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So I got my cylinder block for my '77 KZ-1000 back yesterday from Millennium Technologies after boring and honing the cylinders. In order to eliminate the pitting in the cylinder walls they ended up going out to 71MM for each and then they surfaced the top of the block. Looks very well done in my estimation. I did not want to go to 72MM unless it was necessary to get rid of the pitting. Today I ordered a K1045 Wiseco piston kit for the bike. I was reading some of the information regarding setting piston ring end gap and I have a few questions for the experts.

End gap for the top ring on a 71MM (2.795") piston for street use looks like .014". This determination comes from the Wiseco formula chart showing bore diameter, (2.795") X .005"=.01397". The 2nd ring end gap, which should supposedly be larger, figures out to .01537" Do these figures/results sound about right? I might have thought the 2nd ring end gap should have been a bit larger, but what do I know? This means that the difference in end gap between the two is only .0014", or about a thou and a half.

Regarding the oil control ring, as I understand it there is NO end gap to worry about here, just that the ends must not overlap correct? And lastly, is there any end gap to worry about on the oil rails? Thanks for any help on this......
Rick H.

The Wiseco Piston ring instruction.

It is not good practice to bore and hone the cylinders without the pistons.
This maybe ok for your everyday car engines but not motorcycles.
To get the correct bore clearance the shop should have requested you supply the pistons at the same time and i'm surprised they did not refuse to do the block without..
You may (most likely unless you are very lucky ) end up with too tight or loose clearances because of this.
As for ring gaps - Follow the figures given by Wiseco.
Slightly larger second ring gap and oil ring should not be gapped and no overlap.

zed1015 wrote: It is not good practice to bore and hone the cylinders without the pistons.
This maybe ok for your everyday car engines but not motorcycles.
To get the correct bore clearance the shop should have requested you supply the pistons at the same time and i'm surprised they did not refuse to do the block without..
You may (most likely unless you are very lucky ) end up with too tight or loose clearances because of this.
As for ring gaps - Follow the figures given by Wiseco.
Slightly larger second ring gap and oil ring should not be gapped and no overlap.

I am of the same mind as ZED,
For correct fit each piston is checked for exact size and the cylinder is machined for exact clearance needed for the application ..
Slight variances in piston size are common .
Sorry , But this is the truth
Dave

Not to sound like a complete goof, I agree in a perfect world with non-pitted cylinder walls in the block, having the cylinders bored and honed to each specific piston would have been the best option. The problem was that we really didn't know how far oversize the bore was going to have to go to keep it in my 71MM request. I'll mic the pistons when I get them against the cylinders and see how I stand. Worst case is re-bore if they aren't in the ballpark. One of my main beefs is that piston manufacturers for these bikes don't like to supply pistons in smaller increments say 10 over, 20 over and so on. Kawasaki supplied them as such but not aftermarket. So the way things commonly go you have to jump up to 71MM from 70MM which is a pretty good jump, like almost .040". Rarely have I ever seen anyone jump that much at one time unless there were serious issues. Another issue was the pitting in the cylinders was not uniform in that there were deeper pits and not so deep pits which just compounded the decision making process. Looking back I suppose I could have just said lets go to 72MM and be done with it and ordered the pistons to go with the block, but there were no guarantees going to 72MM's was going to get all the pitting out. I'll just have to see how it all pans out.
Rick H.

Boring cylinders W/O Pistons is a NO-NO !

Yeah good machine shops won't bore and hone without having the pistons. If the shop bored without the pistons look for another machine shop.

Moving from Std to 71 mm means you went to first oversize, which is 0.5 mm. If that did the job in terms of eliminating the pitting then that's great...the block can be used for many thousands of miles before going to second oversize.

Okay to follow up a bit on my situation, I received the 71MM piston kit from Wiseco yesterday. Last night I did my own mic'ing of the pistons and cylinders and while I am not an expert at measuring things I like to think I am pretty good at it. The pistons were all almost dead on at the same measurement which surprised me. I expected a little fluctuation in diameter, but these are almost spot on to five decimal places. Where I fall down a bit is that I don't have a really good internal bore gauge as I have had no need for one. I do have an old Lufkin two point internal bore or cylinder gauge and I have a Starrett telescoping bore gauge that you insert in the cylinder then transfer it to a 3" mic for your measurement. After multiple measuring attempts to check and re-check and check again, I have no greater reading on cylinder to piston clearance then .00240". The manual I have calls for no greater reading than .0026". The minimum clearance I have in my cylinders is .00225" and the manual calls for no less than .0017". So at least at this point I feel relatively sure things are looking pretty good. I should state outright that I have always been a fan of bigger is better in most cases such as this. As a backup plan to verify my readings I am going to take the block and pistons to the place that did the boring and honing and they will check to make sure all is acceptable.

Two things I have already noticed with this Wiseco piston kit. One, the 2nd compression rings have an end gap that is beyond what they recommend on their spec sheet. On two of my ring sets the 2nd ring end gap is .0018" straight out of the box and per the spec sheet it should be .0016". Is this of any real concern, or should I just leave it be. The top or 1st ring is within spec. Also, Wiseco sent along a metal MLS head gasket. Would you recommend using this gasket or the one piece Cometic that I have already purchased? Thanks....
Rick H.