The Hotchkiss V Twin Engine, research notes by Dave Daniel

Hotchkiss History and Notes


Dave Daniel – – – March 2010

When I bought my BSA Three Wheeler back in 1972, I found it described as having “the Hotchkiss Engine”. There was no obvious Hotchkiss connection with BSA and Hotchkiss was a French company. The only common feature seemed to be that both were arms manufacturers who had become involved in the car industry.

The engine was very strange. It had very highly advanced design features, coupled with other features which were quite old-fashioned and it seemed to have no commonality with any other BSA engine, or for that matter any other engine of that period. There were stories that it was based on using up old WW1 aircraft engine cylinders and a host of other myths, some more improbable than others.
My own observations suggested that the engine did, strangely, have some aeronautical connections and was probably designed by someone who’d been involved with aero engine design in WW1, but there the trail ran cold. The BSA design team was involved in gun design, not engines, and so were Hotchkiss.
Eventually I fell on information which threw light on the engine and revealed an interesting story spanning the breadth of the early motor industry.
The following notes on the Hotchkiss Company are largely taken from “The Flatnose and Bullnose Morris” by Jarman & Barraclough. I am particularly grateful to a member of the Rolls Royce Heritage Trust – Mr David Williams, who in discussions with Peter Cook, our Club Chairman, at the 1999 National Rally was able to provide unpublished information forming the key to solving the problem. The information gleaned from Harald Penrose’s works on the British Aviation industry and publications of the Rolls Royce Heritage Trust concerning the Coventry Parkside site, and Armstrong Siddley have also been extremely helpful.


Hotchkiss et Cie started life in the Franco-Prussian war in factories at Saint Denis and Levallois-Perret in the Seine district of France. The story is that when it looked like the factory at St. Denis might be overrun by the Germans in the Great War, production was hurriedly transferred to a new factory in Far Gosford Street, Coventry. On the face of it this appears a simple story, but there are some aspects which remain intriguing: St. Denis is in the northern suburbs of Paris. Levallois-Perret is also in the northern suburbs, about 2.5 miles South West of St Denis. The Germans did come near to Paris in the first few weeks of the war, but following the Battle of the Marne in September (the war started in August 1914), the Germans were driven back to lines which remained static until the end of the war. Had Hotchkiss needed to move they would have needed to move both of their factories, and extremely quickly, to avoid the anticipated fight for Paris. It seems to have been in the late summer of 1914, but as it was in hasty flight from the German guns, they had no time to build their own factory, furthermore, following the stabilisation of the lines in 1915, any further relocation was probably abandoned.
The Hotchkiss factory in Far Gosford Street is still partly there today. For those visiting Coventry, a trip around the city ring road will lead past the building outside the ring road between the A444/M69 and A45 turnoffs on the North East corner. The building was for many years government offices, but was recently sold to Coventry University, and redeveloped, ironically as the “Morris” building. It now sports two additional floors on the roof of it’s original 4 story brick factory office block, characterised by their white Grecian pillars and the new arched roof. The building is sometimes referred to as a Government building, and this name seems to precede its office use, suggesting that Hotchkiss may have taken over or leased an existing factory. The factory itself was to the rear of this building with an annexe opposite the main frontage and was subsequently demolished.
In any event by the end of the War Hotchkiss were well established in Coventry, with a full order book for arms. It is said that the factory had produced 50,000 machine guns.
Following peace, however, orders dried up. The Works Manager, a Mr Ainsworth, had modern production facilities and a good engineering team, but no work. The rumour apparently “got round” that Morris was looking for engines, and Ainsworth and M.Benet, the Managing Director from Hotchkiss in France, were at Morris’s door to make an offer to make engines, to Morris’s designs if preferred, as Morris had acquired the manufacturing rights to his American Continental “Red Seal” engine. Hotchkiss offered to copy the engine and did not ask for any deposit or any “up front” funding or tooling deal. Even though Hotchkiss had never reportedly made an engine, Morris had a good deal, with no financial commitment, and if things went wrong the Continental “Red Seal” supplies would have presumably just carried on. Perhaps this indicates how desperate for work Hotchkiss actually were. Hotchkiss produced samples in July 1919, and production started in September 1919. Bearing in mind the War only finished in November 1918, this was rapid progress.
V-twin owners may wish to note that the Continental engine had always suffered clutch slip from oil leaking past the rear main bearing seals. The Hotchkiss engine was designed with a two plate wet cork clutch, attributed to Morris himself as a solution to the problem, and the copy was so close that the complex oil seal, no longer needed, was retained. The BSA FWD cork clutch, retained throughout production of the BSA FWD car range, is a close copy of the Morris design. (Editor’s note: The clutch plates in which the corks are embedded were identical in size and design excepting that the Morris version was in mild steel, often with “MOWOG” stamped on them)


Fred Green (Born 1882) was a Daimler Man, and in Coventry in the early years of the Century that was a title of some prestige. Daimler Men always went to work in shirts and ties, no matter what their job. They always looked neat and tidy, and saw themselves as a step above other workers in the Motor Industry, after all, only their cars were good enough for Royalty……. Fred Green was a graduate taken on by Daimler and earned a reputation working in their engine design department in the 1900’s He is described as a tall, hook-nosed man with a rather abrupt manner and a tendency to talk with his head held back and glancing down his nose. He later appears to have gained respect for his expertise, although his mannerisms may have counted against him on occasions.
In 1909 Fred Green met Mervyn O’Gorman, who had been newly appointed as Superintendent of Aeronautical Work at Farnborough, taking over a balloon shed and airship workshop. The discussion ended with Fred Green being offered the post of Chief Design Engineer at what was to become the Royal Aircraft Factory at Farnborough. This was a good move for Green. Daimler were short of cash for investment, having struggled free of their early inauspicious beginnings as Harry Lawson’s empire and only after their purchase by BSA in 1910 did they have a secure financial backer.


When Fred Green went to Farnborough in 1909, he acquired some old sheds used for balloons and a remit to establish aeronautics for military use. He set out to establish a government research centre and factory capable of developing viable aircraft designs and manufacturing them. In doing so he collected a team of like-minded engineers and by the outbreak of war had designed and produced the BE2 – an aircraft which was quickly outclassed, but was at least stable and reliable by the standards of the time.
During the War, Green and his team continued at the Royal Aircraft Factory at Farnborough, their last design being the SE5 fighter, which was acknowledged by many as one of the best allied fighters of the war. One area of design which seems to have focused attention was the development of a radial aero engine to replace the prevalent rotary ones. The factory came under increasing criticism for inefficiency by commercial manufacturers and despite the continuing conflict, the Government decided to close the factory in 1917, putting the design team out of work. Their demise was filled by private aircraft companies who had produced a proliferation of designs which could be produced faster, but perhaps at the expense of careful testing, although British pilots who found the resultant aircraft difficult to fly rarely seemed to come back to complain!


John Siddley (born 1866) is described as a small and fiery individual, perhaps not without good cause. From being a champion cyclist for the Humber Cycle Co he had joined the design team, and then moved to a career in tyre manufacture. His interest in cars around 1900 led to him selling his interests and in 1902 formed the Siddley Autocar Company, badge-engineering French Peugeot cars, and was successful enough for an offer to be made for the business by the Wolseley Tool and Motor Car Company, after Siddley asked them to build engines to his own design for his company in 1903.
Wolseley subsequently made cars and buses badged as Wolseley-Siddley until 1909. The relationship was not always easy, as Siddley fell out with the Wolseley Designer and Works Manager, Herbert Austin. The two engaged in a competition to build the best car, and Siddley reportedly won, although Austin accused him of cheating, and left after a row in 1905 to set up his own business at an old printing works in a little known suburb of Birmingham, known as Longbridge.
Meanwhile, the Deasy Motor Car Manufacturing Co had been founded in 1906 by Captain H Deasy. Captain Deasy had a controlling interest in the Swiss Martini car company. The Company took over the factory and land of the Iden Car Co, which was in receivership in Parkside, Coventry. The site included premises leased to the Velox Motor Works, the Maudslay Motor Co and a small chocolate factory.
Deasy got off to a very shaky start. Early cars were unreliable and prone to breakages even by the standards of the time, but in 1909 John Siddley joined the company as General Manager and by 1910, cars bearing the name “Siddley-Deasy” were being produced and started to earn a reputation for quality and reliability. Most of the parts were manufactured by suppliers, the firm being primarily an assembler.
The engines were Daimler’s. In 1912, a further wholly-owned company was established by the now Siddley-Deasy Car Co called Stoneleigh Motors Limited. This firm was to offer light cars and commercial vehicles, although very limited production was apparently undertaken, the company finally disappearing with the onset of the Great War in 1914.
With the onset of war, Siddley-Deasy started to take on engine production, building engines designed by the Royal Aircraft Factory at Farnborough – by Fred Green’s design team. Production took off in 1915 and the company expanded, taking over more of the Parkside site.


The closure of RAF Farnborough was welcomed by many aircraft manufacturers who were now free to develop and sell their own designs, but Siddley saw an opportunity and Major Fred Green, his new Protégé John Lloyd – a stress engineer, and Sam Heron, one of the engine design team, joined Siddley-Deasy. They brought with them work on developing air-cooled radial engines and the outline of a replacement for the SE5A fighter eventually known as the Siskin. Fred Green is reputed to have personally completed the drawings in a room over a Coventry laundry shortly after joining the company – office space was at a premium!
It was a good deal for Siddley. Not only had he got a respected design team, but he’d also got a huge amount of free development work on the next generation of aircraft and engines.
Siddley had been closely associated with Vickers Armstrong during the war, and in 1919 the Company was merged with Armstrongs, the outcome being Armstrong Siddley Cars, Managing Director John Siddley, and the Sir W G Armstrong Whitworth Development Company Limited, the latter rather grandly named company being housed in a small shed on the London Road in Coventry and intended to be the centre of aircraft production. Green and his team appear to have remained at the Parkside works and ran both car and aeronautical design.
By this time, whilst car production was starting to climb, aircraft work was in the doldrums. There was a surplus of military hardware from the war, and the civil aviation business had not yet been invented. Almost all flying up to this point had been in combat. The design team in particular appear to have found themselves twiddling their thumbs.
One project undertaken was the design of a cinema film projector, which perhaps shows the desperation to find opportunities. The country was bankrupt after the war and wages were cut by employers year on year to seek profitability.


At around this time, Hotchkiss appeared on the scene from their premises just around the corner. Hotchkiss were in a stronger but more vulnerable position. They had a good contract with Morris for all the engines they could make, but they seem to have justifiably been uneasy about having all their eggs in one basket. The idea they came up with was to build a light car engine of their own and sell it alongside the Morris Contract. There was only one problem. They’d never designed an engine before.
There seems to have been an approach to Armstrong Siddley to design a light car engine for Hotchkiss, or at least to give assistance, although how this came about is unclear. In any event the Siddley design team set out to design the engine.
Most of the Siddley car engines up to that time had been bought in from other suppliers – many were from Daimler, and the firm’s designers would have had little or no automotive engine design experience at that time. They did however have considerable experience at designing and building aero engines, and their old RAF research into air-cooled radial engines was off the shelf and being dusted off. An air-cooled Vee Twin must have seemed the safest and most familiar route to choose. Valve gear enclosure was said to be based on the design of a pre-war Swiss motorcycle engine (An old Deasy connection?).
Initially two experimental engines were built, one being fitted to a 1914 Morris Cowley test vehicle and the other used on the test beds.
The strong contender for the rather advanced “top end” design of the engine seems to be Sam Heron. Siddley and Heron fell out in 1919 over Siddley’s interference in engine design, and Heron left for Wright’s in the USA. He was replaced by S M Viale – an engine designer who had worked for Gwynne’s making Clerget rotary engines during the war, and had experience of alloy piston and head design. Not much is known about him, but he seems to have been able to avoid Siddley’s interference or divert it. Heron went on to be involved in much of the radial aero engine design at Wright’s throughout the 1930’s and 1940’s, but that is a separate story.
Much of the work on radial aero engines was not wasted. Armstrong Whitworth went on to create a range of engines based on the Farnborough design work in the 1920’s and the cylinder head design of these bears a strong resemblance to the Hotchkiss Vee Twin unit. Heron’s work in the US for Wright’s also reflects the early work at RAF Farnborough and the design of the Hotchkiss Vee Twin engine.
Siddley also went on to fund the development of a light car of his own, under the old Stoneleigh name. This too had an air-cooled vee twin engine but of a totally different design. By this time Sam Heron had presumably left and the design team started out from scratch. Siddley’s heart was not in the Stoneleigh car, and like others it succumbed to the Austin 7.
The creation of two Hotchkiss engine prototypes was publicised in the motoring press and the old “narrow track” Morris Cowley used as a test bed seems to have been touted widely in the industry and used for test drives by the motoring press. At least one substantive press article survives praising the engine’s performance. This left Hotchkiss one problem. Morris was clearly not going to buy the engine, and they couldn’t afford to make a whole car themselves, so who could they sell the engine to?
A round of publicity led to some small sales but the biggest interest was expressed by BSA, who had dabbled in the Edwardian car market themselves alongside bankrolling Daimler and were keen to re-enter the market. The resultant light car was the BSA TB10 tourer. This was a pleasant light car incorporating the “Hotchkiss” engine, cork clutch and Morris gearbox all built by Hotchkiss, on a chassis mounted on four long quarter-elliptic springs designed by BSA/Daimler.
The car performed well and competed successfully in a number of trials. Initial production seems to have moved to the Daimler works and around this time BSA built a new factory in Small Heath, Birmingham which it called it’s “car factory”. The site is now an ASDA supermarket but was for many years a Chrysler parts warehouse. Their plans however were soon to be thwarted.


By 1922 Morris had started to acquire some of his suppliers and build a single large business. Hotchkiss were largely dependant on Morris’s orders, but were also making the V-twin engine for BSA, and another engine for a Scottish firm called Gilchrist. Some armament manufacture was also continuing.
Morris was planning a large increase in production, and it seems that Hotchkiss’s capacity and interest in diversification was limiting these plans, so for a number of reasons Morris made an offer for the plant, and by May 1923 he owned it. It had reportedly cost him £349,423. Negotiations had apparently been going on for some time, with one motor trade journal reporting that the new company would be called Morris-Hotchkiss Limited as early as January 1923.

It is reported that at the Eighth Annual Dinner of Hotchkiss et Cie in February 1923, Morris announced it would be called Morris Engines Limited. (This incidentally puts Hotchkiss’s move to Coventry at 1914). It probably wasn’t the most popular after-dinner announcement.
Mr Ainsworth, the Works Manager, stayed with Hotchkiss and moved to France where he became involved in the successful Hotchkiss car marquee. Mr F.Wollard, from E.G.Wrigley & Co Ltd was appointed Works Manager, and under him all existing contracts, other than those for Morris, including some residual gun contracts, were completed and terminated, and the company went on to increase Morris engine production and eventually moving to larger premises in the North of the city, where it remained until closed as part of the cut-backs of the British Leyland consortium in the 1980’s.


The formation of Morris Engines left BSA without an engine for their new car. Some larger Daimler-derived engines were tried but apparently without much success. In any event the previously mentioned Herbert Austin had put the cat amongst the pigeons by introducing the Austin Seven. With a diminutive price and a four cylinder engine to boot BSA, like many other manufacturers, were trapped and priced out of the market, and the model ceased production. Some efforts were made to continue using other larger Daimler-derived engines but without much sucess. BSA did however manage to hold onto the design rights for the Hotchkiss Vee Twin engine which were stored away in the archives. Peter Cook has uncovered entries in the minutes of BSA meetings suggesting that a licence fee was paid to Hotchkiss throughout the 1920’s, presumably for the continuing rights to the design.


In 1929 BSA re-entered the car business again by launching a new three wheeler car to compete directly with the Morgan.
The design boasted a redesigned “Hotchkiss” Vee twin engine mounted in a car-style chassis driving front wheels via a new FWD 3 speed gearbox based on the general layout (but no more) of the Alvis FWD car. The car outclassed Morgan’s 2 speed trikes and included many features as standard that Morgan classed as extras, such as an electric starter.
The payment of licence fees for an engine you weren’t using must have been quite an embarrassment, so hauling the Hotchkiss engine out of the plans and using it would have been a good tactical step, and ensured work for the BSA design office. Perhaps this explains why BSA did not just use a motorbike engine like Morgans. It must be also said that the Hotchkiss engine was a 90 degree Vee Twin with inherently better balance than a standard motorbike 60 degree Vee Twin.

When the Vee Twin trike was constructed in 1929, the engine, whilst being very similar to the original, had been extensively redesigned by BSA, suggesting that whatever rights they had to the design, they probably had never had much in the way of patterns or tooling, and took the opportunity to re-draw the design, incorporating BSA standard parts and adapt the engine layout.
It seems that the BSA design team had little real knowledge of the engine’s heritage nor its real capabilities. In the three wheeler form, the arcane induction manifold fitted seriously compromised the engine’s power and strangled it. All of the inclined overhead valves, hemispherical combustion chamber, aluminium pistons and wide valve overlap timing – ideal for a high performance engine – were effectively negated. Later enthusiasts found that just fitting twin carburetors and abandoning the single updraft Solex took the top speed from a very respectable 60mph to a white-knuckle 85mph or more, which perhaps is a graphic indicator of the restriction on the engine and its aspirations for powered flight!
It may of course be that BSA chose not to explore the engine’s performance capabilities because of fear that the rest of the engine would not stand up to such power, but there seems to have been no attempt to design these features into BSA motorbike engines, designed by the same BSA design team.
Although the BSA Vee Twin three wheeler sold well in comparison to Morgan, which it massively outsold in the 1930’s, BSA were clearly moving towards a four cylinder alternative which offered a smoother and more acceptable ride and continue to upstage Morgan. There is some surviving film footage from 1932 briefly showing a BSA trike on the production line with a 4 cylinder sidevalve engine – apparently a works test vehicle. By 1933, the new “long bonnet” trike range was being sold, with the choice of the old Vee Twin or a lightweight 4 cylinder water-cooled sidevalve design.
The Vee Twin ran in production from 1930 to 1936 when the last few were sold. By that time the market for three wheeled cars had collapsed as a result of taxation changes, and BSA were firmly involved with 4 cylinder, 4 wheeled machines, and so came to end a fascinating engineering story.


The Hotchkiss engine has a hemispherical combustion chamber with inclined overhead valves, and on the early engine there was clearly provision for two spark plugs, one on each side of the head, like an aero engine. In the later light car engine, only one plug was fitted, and in the trike engine the position of the plug was altered to sit between the valves rather than at the edge of the cylinder. The bottom end was based on motorcycle practice with a roller-bearing big end on a built-up crankshaft. The oil supply was a low pressure “squirt and hope” system with a regulator dispensing an oil supply directly to the cylinder walls and pistons. The pistons had a bottom skirt ring to contain the oil next to the piston wall on the upstroke. Later modifications included an extended jet squirting oil at the big end as well as the timing gears. The valve timing on all of the twin variants appears to be the same, and incorporates large valve overlaps, as in a modern car. In fact the valve overlap is larger than some moderns, and would equate to a tuned modern engine.

Inlet Exhaust
Opens before TDC Close after BDC Open before BDC Close after TDC
16 degrees 64 degrees 62 degrees 26 degrees

For its day this arrangement is remarkable. You have to remember that BSA was making motorbike engines with simpler side valves into the 1930’s and even the BSA 4 cylinder engines are relatively conservative in terms of head design. Fred Hulse, and presumably much of the BSA design team were busy with munitions in the Great War. His name is apparently associated with several patents to do with guns. All of the V-twin head design points to an engine designed for high performance – yes, you may scoff at its 4.5:1 compression ratio, but early fuels were not good and all air-cooled engines have low compression ratios, because of their poorer cooling. The last VW air cooled flat four engine, made for their Transporter van, has a compression ratio of 7.4:1, compared with an “A” series-engined Rover Metro with compression ratios of between 8.4-10.3:1 (the highest compression ratio was for the Economy HLE variant). Vintage engines were sometimes prone to valve burning and breakage, as a result of poor metallurgy and unleaded fuels. Perhaps this also explains why having designed a high performance engine, its potential was immediately choked by the complex induction manifold used on all of the twins.
Perhaps Sam Heron’s own words explain the design more fully:
“The only important job I can remember we did was an air-cooled twin cylinder 90 degree engine, for a light car. This was done for Hotchkiss et Cie, a firm in Coventry. The Hotchkiss factory had been established during World War 1 to make machine guns for the British. The engine had cast iron cylinders with the cylinder and barrel in one piece. The valves or were inclined at a very considerable angle in a hemispherical combustion chamber, this being a very similar to later aircraft engine designs. The valve gear was enclosed and lubricated. The valve gear lubrication was supplied by the crank case breather, breathing being brought up the push rod housings into the rocker boxes and then vented through the rocker box covers. The exhaust ports were on the front of the cylinder and the valves were fore and aft in each cylinder. The enclosure of the valve gear was definitely

copied from a Swiss motorcycle engine, of which I was aware of prior to 1914. I am not sure if the Swiss used crank case fumes to lubricate the valve gear. However, to the Swiss goes the credit for this feature, which later became a standard practice on aircraft engines. On aircraft engines, a course, we did not rely on crankcase fumes (?alone?) to lubricate the valve gear. Incidentally, the outlet for the crankcase fumes up the pushrod tubes was the only breathing supplied to the crankcase. The engine was manually started, and on the starting crank was on the camshaft. A decompressor was fitted which lifted in the exhaust valves slightly when starting. Starting it was very easy by swinging the crank: I believe the decompressor was automatically released when the crank was released. An attempt was later made to obtain starting with the starting crank on the crankshaft but this proved impossible. If one got one cylinder over top of dead centre on the compression stroke, the crankshaft ran away with one. Solid aluminium Pistons were of course that it, since there they were the only piston type I knew that could be cooled in an air-cooled engine. Later, this was to be the cause of considerable controversy, as will be discussed. Manufacture of the first experimental engine started at a Hotchkiss. Surely thereafter Green closed the consulting business, and I was transferred to Hotchkiss.”
Perhaps the final comment hints at the bad feeling between Siddley and Heron which led to his move to the USA, and suggests that for a period of time, Heron continued to work at Hotchkiss on the development of the engine. The use of “crankcase fumes” to lubricate valvegear is something Sam Heron seems to focus on. It didn’t work. The BSA “Hotchkiss” was liberally equipped with greasing points on its valvegear with the manual requiring the greasegun to be applied every 25 miles!

D R Daniel


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