Uh Oh Low Compression

wireman wrote: Did anybody else notice the numbers jumped between 30-50 psi by dumping a little oil in the cylinders or is it just me again? :laugh:

Ever seen a motor, even a new one, that the numbers didn't increase when you add oil?

10% leakage is the commonly accepted number on a new broken in motor, and when you add oil you reduce the leakage to zero (or near enough). Take a newly rebuilt GPz750 that's just broken in and has 180 psi compression, add oil and it will be over 200.

If you have a motor in great condition, try it yourself. Do a dry compression test then a wet test.

Just saying there might be more to it than just a couple valves being out of adjustment since they all made a pretty decent jump by adding oil is all

ThatGPzGuy wrote:

bountyhunter wrote: zero valve clearance equals crappy compression.

Got it. I understand 2 and 3 need to be adjusted but I am not getting very good results with 1 and 4. I am afraid I'll go thru all the work of adjusting the valves just to have to tear into it again to do the rings.

I would think the valves will need to be adjusted anyhow, no matter what. So you won't actually be doing any extra work for yourself other then taking the tank off and valve cover. But its worth the extra information you will gain from doing another compression test and leak down test after the adjustment.

A leaking valve will allow compression to be lost (through the leaking valve) even after having added oil to the combustion chamber before the compression test.

The added oil helps prevent loss of compression past the pistons/rings into the crankcase.
But, the added oil generally doesn't help prevent loss of compression through a leaking valve.

Good Fortune!

Thanks everyone, I didn't really expect the wet test to tell me anything about the two cylinders where I know the valves are too tight. I was mostly concerned about what the compression results of #1 and #4 are telling me about the general condition of the engine. my reasoning is if I have to tear it down anyway I might as well do a complete valve job as well as the rings.
Although I've had this particular bike for the last 5 yrs and 4,000 miles I don't think it was well cared for before me. I also paid someone to adjust the valves about two thousand mile ago and I find it hard to believe they would go out of adjustment this quickly (if he did what he said he did).

I'll take the advice of those on the board and adjust the valves and see what that gets me.

Steell, what makes you think #4 has a stuck ring?

Ok I checked the valves.
It was a lot easier than I thought it would be. All of them were fine except #2 and #3 intake valves. The only one that worries me is #2 since it had no clearance and a 2.15 shim. The chart calles for a 2.00. What if that does not provide enough clearance? Time for a valve job?

You could always pull the shim out and stack a whole bunch of feeler gauges in there to find out which shim you need before ordering

I could but the smallest shim in the chart is the 2.00.I don't suppose I could run without a shim?
I would think not.

Here's info from the KZ1000 FSM about "tipping" a valve stem, which shortens the stem, whereby a thicker shim may be fitted.



Presumably, a similar procedure would apply to other models.

22,000 miles seems awfully low mileage to already be at the thinnest shim size.

Good Fortune!

ThatGPzGuy wrote: I could but the smallest shim in the chart is the 2.00.I don't suppose I could run without a shim?
I would think not.

No Im just saying to pull the shim out and see what you have for total clearance without the shim then subtract the clearance you need from that number,that will give you your required shim size.
That way you know if you can shim what you have,or if the head needs to be pulled off for more work.

22k miles is not a lot of miles, sheesh -- these KZ motors are bulletproof, they last tens of thousands of miles in the Police versions.

But if your valve clearances were wrong, as you said the clearances were too tight, maybe you have burned valve seats and the valves are not sealing and that's why you're losing *some* compression. But at 22k miles, no way are your valve seats burned to the point that you need a thinner shim than in the shim chart or you have zero compression. The compression in 1 and 4 is low. The zero compression in 2 and 3 is not reliable in my opinion.

However, if you had someone else adjust your valves previously, and it was *not* because you were too busy with work or something, here's what I'd do:

1) read the valve clearance checking procedure in the factory shop manual for your bike, not a Clymer or Haynes manuals, the *factory shop manual* for your year/model bike, and make 100% certain you understand how to check clearances correctly -- not 'I think I got it' degree of certainty, but "My favorite Grandma's life depends on me getting this valve clearance check right -- otherwise she'll die" I mean you are *certain* you are checking the clearances right.


2) now re-check the valve clearances.

I just really find it hard to believe you're at zero compression on #2 and #3 if as you say, you paid someone only 2000 miles ago to adjust the valves. Surely they would have told you that you were at the margin. Zero compression is catastrophic failure.
Having the valves stay open due to no valve clearance/shims too thick just 2000 miles after they were last adjusted, no. I just don't buy it.

If your valve seats are just burnt bad, I guess that's possible, but again not 2000 miles after a *correctly done* recent valve adjustment.

Unless the person who did the valve adjustment 2000 miles ago was high or something and got it wrong or was otherwise incompetent.


Also, buy a 2nd compression tester *just to be sure.* I have three different compression testers, they're not that expensive, that way if I catch myself saying 'the compression's fine, this gauge must be out of calibration' I grab another one to get a '2nd opinion.' I don't mess around with it sometimes, I take the carbs all the way off. I want a compression test. Especially if I have CV carbs, I yank 'em. I want a solid reading from the bores and the CV carbs have a butterfly valve, not a direct means to *guarantee* the throttle slide is opening for the compression test.


Something's fishy here. I just don't think a 22,000 mile KZ motor has hit the "Shim limit" in that chart. I just don't see how a valve seat can lose that much material after only 22k miles to put you limit-down out of the shims chart to the point where you need a thinner shim than is in the chart. Check your method of performing the valve clearance check. Maybe yank the carbs and re-check compression.

Thanks Everyone for your advice. It is much appreciated.
Here is where we are: I got a 2.00 shim from my local kawsaki dealer and was able to get the proper clearance on one of the valves however the other one requires a 2.05 which I did not order. I learned this by using Wireman's adice and measureing the gap with the smaller 2.00 shim. So,once i get all the the shims collected and installed I should be good to go. However the #3 intake will bear watching (it will have the thinnest shim). My next course of action is to check and double check the compression and perhpaps do another leak-down.

NewOld, Thanks for taking the time to reply. After checking the valve clearances a few times I am sure I got a pretty good handle on it. It is actually easier than I thought it would be. And yeah, the guy I paid to adjust the valves and sync the carbs was a bit of a flake. I don't think he is in business anymore.

I'll post my compression results after it is all back together (minus the carbs).

Thanks again,
JIm