Low compression on one cylinder

Hello,
I just did a compression check on my 1980 KZ1000 Shaft. Numbers 1, 2, and 3 were 135-140, but number 4 was 115 dry. Wet it came up to 140. As I understand it this indicates worn or damaged rings.

The odometer shows 8,600 miles. I bought it last summer as a fix-up/clean-up project. It ran when I got it, but not very well. I cleaned the carbs, replaced coils, did a "Wired George", and now it runs great. It was not stored well by previous owners; some rusty bolts, faded paint and decals, but overall not too bad. Transmission is smooth as silk.

Here's my question... is it unheard of for a KZ with only 8600 miles to have worn rings in one jug? Is it possible that the bike actually has 108,600 miles on it? I know these are good engines, but has anybody run one that far? I would think there would be more problems than this one has.

Thanks,
Phil

Might want to perform a leak down test for it may be a valve issue.....

Pull the plug and compare to the others... If rings are the problem for that cylinder, this plug should be oil fouled....

Ride it till every part of it will burn you, then do a compression test WOT and go with those numbers. I've had bikes with compression all over the place after a few minutes of running, only to all pull up to 150 after afew hot blasts!
Also, dont do any tuning till she's burnin' hot as well!

If everything runs great, I wouldnt be too concerned, unless your a perfectionist with her :laugh:

id say check valve clearances to see if that cylinder is hanging open a little,could be part of the problem

When I got my bike the highest compression I got was 135 psi from 1 cylinder. Two more were around the 100-110 range, and the last cylinder was 75 psi! I rode it all summer and fall like that. Always started on the first kick, it just smoked a bit :laugh: but she ran fine! That was with 78K miles + on her.

That plug does look kind of gunked up (see pictures...one on the right is from one of the 135 psi jugs). Didn't notice until Old Man Rock mentioned it.

I'm not real worried about it since the bike does run well. I'm just curious about the cause, and hoping I didn't buy a bike with 100,000 more miles on it than I thought.

How far can these beasts go, anyway?

MadPhil wrote:

...just did a compression check on my 1980 KZ1000 Shaft. Numbers 1, 2, and 3 were 135-140, but number 4 was 115 dry. Wet it came up to 140. As I understand it this indicates worn or damaged rings.
The odometer shows 8,600 miles. I bought it last summer as a fix-up/clean-up project. It ran when I got it, but not very well. I cleaned the carbs, replaced coils, did a "Wired George", and now it runs great. It was not stored well by previous owners; some rusty bolts, faded paint and decals, but overall not too bad. Transmission is smooth as silk.
Here's my question... is it unheard of for a KZ with only 8600 miles to have worn rings in one jug? Is it possible that the bike actually has 108,600 miles on it? I know these are good engines, but has anybody run one that far? I would think there would be more problems than this one has....

Imo should quit worrying about the compression figures, put at least 1000 miles on her, and then do another compression test.

"Standard" is 128~156 psi with 100 psi service limit.
Spec is less than 14 psi between lowest and 2nd lowest, so 115~135 isn't much out of spec anyhow.

The above figures are "ideal," and many of the large fours perform quite well with only 100 psi and more psi differential among cylinders.

If not already done, change the oil and filer, and RIDE.

Good Fortune!

After a good ride of at least 20 miles to attain full engine operating temperature, allow to cool overnight, and with engine cold, torque the head.

Good Fortune!

Phil, Just a thought, but a 30 year old bike w/ just 8K miles has "set". Chances are your' low cyl has 1 or more rings "stuck" in piston lands. sometimes simple use/heat cycles will free them...more agressive (cheep) approches if this is the case are, steam cleaning,adding a couple tablespoons of Rislone or ATF thru plug hole & letting set for a day or so, or running a Rislone or ATF mix w/ engine oil for @ 100 miles prior to an oil& filter change.The note pertaining to checking valve clearance also has merit, not just for tight, but loose as well.after prolinged setting carbon deposits often come loose & can lodge on valve faces. I seriously doubt your bike has turned 100k, as other wear would be obvious, IE; worn out peg rubbers, wheel bearings, fork tubes, drive line wear et;all.luck G

As said, the FSM specs for compression are for a hot engine. If you have decent compression hot and it runs OK, ride it.

Leakdown test can pretty much pinpoint the problem racetoolz.com/

As to whether it has 100K+ miles on it.. very doubtful. While the odd one will make it there, it would have to be extremely well maintained w/regular valve adjustments, oil changes, etc. Most bikes profit from a top end rebuild around 60,000 miles. The state of your bike is not unusual and should run all day long like it is