The Rotary Valve Two-Stroke Engine.
Ian Ager.
The two-stroke that we know of today was invented by an English man by the name of Joseph Day who was born in London in 1855, in 1873/74 he trained as an engineer at the School of Practical Engineering at Crystal Palace in London. At the end of 1874 he then moved to Bath to work for Stothert and Pitt a company manufacturing large cranes for the docks and railways.
My interest in this subject came about when I was invited to a friends garage to view his collection of vintage/veteran motorcycles, one machine that caught my eye was a little 1922, 268cc Sun motorcycle which was a two-stroke with a rotary valved inlet. This led me into, who designed and built the first two-stroke engine with a rotary inlet valve?
In 1878 along with a J W Lampard they started a company, an iron foundry in Bath,making cranes, mortar mills, compressors, and various other things but most of his work came from his old employer. By 1889 he was working on a petrol engine of his own design that would not infringe the patents that Otto had on the four -stroke, and Dugald Clerk a Scot born in Glasgow who in 1881 had patented the design of a twin cylinder two-stroke engine, this was where one cylinder was used purely as a charging cylinder for the other one, (this would have been very similar in type to the split single design that the howling German DKW`s used in their racing bikes before WW2 and the Puch motorcycle company made in the 1950/60`s.)
The 'Sun' Two-stroke Motorcycle.
Split piston two-strokes were not a new idea. Garelli introduced the concept in 1912, and Puch had been building simple split-single engines (sometimes referred to as “Twingles” after they were marketed under that name by Sears in the 1950s) since 1923. Puch in fact won the 1931 German Grand Prix at the Nurburgring with a liquid-cooled and supercharged 250cc split-single ridden by Swiss rider Elvetio Toricelli, something that may have been a significant influence on DKW's subsequent racing programme.
In 1892 Joseph Day applied for and was granted the patent on the engine it came to be known as the “Valveless Two-Stroke”, in the patented design it had two flap valves, one in the crankcase for the inlet, (similar in principle to the reed valve on today’s two strokes) and one in the crown of the piston, One of two known original Joseph Day engines is in the Science Museum in London, and the other one in a Museum in Germany.
The Valveless Two-Stroke Engine
In October of 1892 Frederick Cocks came up with the idea of allowing the skirt of the piston to control the opening of the inlet port, and the removing of the valve in the piston head by charging the cylinder via a transfer port in the cylinder wall, giving rise to the two-stroke engine that we know of today. The piston was cast in iron with a bridge on the crown to deflect the charge up from the transfer port to the top of the cylinder away from the exhaust port which was directly across the cylinder.
Frederick Cocks who was a Steam, Gas and Electrical engineer, who was living in Bath, if working for Day I cannot find any evidence but he applied for the patent for the third port (transfer) but the patent was assigned to Joseph Day. It would have been the custom and practice that all the inventions made by an employee of the company, the rights of any invention would be transferred to the employer, this practice is still current in many companies even today.
Joseph Day was made a director of the Western Counties Steam Bakeries and Milling Co. when it was formed, and the production of the engine only played a minor part in the output of the Bath company, at this time the major production being the manufacture of bread making/milling machinery of the Western Countries Steam Bakeries Co. most of which was sold in the USA.
The fluctuation of the wheat prices in the USA lead his company into bankruptcy and closure in 1893, and lawsuits were filed against him in England. At the time Joseph Day was in the USA trying to sell his US patents in order to raise money to save the Bath company, even the British Treasury solicitor at the time tried to have him extradited from the USA to stand trial. When at last he did stand trial in 1894 the jury found that Day had no case to answer and he was acquitted.
The production of the engine during this period was undertaken by Llewellyn and James company, about the same time he sold the patent rights to the Valveless Gas Engine Syndicate. But later in 1898 he was involved in legal action with them over the rights to the engine, claiming it was for the first version of the engine (with flap valves) not for the later type.
In 1906 discharged from bankruptcy he started the Day Motor Company in Barking and later in Putney London making the engine to which he still had the patent rights. In 1916 it has been claimed that the Valveless Two-Stroke company was taken over by the Sun Motorcycle company and certainly in their brochure for that year detailed a lightweight motorcycle fitted with a VTS engine with a separate oil feed and a two speed cog box fitted with a cork clutch and they continued to use these engines until the mid 1920`s.
The SUN VTS 1916
It has been reported that in the 1921 lightweight T.T. (engines up to 350cc) Sun entered two 268cc motorcycles that finished 9th and 10th, (B. H. Norris and M.V. Bishop) when searching the I.O.M TT records for that year no trace of an entry being made for the Sun motorcycles can be found. But in 1922 the Sun Motorcycle Company entered two motorcycles in the lightweight TT (this year for engines up to 250cc only).
This picture shows the 1922 Sun TT team from L to R: W J Lord, Gus Kuhn, unknown (Is it Mr. Parkes, the boss?), M Bishop & unknown. [Thanks to Bill Snelling for this info]
They reduced the engine size down to meet the 250cc limit but in the race they both suffered from severe vibration problems from lightening the reciprocating parts that they both split the petrol pipes in the race, and with rags tied round the lines to stop the leaks finished 12th and 13th, at an approximate race speed of 37mph, on a TT coarse of cobbles, Tarmac and dirt roads complete with potholes.The winner was a G. Davidson riding a Levis with a speed of 49.89mph. After this the Sun Motorcycle Company withdrew from racing. It is possible that these engines were fitted with the rotary valve inlets, as a patent was granted to John Duffey in 1922 for the invention of the rotary valve but again assigned to The Valveless Two-Stroke company, was this still trading under the VTS name owned by Joseph Day or was the Sun Motorcycle company trading under the VTS name?
A couple of years later it was reported that Kaye Don lapped the Brooklands circuit at 70 mph on a similar machine quite an achievement being no more than a push bike with an engine. All further development of the two-stroke engine was now being undertaken in Germany. Adolf Schnurle in 1926 developed the loop scavenging system of filling the cylinder. And after WW2 the DKW company who in 1951 were racing a 3-cylinder 350cc machine complete with an expansion chamber exhaust system design by Erich Wolf.
In 1949 Daniel Zimmermann a privateer road racer modified a IFA motorcycle race engine by fitting a rotary inlet valve to the engine and promptly showed the works machines the way home.
In 1952 Kurt Kamph the racing manager of the IFA racing team had by then fitted the Zimmermann rotary valve inlets to the works engines and copied the Wolf design of expansion chamber to suit the teams IFA racers, Walter Kaaden succeeded Kurt Kamph as the race manager of the IFA team in 1953 and the company was then renamed MZ. The development of the two-stroke engine with Walter Kaaden is now well documented with the Ernst Degner's move from East Germany to Japan.
Back to the photos the Sun Motorcycle that started this write up.
No 1 - The standard engine as fitted circa 1920`s
No 2 - Modified with the rotary valved inlet
No 3 - Rotary valved engine with the second inlet. 
(see note below)
No 4 - Sun Vitesse Motorcycle 1923, ( belt drive, with no or very little braking, fancy riding that at 70 mph.
The barrel of the engine is that as fitted to the standard engine, but the carburettor has been replaced with a body of a carburettor but fitted with a solid slide, this can be opened-up to allow extra air into the engine by a lever on the handlebars. This, I am told by the owner, is when opened is just like a two-stroke coming on the powerband. The only explanation I can give for this is the Amac carburettors of the day only had one jet and a slide that opened it up with no other forms of metering, e.g., pilot jets, needles or slide cutaways. The jet would have only be suitable for a certain rev band, so when above that rev band the engine would have been running very rich, Therefore to lean it out they admitted more air through the dummy carburettor.
Ian Ager
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The Scott motorcycle company two-stroke engines adopted the “Day” piston type porting and the bridged pistons, and used them until their closure in the 1950‘s. In 1911 to 1913 Scott entered the Senior TT with engines ?tted with a gear driven rotary sleeve ?tted behind the engine which controlled both the inlet and transfer ports with great success but then dropped the idea.
The Dot motorcycle company also entered the 125cc TT in 1952 with their engines ?tted with a chain driven rotary drum between the barrel and carburettor, very similar to Scott’s, they entered three machines one of which blew up in practice, one retired on the ?rst lap whilst the other lasted the race and ?nished in tenth place.
After this I could not ?nd any further information of a motorcycle company in England using the rotary valve engine or any further development of the two-stroke engine.
Rotary Valve Two-Stroke Engine
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