Hi does anybody know if the 250 90/91 cylinder / heads / pistons are interchangeable as have a 91 cylinder and head which has had work done on it (engraved on side) and assume it will be an upgrade even in standard form for a 90 bottom end?
I have already purchased a std size Wiseco Prolite piston as will be getting a fresh Nikosil coating on which ever cylinder I end up using and pretty sure that the piston said it fits 90/91 so am guessing it will be fine, I know you cant use a 90 piston and 91 head on the 125 hence the question. Thanks
Also does anybody know what the standard measurements of the cylinders etc are in case they have already been modded?
The Eric Gorr booklet says (means nothing to me but will get the shop to sort)
"CYLINDER MODS
The weakness of the I990 and 1991 cylinders is the timing of the exhaust and transfer ports. There isn't enough time for the exhaust gases to depressurise the cylinder before unburned mixture gases flow from the transfer ports.
Turn down 0.5 mm from the cylinder base, raise the exhaust port [0 26 mm from the top of the cylinder, and inStall a (046) head gasket from Kawasaki."
