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Hi Group,Just received my crank shims for my GT and am going to have cylinders bored to suit a set of 81mm pistons. Any of my britbikes I would aim for the .001 per inch of piston.Seeking confirmation or advice from the experienced.Bomber

Forged or cast? Depending on intended use .002"-.003" is the ballpark figure.The piston mfg. should have a recommendation.

Thanks for replying wdietz.Forged V2 pistons that were puchased by a previous owner.Bomber

I just did a couple engines and learned a bit. The clearance reguired depends on the alloy used. JE uses a high silicoln alloy that reduces the thermal expansion of the piston. They recomend .0025 to .003
On the other engine I used some 15 year old Aria pistons. I contacted them directly for guidance and was told to use .005 to .006.
There is no answer that covers all pistons. I would try to contact the manufacturer or the seller for specific specs. Hopre this helps.

Wow, .005-.006, thats a pretty fair clearance. Did you run that engine with that clearance?? Was it noisey??
I run Omega high comp pistons in a GTS of mine and they specified .0015-.003" I went with the .003" just because it can get hot in the summer time where I live.

Thanks guys,Recently snagged a Haynes manual.Gives clearance as min. .0008-- max. .0016 with a wear limit at .0055.These specs are for forged pistons.I suppose how diligent you want to be breaking in the new pistons can be a factor also.
Bomber