Sherco Top End Engine Rebuild Kit - 290cc - 2005 to 2010

Piston Sizes

The factory recommended piston to cylinder tolerance for the 290 is 0.027 to 0.037mm, 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.

These pistons usually come without the half moon shaped cutout on the bottom of the skirt on the inlet side, some Sherco's have the cut out some do not even straight from the factory, we find it makes no difference which piston you use.

18mm Gudgeon Pin by 52mm long
Centre of the gudgeon pin to the top edge of the piston 29.1mm
Overall height 68mm
Height from top to the edge of the piston 4.5mm
Weight including rings, gudgeon pin and C-clips 328 grams

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 1.20mm.