I'm on a 1968 Enfield Bullet (350cc), although my questions are probably fairly generic. So far I have come from India to Turkey, but the bike seems to have had enough now! On arrival here, it became apparent that it required a re-bore, but luckily I was carrying an over-sized piston and rings as spares.

The re-bore has now been done, but it still seems rather tight. To begin with, the piston was seizing every 5km (when the engine gets hot). After repeatedly waiting for it to cool down, and then continuing again, I have over the course of a few hours brought this distance up to about 20km. Since my experience of this is non-existent, and my mechanical knowledge barely any larger, my first question is: should I expect seizing initially after a re-bore? If so, how rapidly should the new piston wear in?

If, as I suspect, the cylinder needs to be bored out a bit more, how tight should the piston rings be when everything is cold? At the moment, the ends of the rings close tightly, presumably reflecting the fact that the piston only just fits inside the cylinder. Should there in fact be a small gap between the ends of the piston rings, to allow room for expansion of the piston? Actually, I've just found some specifications in the manual, where it says that the gap when new should be 0.015-0.020 inches, so perhaps I've just answered my own question. There's not much room for error, though, since the maximum permissible gap is 0.030 inches!

Any advice much appreciated, since I'll have to consider abandoning the bike if I can't fix it!

James