PISTONS & COMPRESSION RATIO'S

This is a BSA B40 scramble piston

There are a number of classic machines that are fitted with pistons that are increasingly more difficult to obtain. In such cases I can find a similar piston, sometimes from an automotive catalogue and modify it to fit. In some instances this is a good opportunity to raise the compression and enhance the performance without affecting reliability at the same time.

A typical example is the Norton engine above. This has been fitted with a BSA B40 scramble piston giving a compression ratio of 10 to 1. A 16H side valve piston can be shortened and re-shaped to go as high as 9 to 1.

Lightweight Aluminium Barrels for Long and Short Stroke Engines

The plan was to initially produce three engine sizes.
84mm X 90mm. This was a Norton Pre-war experiment.
85mm X 88mm. This is the famous BSA Goldstar dimentions.
86mm X 86mm. This is What is commonly refered to as a square engine, that is the bore is the same size as the stroke.
I have now realised that the Classic Trials enthusiast does not want a hi-reving short stroke engine.
The fourth variant will be a copy of the famous 500T barrel with dimentions of 79mm bore to be used with a standard 100mm stroke crank.
The most popular conversion is to fit my 87mm barrel to a Mod 50 engine. The capacity then jumps from a 350cc to a 520cc.

HERE IT IS, A 600cc ES2 Conversion.

This is the new 87mm piston and barrel This 87mm piston and ally barrel will make your ES2 into a short
stroke 600cc engine. It is not a D.I.Y. bolt on kit because I
need to re-balance the crank to the weight of the new piston and
machine the rebate in the cylinder head to fit the new barrel.
The machining leaves a squish band.
Couple this with an almost flat piston crown and you get a full
600cc short stroke engine with higher compression ratio and better
breathing.
Your ES2 will then be capable of pulling a higher gear with 80 mph cruising.

This is the first barrel produced

Early indications are showing a weight reduction of 8lb.
The Iron Norton barrel weighs in at 14lb or one stone.
My aluminium barrel complete with liner weighs 6lb.

Same barrel, change of angle

This shot shows the flanged liner that is shrunk in at 490 degrees. After being allowed to cool down to room tempreture the bore is then machined to the required size. This is a short stroke barrel and can be bored to 84mm, 85mm or 86mm. The maximum size permissable using a larger sleeve is 90mm.

84mm B50 High Compression Piston

This again is the first barrel bored out to 84mm for the BSA B50 high compression piston. If the barrel is to be used with one of my oval squish band heads a flat crown piston must be used.

84mm B50 High Compression Piston

On this shot with the piston set a T.D.C. the height of the crown can clearly be seen and is a snug fit in a re-worked Norton cylinder head. The compression can be raised or lowered by the simple use of compression plates under the cylinder base.