cylinder pressure

I have an '88 KZ1000P with 160 miles on it. Since it's winter, I decided to check the bike. I measured the cylinder pressure and it came out
1 - 170psi
2 - 137psi
3 - 135psi
4 - 165psi
Should I repair it before disassembling and measuring? Where can I find parts?

When were the valve clearances last checked ?
160mls ??
How regularly is it run ?
I would suggest check the valve lash, drop some WD40 in the bores and let it soak (remember to spin it over with the plugs out to clear the WD before starting) start the motor and run up to temp then check again (make sure you have the throttle wide open when testing) I wouldn't suggest "diving in" until you have a better idea of whether or not you need to

Sorry, 160,000 miles.
Valve clearances checked and OK.
Checked with the throttle open.
After pouring a small amount of engine oil into the cylinders, the reading is 190-200 psi on each cylinder.

GrzegorzSadoch wrote:

Sorry, 160,000 miles.
Valve clearances checked and OK.
Checked with the throttle open.
After pouring a small amount of engine oil into the cylinders, the reading is 190-200 psi on each cylinder.

That does then suggest worn bores (not surprising at that mileage)  I guess the next step would be to pull the cylinders and measure "how much" wear there is before deciding on a strategy. These readings seem high for a stock motor, due you trust the gauge ?

So I'm going to have to disassemble and measure the cylinders and pistons.

I wouldn't touch that engine.  135 psi will run fine.  Put a few hundred miles on the bike, then check valves and compression again.  It may bump up, but even if it doesn't, that's not low enough to warrant a teardown.

I concur with Nessism, don't tear that down and just run it. Try something like marvel mystery oil or similar (WD40) in cylinder #2 and 3 and ride the piss out of it.

Tear downs, even just top end deals are so expensive these days, you need to think twice about it. 

I would suggest a test with several different compression testers, and then if you not happy a leak down test is in order.

You can't dispute a leak down test, and the equipment may be on par with gaskets/rings/seals etc. or even less. Even if it comes back with bad news, the upside is you will still have the leak down kit.

A friend of mine has a KZ900 bored to 1015 and it ran on 130 PSI for a bunch of years before he did a tear down and bought new pistons. I rode that bike on 130 PSI and it was totally OK, it would not pull your arms out of the sockets but you could get a major speeding ticket on it

,, and then if you not happy a leak down test is in order" 
what is this test about?
Unfortunately, Marvel Mystery Oil is hard to come by in my country, but I have WD40. Should I add it to the fuel, oil, or cylinders? And how much?

GrzegorzSadoch wrote:

,, and then if you not happy a leak down test is in order" 
what is this test about? - If you aren't familiar with this process it's probably worth "googling" cylinder leakage test for an explanation of the process
Unfortunately, Marvel Mystery Oil is hard to come by in my country, but I have WD40. Should I add it to the fuel, oil, or cylinders? And how much? Remove the plugs and spray a generous amount of WD40 into the cylinders, let it sit overnight then before you re-fit the plugs spin the motor on the starter to blow out any excess residue of WD40. Re-fit the plugs and run the engine to burn off any WD40 left behind.

I agree with what the guys are saying about 135psi being plenty for the motor to run just fine, a leakage test is by far the best way to establish if there is an issue. However if the motor is stock then I would expect somewhere between 150 -160PSI on a good motor. The fact that you are getting 190-200psi on a 160k mile motor would suggest that your gauge is wildly inaccurate. If that is the case those 135psi readings are likely to be much lower ?

It showed 190-200 after pouring oil into the piston chamber (the oil sealed it) that's why such results

What does this test involve?

GrzegorzSadoch wrote:

It showed 190-200 after pouring oil into the piston chamber (the oil sealed it) that's why such results

What does this test involve?

See page one of the below thread for an explanation

low compression... another rabbit hole - KZRider Forum - KZRider, KZ, Z1 & Z Motorcycle Enthusiast's Forum

If one looks for 'problems', it's almost assured they will be found.  True of most any contraption.

Are you satisfied with the way the thing works (in this case, way the bike runs)?

If yes, do nothing.  Don't fix it if it's not broke/perfect.  Enjoy.

If no, tinker to one's hearts content within reason.  Take your time; do it right the first time.  Don't fall into the, "Why is there never enough time to do it right, but always enough time to do it over?" trap.

Good Ridin'
slmjim & Z1BEBE