What rings fit?

Does anyone know if newer 750 kaws rings will fit in my 1980 KZ 750 LTD pistons? I want to put new rings in but they are not cheap. I thought it was the valves but I just got them back from the machine shop and still no change in my compression(at 60 lbs in all four across).And I did check all the shims for the cams they are now all in specs by the book. (And what a big different that makes!)Thoughts?

Are you holding your throttle wide open when checking compression?

Good question eaglemhf and it got me thinking since I also have a 1980 750/4.

I did a quick check on the web and can see that the 2003 ZR7 which has a very similar engine has the same bore and stroke at 66.0 x 54.0 mm.

May be worth a closer look. On the other hand it may also be a long shot. Dont jump to any sudden decisions just yet as someone with cross reference software may drop by.

I would guess that the newer rings won't fit even with the same bore size. The piston lans will be a different depth and height in all likelihood. The newer engine is water cooled so will have closer piston to bore spec than an air cooled engine and the rings will be engineered differently. Are rings available for the 750? What do they cost? Before investing in an expensive set of rings, I would consider buying some tee bore gauges and measuring the bores (service manual tells you how) and measuring your current pistons (service manual explains how) to determine the piston to bore clearance. It may be that new rings won't seal if the clearance is too great. If that is the case, two options... 1. find good used cylinder / pistons and swap yours out. 2. buy an oversize piston kit and bore the cylinder.

Also confirm how the compression reading was done. Since you did the headwork without knowing that it actually needed to be done to raise compression, the possibility that the testing wasn't done right exists. To test, buy a press fit tester and remove your plugs and test one cylinder, then each of the others in turn. Hold the throttle open, as has already been mentioned. Last, add a teaspoon of engine oil to the 1st cylinder and test, repeating for the others. Don't pour oil into all of them at the same time or you will get drenched with oil (I know this to be a fact hehe). Hold that throttle open! If the compession bumps quite a bit, then the rings are not sealing.

The ZR-7 is an air cooled 738cc 4 cylinder model. A very nice bike. I took a look at one a couple of years back and was tempted.

I did check a bit further and you are correct WG - the rings and pistons seem to be different part numbers from the older KZs so I would guess no substitute.

Sorry if I sent you on a wild goose chase eaglemhf



Post edited by: JR, at: 2006/09/13 09:17

So ah yea I did all the compression test. Which I used a screw in tester. But I didn't hold the throttle wide open...mmm I wonder what happens when I try that tonight...:huh:

So I held the bike at WOT and the psi is still at 60 around the board...the bike might have to wait for about a year, I leave for a little trip for the Army. So I will figure this out in about a year. I just wish I could ride her one more time before I go...dang!

Just to clarify... when performing a compression test hold throttle wide open and do only one plug at a time, or take them all out?

Take all the plugs out,and check one at a time with WOT.

nfswift wrote:

Just to clarify... when performing a compression test hold throttle wide open and do only one plug at a time, or take them all out?

I took all the pugs out at once and checked them one at a time with WOT. I put the beast away for now...got to go play in the sand box for about a year. So next year when I get back I will put in new rings in. Thanks again for alll the help.

nfswift wrote:

Just to clarify... when performing a compression test hold throttle wide open and do only one plug at a time, or take them all out?

I took all the pugs out at once and checked them one at a time with WOT. I put the beast away for now...got to go play in the sand box for about a year. So next year when I get back I will put in new rings in. Thanks again for alll the help.

stay safe!