Hitchcocks Forum

Whilst stripping my engine I found it has a 2mm plate fitted to the crankcase. It had the higher comp acralite piston in it but I didn't think a plate was necessary for those pistons? The engine has clearly been apart before but how can I tell if the head or barrel has been skimmed? 2mm plus two gaskets must equate to around 2.5mm difference in piston height in the head? I don't know if the bottom end is standard but are there any measurements I can make of the rod whilst still connected to see what I have. The crank flywheels look very rough with dents in them (indian) and the rod is polished alloy but it's looks like an Indian rod with no small end bearing or bush? Do some bore and bush the little ends out of interest? Harvey

Who knows what goes on in someone`s head? It could be the work of some teenager learning by experience, it could have been done to fix a pinging problem, could be anything. If the bike ran appropriately before, leave it alone, or you might be opening an expensive can- of -worms If you don`t know what you are doing and money is not a problem, let a trained mechanic sort it out. If you are skilled at this sort of work, it will be an interesting project for you. Best of British luck.

Most Factory flywheels DO NOT have dents on the outer rims...


Measure your combustion chamber capacity with heavy oil and a Burette, keep the motor leaned over so that the plug thread is uppermost.


70cc capacity is approx 8.25 - 1


80cc = approx 7.25 - 1


90cc = approx 6.5 - 1


1cc of piston displacement is equal to approx 6.6cc




Running a High comp piston(?) with a 2.5mm of 'compression' plate is counter productive.


Bullet small ends are not bushed from new; no need.

Bit of a way off measuring the space in the chamber yet but some handy advice thanks. Head and barrel to be machined over the next week then for the bottom end!