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bore clearance query


Well Known and Active Forum Website User
Non-VOC Member
hey folks
what thoughts are out there on bore size/clearance for the diecast shadow pistons?
E7/7AS/D 7.3:1 Piston Diecast

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
There are a few different opinions around.On my original Comet I run .005" bottom skirt clearance, 35 deg. magneto advance and have had no problems and negligible oil consumption.My newest Comet nipped up an original Specialloid so I have gone to diecast with .006" clearance.There is a theory in Australia at the moment that premium fuel (98 octane) burns cooler and is less likely to cause seizures.The evidence so far is only anecdotal; any comments from the ethersphere? I add that my bores are round and the muffs fit properly and are true to the crankcase mouth faces.


Well Known and Active Forum Website User
VOC Member
Chankly's advice sounds good. With a twin you may choose the tight side of the tolerance, but with a Comet it seems best to choose the loose side. When pressing a Comet you have all that heat working one piston very hard.

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