top end rebuild....again. whats reusable?

swest wrote: I don't see any cross hatch. Did you measure the clearances of the pistons or the valve guides?
Steve

I'll stand corrected but there appears to be a huge gap between the bore and the piston or is it a reflection.

You can clearly see the rings. That's why I suggest sizing the pistons. Can put a ring in them and measure the gaps. If too wide the compression could be good but it will leak oil and have a lot of piston slap. I'd also expect an out of round condition.
Steve

swest wrote: You can clearly see the rings. That's why I suggest sizing the pistons. Can put a ring in them and measure the gaps. If too wide the compression could be good but it will leak oil and have a lot of piston slap. I'd also expect an out of round condition.
Steve

Steve, agree from what I can see there is too much ring showing its as though the bore is too big but then it could just be the way the photo looks. Resize the piston to the bore and the ring gap.

Need better pics.
Steve

As previously stated the main rings in a larger bore will hold compression because they spring out a fair bit but the oil rings don't spring out much. Personally I hope I'm wrong about the bore.

It is not unusual at all to find pistons made with the area above very top land a smaller diameter then the rest of the piston.
Still, I'd slide the cylinders off and have the bore and pistons checked for proper clearences.
Otherwise, no matter what you think, the valve guides are shot or the bonnets are not snapped down over the guide grooves.

missionkz wrote: It is not unusual at all to find pistons made with the area above very top land a smaller diameter then the rest of the piston.
Still, I'd slide the cylinders off and have the bore and pistons checked for proper clearences.
Otherwise, no matter what you think, the valve guides are shot or the bonnets are not snapped down over the guide grooves.

Agree, I did say that the pictures aren't that clear for me, you are right pistons have a taper but the gap looks big on photos. Valve guide slop would be easy to check with the head off. Lets hope its not major.

Stuff I'm thinking about this one....

1. Your cylinder bores look way to shiny for new rings to seat / break in properly. A few passes with a flex hone to prep the bores will work wonders with oil consumption - BUT - If the cylinder has never been bored / honed, I would have it checked to see if the bores are actually round and straight, too. '81 and up KZ and GPz's went through a period where Kawasaki wasn't getting the cylinders round from new. I would have it checked and corrected if it is suspect in any way (yes, that means new oversize pistons).

2. Even if part 1. above checks out, the pictures do look like there is too much piston to cylinder clearance - the top piston ring land is seldom more than 5-10 thou smaller than the largest diameter of the skirt, below the oil ring groove and 90 deg. from the wrist pin bore, generally - you should be measuring the clearance anyway as per part 1..

3. The piston top that is clean - looks like mucho oil pumping - while two of the others have an excessive amount of carbon build up. In the cylinder head - check your valve guides for wear first, then if ok, install new valve guide seals after reading up on how to prevent damaging them while they are being installed. Lots of home mechanics end up damaging new valve guide seals because they are unaware of proper installation procedures (which includes how to check valve stems for sharp edges and install the valves without nicking / cutting the new seals).

Happy Wrenching!

One more that just occurred to me - the ring grooves should be thoroughly cleaned before installing new rings on used pistons.

How clean? Spotless, if you want guaranteed results!

I soda blast them with a micro tip on my pressure soda blaster so I just clean the grooves without affecting the lands. A piece of old piston ring with the end squared with a file can be used as a scraper - works great, but takes longer. Cleaning the oil control groove can be done the same way, along with using dental picks gently to remove dirt (but not aluminum!).