KZ440 Oversized Pistons

I'm working at figuring out the best way to rebuild after an oil leak and a piston seize last summer. I was able to free the pistons again using a lot of penetrating oil time, patience and working the wrench. The engine runs great at low rpm's and speeds, but get it up over 4k RPM or about 35 miles per hour and there's no power at all. It's like it's running off of a single cylinder.

I was going to bore it out for the next oversized piston, but it appears to have been overbored in the past, and the ".50" on it doesn't match up with the ".20" or ".40" stock oversized piston that I would have expected.

Does anyone know if there is a chart anywhere that I can refer to that would give me the piston sizes and cylinder sizes so that I could take a Micrometer and find out if I can rebore the cylinders that I have, or if I'm going to need to get one of these sets off of E-Bay and hope they haven't been overbored too much as well?

kz400.com has all the info you could possibly need, including manuals online.

.50 means .50mm, which is .020" oversize.

I think loudfastugly (Google for a link) might have oversize pistons.

Found it in my bookmarks

www.loudfastugly.com/

stallardj wrote:

I'm working at figuring out the best way to rebuild after an oil leak and a piston seize last summer. I was able to free the pistons again using a lot of penetrating oil time, patience and working the wrench. The engine runs great at low rpm's and speeds, but get it up over 4k RPM or about 35 miles per hour and there's no power at all. It's like it's running off of a single cylinder.

I was going to bore it out for the next oversized piston, but it appears to have been overbored in the past, and the ".50" on it doesn't match up with the ".20" or ".40" stock oversized piston that I would have expected.

Does anyone know if there is a chart anywhere that I can refer to that would give me the piston sizes and cylinder sizes so that I could take a Micrometer and find out if I can rebore the cylinders that I have, or if I'm going to need to get one of these sets off of E-Bay and hope they haven't been overbored too much as well?

Look at the tops of the old pistons. If they are oversized, they will have "+0.25" or some similar number stamped on the top. The standarad over sizes available go up to "+1.0" in increments of 0.25. As said, those are mm so it is 0.010" - 0.040" oversized range.

As long as you are not already at +1.0, you can bore to the next size.