KZ650 rebuild

So I started my kz650 this morning and it only ran on 3 cyl. Turns out that cylinder 2 was not firing... In the end I found the issue: I got 25psi on the compression test! So I check the valves.... still in spec... check the timing... still spot on. adding oil to the cyl raised it to 50psi.

So then I pulled the motor and took off the head. No bent valves and the valve mating surfaces were not 25psi bad. I lapped them anyways (woooo new shims....). Then I go look at the jugs to find the pistons sitting 1/8in below the surface when the advancer is set to the T mark.... I am using a 550 ignition system so maybe thats why its off? Perhaps the timing is off a tooth as well.... buuuuut it ran fine a day ago and just a week ago i had 100+psi across all cylinders. I set it to TDC and look at the advancer: F mark is actually TDC according to the pistons...?

I don't know whats up with that whole situation but the pistons and jugs were ok besides some slight side skirt wear and matching wear on the cylinder walls. Bores are still smooth though and I cant feel any imperfections. I did notice that there is no cross hatching visible. All the bores were right at 62.00mm (measured with mitutoyo digital caliper).


I think i just need new rings and a hone? Thoughts?
Pics: pistons and bores

Pistons and bores looking good.
If the piston TDC is on the "F" mark, ( ignition firring ), your cam chain timing is one link off !!!

Yeahp. that'd do it. Im guessing a valve mustve been out of sync and got a bunch of crap on the seat. Maybe slightly bent? But the mating surfaces looked pretty even on the valves.


Anyways! should I just re use the rings? They are like $40 per piston on ebay so ehhhh kinda expensive for this project.


EDIT: found some new rings for a better price, so ill get those and hone the cylinders