing idle. A cut-off tap is provided for the supply to the camshafts, but this I think can be more of a menace than an asset, for it is so easy to forget to turn it on. Some method of cutting down this copious supply of oil will be arranged in the near future. In place of the original sump a large 4-gallon tank, placed between the dumb-irons, now carries all the oil. The tank is provided with 2 filler caps, both being in use and no doubt provided for cleaning out purposes. Oil is drawn from the tank by a pump placed so as to be driven from the train of gears which drives the magneto. The incorporation of this extra pump has meant that the radiator has had to be moved forward 5/8 in. This pump delivers oil to the filters and thence its routine through the engine is as it was originally. The sump itself is now of sheet metal and fabricated, being much shallower than the old aluminium counterpart. A pump placed below the water pump, which again is not altered from its original position, returns oil to the tank. It is from this pipe that a lead is taken off to the camshafts. A pressure balance pipe is placed between the timing case and the tank.
The carburetters are twin S.U.s of a somewhat out-of-date pattern. Most likely in the future these will be substituted by their modern counterparts. The needles are E.4s and there is evidence that the mixture supplied is very rich. As I have yet to give the car a long run performance figures are not available. Fuel is fed from the tank by air pressure, this having replaced two electric pumps, as it is not my intention to have an electrical system fitted until next winter.
Basically, the chassis is very similar to the standard side-valve, but just one or two points are worth noting. The front springs are shorter by 1 1/2 in. and the front dumb-irons are braced by a large tube which carries the supports for the front of the oil tank. The gearbox Is mounted a little farther back in the frame and the clutch is the small diameter Hele-Shaw. The rear springs are only 40 in. long in place of the standard s.v. length of 48 in. This has the effect of reducing the frame height over the rear axle no less than 4 in.
The converting gentleman of Bristol had put in a central gate and gear lever, no doubt because he wanted a door on the driving side and, although very nicely carried out, this was one of the first things to he scrapped. The old right-hand change outside the body has now been restored and, although the original parts were not available, I have very carefully copied the original designs and had the necessary parts made up. A gear lever off an s.v. car completes the conversion. In like manner I have restored the braking layout to its original design. This had been modified by divers means so that both hand brake and foot brake worked on all four wheels, and many extra levers and yards of cable were necessary. The present layout is that the hand brake only operates all four wheels and the foot alone works on the front wheels. This may horrify some modern drivers, but I can assure them that the braking operation is 100 per cent. lighter to manipulate now that the original layout is restored and stopping distances are quite as good. The fuel tank is now placed between the rear dumb-irons in s.v. fashion, the reason for this being that, although the majority of the new body (at least from the radiator to the seats) is a replica of the original Grand Prix two-seater, the remainder is a small and rather clover-leaf compartment to carry whatever we need on our travels.
This body is entirely new, no part of the old body being used. It is very lightly framed in ash and panelled in 18-gauge Dural. The seats are upholstered in green leather with Dunlopillo cushions and the top edge of the body is beaded with aluminium strip held down with brass screws in true vintage fashion. The instrument board is of 3/4-in. Honduras mahogany and polished and contains rev.-counter, clock, air and oil pressure gauges, water and oil thermos., front Telecontrol gauge and adjusting screw, air pump, ammeter, and the usual switches. The total weight of this body is under 1 cwt. with instruments, etc., and it can be lifted off single-handed. The scuttle, which has a large bulge covering the brake pedal, is detachable, which greatly facilitates the usual routine oiling of the clutch and gearbox. The fixed part of the scuttle is cowled and on these cowls is carried a single-pane, fold-flat screen. No lighting set is at present fitted. The wings will be very light aluminium, gently domed and with centre rib. They are to be suspended from the frame. A set of new 19-in, wheels are ready for a set of 4.50 by 19 in. tyres when some kind friend will help me with a permit. And so that is the restored Zborowski Grand Prix car.
I will try now to give some details or the car's history. Going back to 1922, when these two cars were first laid down, the two chassis were being prepared before the advent of the 16-valve engines. They were entered in the T.T. along with "Bunny"; actually, only "Bunny" started in this race. I have a cutting from the Autocar showing one of the chassis, which ultimately had a 16-valve engine, being assembled, but, at the time the photograph was taken, a s.v. engine was installed, the caption saying that this car was being prepared for the T.T. with s.v. engine. Later in the same year they were completed and fitted with their 16-valve engines and entered for the Grand Prix. In this race they had to give away 25 per cent. engine capacity, the capacity limit then being 2 litres. Despite this they had to comply with the weight restrictions limiting them to 12 to 13 cwt. Practice showed that their maximum speed on the course was some 94 m.p.h. and it is to their everlasting credit that they held 5th and 6th places at half distance. Zborowski, who was 6th, was the first to retire with the old magneto trouble, and after Gallop had run a considerable distance in 5th place, he too followed Zborowski. Zborowski then drove No. 15 at Shelsley Walsh, making a climb in 61 sec., but Moir, driving the second car, was much faster, climbing in 57.2 sec. After this I believe No. 15 was sold to Eyston and No. 8 remained with the firm. This was the beginning of Eyston's racing career and he used No. 15 and a track car for some four seasons, with a considerable amount of success. No. 8 was driven by Moir and Zborowski at practically all the sprint and long distance events during 1922 and 1923, Zborowski finishing second in both these years in the Penya Rhin Grand Prix.
After the Penya Rhin Grand Prix of 1928 Zborowski stayed in Spain for a further 1,500-c.c. race, this time at the new Stiges Autodrome. Once again he was against the Talbot-Darracqs. In this race Douglas Hawkes also drove an A.M., but he retired with broken valve springs. Zborowski went on to finish 3rd behind two Talbot-Darracqs.
After 1923 the car was used regularly on the road by Zborowski and remained in his possession until he was killed, after which it was sold, and it was then that I first came into contact with it. It was owned by a gentleman, whose name I forget, from Sutton Coldfield, and in those days it was basically in its original trim excepting that wings were fitted at the front and there were a battery and lights, also a shallow, fold-flat screen and hood. All these things looked rather queer, being very primitive and somewhat overwhelming this slim car. Its original colour of racing green had been replaced by the white which was a characteristic feature of Zborowski's cars. I have one or two photographs in my scrap book which I took during a visit to Sutton Coldfield during 1929. After this the car disappeared, and it was not until 1982 or 1933 that I saw in the Autocar an article entitled "An Enthusiast's Ideal," and there discovered the old car in its new guise. It was in this condition that I bought it in 1940. Whilst on a holiday tour of Cornwall in my s.v. car in 1938 I called on Hitchens and examined it, and from then until 1946 the engine had never been run.
On taking delivery, as a precautionary measure and also to cure a loss of compression on No. 1 cylinder, I decided to completely strip the engine down. This loss of compression was due to a bent inlet valve caused by a rod breaking whilst the car was in Hitchens' possession. A new valve has now been fitted and in general, with the exception of very slight wear in the valve guides, the engine is in perfect condition. It has had but one rebore and is only a matter of .015 in. oversize. The cause of the rod failure was no doubt due to the fact that Hitchens used the car with a 4.75 to 1 top gear. Since the normal top is 3.5 to 1 I fancy that the increased revs, at full speed found the rods not up to it. The car is now fitted with its 3.5 to 1 axle ratio and this should give me something over 90 m.p.h. at 4,000 r.p.m.
The following data chart has been compiled by using some of the valuable information quoted by Mr. Pomeroy in his "Milestones of Speed" series published in the Motor, which has proved most useful.
The remaining number of 16-valve A.M. engines is now, to the best of my present knowledge, a mere 4 only. Three of these are in England, and the fourth is in Amsterdam. Not very long ago I received a most interesting letter and set of photographs from a Mr. Loyens of Amsterdam telling me of the existence of the famous car which was sent to Switzerland in 1925. Fortunately, it is still in good hands and will be preserved. For some considerable time, Mr. Loyens tells me, it was the 1 1/2-litre champion of Switzerland and remained in the hands of its first owner right from 1925 up to the time of the German occupation of France. The three remaining engines in this country are:
1. "Razor Blade."
2. Ex-D. B. Tubbs chassis.
3. Ex-Zborowski 1922 G.P.
It may be that two or three more engines are in existence as probably three were made for racing motor boats, one in particular being Major Johnson-Noad's "Miss Betty. I believe there is a photograph of this boat in an early Motor Sport (or Brooklands Gazette as it was in those days).
I have been asked by one or two of the local owners of B. & M. cars to make a few notes on their cars, but this must be left for the future, when I hope to have compiled sufficient data to give a complete history and review of the activities of B. & M.s from 1914 up to 1925. This will include a good deal of personal history of as many of the cars as I can trace, and Mrs. Martin has most kindly consented to assist with whatever missing data is available. It is therefore important that all those who own B. & M. Astons, and all who have owned these cars, will contact me and let me have as much information as possible. Many have already done this, I know, but there is still much to know of these most excellent motors.
Data for Grand Prix Aston-Martin, 1922
Number of cylinders ... 4
Bore ... 65 mm.
Stroke ... 112 mm.
Total swept volume ... 1,487 c.c.
Number of valves per cylinder ... 4
B.H.P. ... 55
B.M.E.P. ... 106.5
Piston area ... 20.6
B.H.P. per sq. in. of piston area ... 2.67
Max. piston speed, ft. per min. ... 3,307
Stroke bore ratio ... 1.72
Inlet valve area ... 7.7
Inlet valve area / piston area ... .0374
Max. torque, lb./ft. ... 64.19
Compression ratio (approx.) ... 6.56 - 1
Carburetters ... 2 S.U.
Meedles ... E.4
Magneto ... 1 Bosch ZF4
1st ... 9 - 1
2nd ... 6.5 - 1
3rd ... 4.5 - 1
4th ... 3.5 - 14
Fuel ... Alcohol
Oil ... Castrol R or Aero Shell for Engine Gearbox and Rear Axle
Total dry weight of car without Electrical equipment .... 12 cwt.
[Those readers who are particularly interested in the B. & M. Astons may like to know that, apart from the above, Motor Sport published a long article by Mr. Ellis on the s.v. cars in May, 1943, and that a description of one of these cars appeared in the issue for April 1938. Other references will be found in the issues for August 1943 and May, 1944. — Ed.]