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Join Date: Jan 2011
Location: Smack in the middle of Illinois
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Measure the diameter of the cylinder in mm - 85mm (397cc) is standard, 85.25mm (399.5cc) is first over bore and 85.5mm (402cc) is second over bore - anything over 85.5 requires the installation of aftermarket pistons like Wiseco, Namura, Pro-X or the like. Wiseco is available in 86,87,88 and 89mm.
86mm bore makes it a 407cc, 87 = 416, 88 = 426 and 89 will make it a 435cc (commonly referred to as the 440 kit) To bore to 89mm the cylinder has to be sleeved with a special heavy wall sleeve or the original sleeve will break in use.
If the piston has been shaved, there are indications of milling and there will be no markings on top of the piston. Before a piston is shaved it has numbers and sometimes an arrow indicating the exhaust side of the piston either stamped or engraved into it. You will have to remove the carbon to see the markings (if any) by bead blasting, buffing, or heating (burning the carbon off) - I usually bead blast or buff. Also, if there's anything left of the rings, oversize rings will have a number stamped on the top side of the ring near the end where the two ends of the ring meet when installed in the cylinder.