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The new piston sits exactly where the old one did, just above the deck. The head gasket provides the clearance so the piston doesn't hit the head. I'll do a comp test soon and let you know where it's at in comparison to factory.

The kit was sold to me as a direct bolt on, no machining required. I assumed it would bolt on after reading a few forum posts that said that it would bolt straight on with no worries and talking to the supplier who said the same thing. The bottom of the cylinder (the part that sticks out below...

So with the "jug" properly machined the engine went back together with no more issues and fired first go. Have rejetted the carb, seems to have some more power, I'll post again once she's run in properly.

Public service announcement! The GN250 big bore kit (out to 300cc) available on ebay does not fit. I got hold of the kit a week ago to discover that the skirt on the barrel is too large a diameter to fit the engine casing. After having the skirt machined down to fit I also discovered that the...