The piston diameter on my 198B is 73.75 giving a size of 256cc.  The underside of the piston is stamped DINAMIN, and although the piston and bore are in good condition I wonder if anybody knows if this was a fairly standard mod just to maximise the capacity rather than being overbored so many times over the years for some strange reason.  Also does anybody know what bike would this piston? might have come from? GasGas perhaps?? The InMotion site shows piston sizes up to 73.00 only.  Thanks.

You'll never know the answer to how many rebores but the Dinamin pistons were common aftermarket pistons available for many makes of bike in the 70s to 90s, later called GPM, no longer available now. They were available in bigger sizes than the current aftermarket pistons for Bultacos

Edited May 15, 20224 yr by woody