Sherco Top End Engine Rebuild Kit - 250cc - 1999 to 2005

Piston Sizes

The factory recommended piston to cylinder tolerance for the 250 is 0.024 to 0.035mm, if you are considering putting the next size up piston in please be aware that your original piston will have worn down and any wear in the cylinder is unlikely to be uniform down the bore so please check the bore size all the way down the cylinder and from left to right as well as front to back, the factory measure the piston and cylinders at 24 degrees C. The piston is measured front to back and 19mm up from the bottom of the skirt, be aware that the pistons are manufacture tapered (larger at the bottom) and oval (larger front to back) to allow for unequal expansion of the piston in use.

The base gaskets are available in different thicknesses to allow the correct squish clearance to be achieved. The standard gasket is 0.5mm thick and is commonly used with one of the thinner shim gasket, some bikes even come from the factory with 3 gaskets.

We recommend you set your squish (the gap between the top edge of the piston and the cylinder head) to around 1.10mm.