kawasaki Z250A top ring dont fit

[justanotheryo...]

Hi got new rings in 2016. Finally sit down to put them in and theyre 1.47mm thick. Top ring groove is 1.40mm and it aint getting any wider. Ive cleaned off all baked on carbon.
Part numbers are correct. Service manual says gap should be 1.50mm.
I have 2 Z250`s 1980/1982 both have the same pistons.
None have a 1.50mm gap.
Any help would be greatly appreciated

[stinkwheel]

Either the manual is wrong, the rings are wrong or the piston is wrong.

It sounds like the rings and manual agree with one another so the piston is currently outvoted 2:1 against.

Could the piston crown have collapsed? Why does it need new rings? What happened to the old ones? Are they the correct pistons?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jeffyjeff]

Check to make sure that all of your parts are original equipment (OE) Kawasaki. At first thought, it sounds like you might have aftermarket pistons in your bike, but the fact that your 1980 and 1982 bikes both have the same pistons make that improbable.

Manufacturers make design improvements over the production life of the motorcycle. You may have received piston rings for a model made later in the production run. I say this only because your title states Z250A, and generally the alpha designator advances as different generations go into production. If that is the case, you could A) try to source rings that fit the 1.40mm ring grooves on the pistons you have, B) look for aftermarket parts as a set, or C) purchase OE pistons that fit the thicker rings you purchased in 2016.
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History shows again and again how nature points out the folly of men - BOC

[MCN]

Oversize Rings in error?
Check with supplier.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Robby]

Worth measuring the ring end gap on the old ones to find out if they actually need changing. If they do, you can either try to buy another set of rings and hope they fit, or buy a couple of piston kits.

Of course, if the rings are worn out then there is a fair chance that the bore has worn a bit oval as well, and it could be worth going up a size on pistons and having the barrels bored out.

Very quickly you're in the realm of throwing money at a bike that isn't worth it. When you get it all back together and working it will feel exactly the same as before all the work.

[justanotheryo...]

Thanks for all the quality advice. It had to be something logical and it turns out kawasaki made a piston change after a certain engine number. With a thinner top ring.
No mention of it in the manual...or the appendix for the A2.
My old pistons top gap is past the limit and rings
everything else is close to the service limit.
I might just put the old ones on a lathe and bring the gap out to 1.50mm. Put the new rings in it.

Do you reckon thatll work.

New pistons $100ea

[Pete.]