1985 tri-z 250 question

[Zakk]

got a new piston but have a questions. the old piston has ports on the side and the new one dont. are they needed? also the old piston fits more snug then the new one. it doesn't have any play but will go right through the cylinder no problem vs the old one you have to help it through. the old one measured 68.4??-68.6??? so we figured it was 68.5mm, which is what that new one is. (we did not hone or bore the cylinder as the shop said it was not needed.)

[YTZ drew]

That "port" above the piston pin hole in the stock piston is for balancing, the newer piston probably weighs less and doesn't need the hole. As far as the fit, the old piston looks like it has some scuffing, which is basically metal that has been displaced and built up in certain areas, making it fit tighter in the bore. With the old piston looking like that, are you sure you don't need to hone the cylinder?

[muthey]

put up pics of your cylinder for us also are you running the old piston with the rings on it as they are on in the pic you shared. I recommend a light hone no matter what the shop says as any little nicks or scuffs are going to instantly damage your new piston. I also recommend going to a machine shop and having them mic your cylinder and piston so you know actual sizes for them.

[ATC-Eric]

Yes, you need to measure your cylinder.