Home made motor cycle engines

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John_Stevenson
Posts: 531
Joined: Sun Dec 22, 2002 9:51 am
Location: Nottingham, England.

Home made motor cycle engines

Post by John_Stevenson »

Nor sure how this sits on the group.
They are home made but full size. Anyway I though I'd share them with you.

A very dear friend of mine, Dennis Jones who is now in his 80's built a series of motorcycles that started in the war years and went on until 1959 when he lost interest.
Trained as an engineer at Rolls Royce Derby , Dennis spent a lot of time working on the RR Merlin.
During the war he decided to build his first bike.
Not a simple two stroke as many would start on but a 500cc flat four across the fame supercharged two stroke.
It took him just over two years to build this. No mean feat in wartime and when you consider he made the all patterns for the engine and gearbox and wheels as well. It was a complete bike from start to finish. His own frame, a unique design of wheels and brakes for the day and also incorporated shaft drive.
The only parts he didn't make were the supercharger, carburettor, magneto's, gearbox internals and the final drive gears which were all propiatory parts.

The engine although a two staroke followed four stroke practice in that it had a pressure fed oiling system. Being supercharged it didn't need to use crankcase compression. The rest of the engine followed current two stroke design with deflector top pistons and 'L' shaped dykes rings [ also home made ].
Transmission was by a flywheel holding Norton clutch plates in a basket. The rest of the transmission was also Norton mounted in Dennis's own gearbox casting.
Final drive was by a shaft and universals to an Austin 7 crown wheel and pinion.

The brakes were unique in their build up and efficiency for their time. Both front and rear were identical at 7" diameter but both had 3" wide linings and were twin leading shoe. Up to this time no brakes had been made as powerful as these.
The design placed the shoes exactly on the centreline of the wheel so there was no torque reaction when braking. Something that was never repeated until double sided brakes came along.

I've attached a picture of the flat four. This is the only picture of the complete bike that exists. Dennis is the one pointing out the features.
He later went on to build five 250cc DOHC four strokes starting in 1948 and going up to 1953. All more or less the same these were capable of running at 11,500 rpm.
He then used two of these to make an across the frame 500cc four cylinder round about 1955 and finished up with a 250cc single cylinder 4 valver in 1959.

If this isn't in keeping with this group please say so or I will carry on at a later date and show the other engines.

John S.
John_Stevenson
Posts: 531
Joined: Sun Dec 22, 2002 9:51 am
Location: Nottingham, England.

Re: Home made motor cycle engines

Post by John_Stevenson »

2nd Instalment.

Just a pic as an attachment and short description.
This is the timing side of one of the 250 twin DOHC engines.
All the drive is by gears to the oilpump, lower, the magneto and the cams. All the idler gears are on double ball bearings and the large idler has a hunting tooth to even wear out.
There is no adjustment for any of the gear centres. The backlash in the hunting gear where the heads split is controlled purely by the machining tolerances. No head gasket is fitted, it's a ground joint.

John S.
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