1979 KZ1000 cylinder PSI

Well, remember that thread i put on here about a month ago saying i was gonna get a KZ1000 but im only 14? Well, i got some bad new i guess from my mechanic about the bike. He says that it has weak cylinders... Heres the message..

"Cylinders 1&4 have 135 psi 2&3 are at 120."

Is this ok, or does it need a rebuild or something... I just sold this other bike to make the money to buy this, iv'e been waiting for ever and have been looking forward to this bike for a long long time now.. Can i buy this and have it run ok for a long time?

Thanks guys,
KT

The valves should all be gapped correctly first, before a compression test is done.

Then, with an old air cooled bike, the compression should be tested HOT, like after a good 30min run.

I can almost guarantee that the compression would be much better, and likely much closer (within 10% numbers).

Those would be your baseline numbers.
Of course this guy wants to rebuild the engine, so he can make a $bundle$ off you, for a fairly easily performed job.

Do yourself a favor and get the bike back. Then BUY A MANUAL and start saving for some basic tools.

Good luck man!

PS. My buddy rode a 900 with barely 110 compression on all 4, for like 3 years.

As long as the compression is within 15-20% it should be ok. Just put some fuel and some fire in the hole and let her rip. Good luck with it.

Kitten Tooth wrote:

Well, remember that thread i put on here about a month ago saying i was gonna get a KZ1000 but im only 14? Well, i got some bad new i guess from my mechanic about the bike. He says that it has weak cylinders... Heres the message..

"Cylinders 1&4 have 135 psi 2&3 are at 120."

Is this ok, or does it need a rebuild or something... I just sold this other bike to make the money to buy this, iv'e been waiting for ever and have been looking forward to this bike for a long long time now.. Can i buy this and have it run ok for a long time?

Thanks guys,
KT

The service limit of compresssion on a 750 twin is 115 PSI (hot) not sure about the KZ1000, I thought they ran about 20 - 30 psi higher than the 750 twins. 120 - 135 might be servicable for a while on a KZ1000 (?).

If valve gaps are OK and the compression is low, you either need a valve job or new rings (or both). First check the valve gaps and make sure clearance is good. If you can squirt some oil in the cylinders and the compression goes up significantly, that means the leak path is rings. If it doesn't go up, it's valves.

what should the compression be on cylinders 1-4? I just wanna know how far off it is. I'll do the oil test. I didn't give the bike to somebody to work on, this guy is a mechanic and he wants to sell it to me. He don't seem shady at all in selling it. He told me the truth at least instead of selling me a shitbox. How do i check the valve gaps? Do i just remove the valve cover to do it? Or do i have to pull the whole frickin motor apart? Thanks guys

Hi KT, per the Clymer manual for 73-81 kz900-1000 "normal compression should be 130-160 psi, but readings as low as 100 psi is usually sufficient for the engine to start.."
I have a '78 1000 that had compression #'s from 70 to 130 when I bought it. She smoked a bit and used a little oil, but it always started up on the first kick and never missed a beat (till I dropped a tool down the cam chain tunnel ) I bet you'll be fine with 120-135 psi till you're ready to freshen her up!

I'll do the tests... thank you for the info on the PSI. I don't have a clymer for that bike. I have one for an 81 KZ1000 but not a 79. Will my bike most likely use oil and smoke with number that low? I just got a motor rebuilt for a different bike because i didn't know how to do it myself and my wallet is empty at the moment:/

Thanks guys

If the bike has been sitting for a while the numbers could be low just from sitting.

I installed a motor last year and one cylinder had bad compression. I went to the bike shop and got some ringfree and mixed it with the next two tanks of gas and the pressure in the bad cylinder came up.

Roy

Unfortunately I don't have a '79 OEM manual but here's the procedure and spec for my '76 KZ900 compressions...

Standard is 121 ft pounds.

Service limit is 85 ft pounds or a difference of 14 ft lbs between any 2 cylinders.

Based on the numbers you posted and in a non warmed up fully operational engine, you may be ok for the time being.

A leak down test would also inform you of some possible issues such as worn out rings & valve seating leakage...

OMR

Kitten Tooth wrote:

Well, remember that thread i put on here about a month ago saying i was gonna get a KZ1000 but im only 14? Well, i got some bad new i guess from my mechanic about the bike. He says that it has weak cylinders... Heres the message..

"Cylinders 1&4 have 135 psi 2&3 are at 120."

Is this ok, or does it need a rebuild or something... I just sold this other bike to make the money to buy this, iv'e been waiting for ever and have been looking forward to this bike for a long long time now.. Can i buy this and have it run ok for a long time?

Thanks guys,
KT

Sure wouldn't bet the farm on that mechanic's opinion. :pinch:

But can instead bet comp psi's are okay based on KHI's official FSM for 1979 KZ1000, namely:

Comp specs @ 128~156psi with service limit of 100psi and <14psi difference between cyls.

Some large four engines continue serviceable performance with even less than 100psi.

Imo, am concurring with others who suggested best to first assure valve clearances being to specs, and put some miles on your engine, before getting too excited about the measured cold comp figures, and difs between cyls.

Remember to change both oil and filter.

Good Fortune!

Will the compression most likely get worse do you guys think? The motor doesn't smoke or anything. I'm sorry or seeming like such a noob, but how do you do a leakdown test? Oh and thanks for all the info so far..

I think the advice here is to ride the bike or run the bike with a fan blowing on it and let the rings have a chance to warm and expand.

Leak down test can be found with the search function. Roy