KZ440 LTD Compression Woes

Hello KZ Riders! I have just finished reassembling a 1983 KZ440 engine. I initially tested the compression in both cylinders and found it to be above service limit (107psi) but below the spec in the manual (156psi). I replaced the piston rings, base gasket, head gasket, and cleaned and lapped the valves. I am reading about 125 in the right cylinder and 90 in the left. When I added some oil to the left cylinder the compression shot up to about 135 psi. I know that would generally suggest the piston rings are not sealing well. However, I am at a loss. I am no expert but I followed the manual as well as I was able to. I am willing to tear it down again but I was looking for advice to make sure that I don't run in to the same issue the next time. As always, thank you guys for your help.

Measure the piston to cylinder wall clearance?

Adding oil to a cylinder to determine whether or not the rings are not sealing can be deceptive. See the link below for an explanation. Ed

www.kzrider.com/forum/2-engine/608083-wo...e-guide-seals#780709

Did you bottle brush hone the cylinders? How many miles on the engine since the rebuild. What break in procedure was used? Compression test with throttle held open? Valves properly adjusted?

Thanks for the replies. I did hone the cylinders but I used a three stone style cylinder hone. I have not ridden the bike more than a couple miles to warm it up and retest the compression with the throttle wide open. If there are break in procedures available that would be great. The only adjustment I made to the valves was to clean and lap them and install new valve stem seals.

I found this post from wiseco, blog.wiseco.com/proper-engine-break-in-after-a-rebuild , Seems to be comprehensive. Any thoughts or recommendations otherwise?

Put some miles on it.


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