Ariel OHC engine service data

[marwsk]

Hi. The frame in my Ariel is almost finished. I would like to start the engine overhaul in January. Do you have any service data for this model?
What is the recommended clearance for JP pistons? What should be the clearance between valve and valve guide?

Have any of you fitted a larger carburettor to an OHC engine? What do you guys think of the movement, the original looks like for a 50ccm motorbike.

[Roger Gwynn]

Hi Marcin, it is looking good. The clearance is .004" to .006", usually one would aim for the middle of the figures but better to go for the high figure for the rear cylinders. JP pistons have the same expansion rate as any other

[nevhunter]

Fours don't need large carburetters. Each cylinder is only 150cc. Nev

[paul.jameson]

If you ride the bike at anything above 55mph you will be astonished at how much fuel passes through that small carburettor. In my experience, the OHC Four is much the least economical Ariel model so I agree with Nev - you don't need a bigger carb (and I doubt you could fit a larger flange of one between the exhaust ports).

[marwsk]

More than 55 mph? It is safe?

[paul.jameson]

In answer to your question about fitting a larger carburettor, please find attached details of one fitted to a 1933 OHC Four. There were other modifications to the bike, the most important being the supercharger. It lapped Brooklands at over 110mph, so the 55mph I mentioned in an earlier post is indeed safe.

Apologies about the reproduction but my scanner is not good enough to capture the information from a photographic negative.