Leak Down-Bad Rings

Hello, '82 KZ1000J Roughly 25,000 miles,  I'm having Issues that looks like may be piston related,  IF I end up finding out the rings are bad (leak down etc.) .  Is it possible to just replace the rings? In a car I would expect to bore the cylinder and get new pistons. But I see discussions on just re-ringing. What is the normal thing to do? I realize if the cylinder is scored I would have to bore.  Best place to get rings?
Thanks,
Ken In Orlando

The need for a re-bore and pistons would be determined by condition and measurements taken once stripped. Mileage seems low to need this level of work - Why do you think you have a problem ?

I agree with Wookie.  A thorough and proper inspection will indicate what work needs to be done.  Personally, if cylinder bores are in spec I would not change rings unless one or more were broken.

You seem to be anticipating the work you need to do before doing an inspection.  There are several checks you can do without dismantling your engine.  Have you checked your compression?  That would be my first step.  Follow the manual recommendation for the procedure.

I have found that if you take the top end apart to measure the bores you should always freshen up the cross hatch and use new rings if the bores are within factory spec.

If you try to reuse old rings on a fresh hone job its a big crap shoot, then never seem to seal properly and at worst can blow oil.

This has happened to me on more than one occasion, its better to invest a bit more $$ to do it right. There is nothing worse than tearing apart a top end only to be disappointed and have to redo it all over again!

I wouldn't even consider re-using the original rings!! A compression test is a pretty feeble test if it's already blowing smoke, pretty much worthless considering unless there's mechanical failure somewhere. Why you might ask?? If you've got a shabby 3-piece oil ring set oil is already slathered the clearance so it'll give you a false reading because its a temporary hydraulic sealing not a proper mechanical one. More telling is a leak-down test!! 

Compression test may show good compression.  That would make me suspect valve seals if the engine is smoking.

As far as ring sets go Kawasaki part # 13008-5035 is Standard Bore replacement. Provided You still have that 998CC original cylinder block used between 1981 thru 1983. They call it a 69.5mm bore but i believe that's just a easy size to say, actual measurement is fractionally smaller. Has been a while since i did a true J and we bored it out to 70mm anyway. If after measuring taper, checking deck for flatness, liners for cracks/gouges and deem it serviceable without further machining. You can always use a set of NPR 69.5mm ring sets. They are drop-in exact replacements for stock pistons. All 4 sets can be had for around 100bucks. But of course you'll be checking those pistons too and everything else. Sounds like Fun!! 

asphalt900 wrote:

I wouldn't even consider re-using the original rings!!  More telling is a leak-down test!! 

Agree with asphalt900!!  A leak-down is pretty much the gold standard in evaluating how well your combustion chambers are sealed.  Along with the gauge reading on the tester (street motor <10%, race motor <2%) you'll have the following - Bad intake valve - you'll hear air rushing out of carb mouth.   Bad exhaust valve - you'll hear the air coming out of the exhaust system.  And, bad rings, you'll hear it through your crankcase breather.  Pretty straightforward..

And, also agree on not reusing the original rings.  If bores are still round and within spec, then hone and use a fresh set of rings.  Keep in mind, also, that your bore diameter will probably increase by about 0.0005" after honing.

Good luck with your project!
 
Mike

A bore gauge is needed to check the cylinder condition.  Measure out of round and taper at top, middle, and bottom of the piston stroke, then again at 90 degrees to your first measurements.  Kawasaki allows .002" but I don't like to see more than .001".  Regarding rings, I've always used new, but I know guys that have reused rings if the end gap is good, and they achieved acceptable results. Considering those NPR rings are only $100, it's a no-brainer, though.

Lot's of good advice but as per my first post - why do you think you have a problem ? what are the symptoms ?

At this Point just researching all the options.
I have been chasing an issue for over a year. Bike nor running smooth. Some headers reading 300, 350 degrees others 120. I have checked valve clearance, rebuilt carbs. New plugs, wires, coils, rubber boots. Rebuilt carbs again and put in new throttle seals. Always sync with a mercury stick. Compression test shows: Dry #1 142, #2 127, #3 140, #4 135. With a squirt of oil #1 155, #2 136, #3 153, #4 150.
I am thinking of buying a leak down tester and was asking questions to determine what I may do to fix any issues.
Sounds like if I need to I can Ball hone and use new stock rings IF the cylinders are ok.
My plans when it cools down are to 1. pull carbs and compression test again, 2. check valve clearance again, 3. perform leak down and go from there.
 

Leak test is definitely the way to go (it tells you so much without any dis-assembly) #2 seems to improve significantly less than the other three on the wet test so possibly a valve not seating (the leak teat will identify this) - the compressions are within 10% (best to worst) so I don't think that would be responsible for a 200 degree difference in exhaust temp !!!! - how do the plugs look ?