One Cylinder Compression 90 psi Other 3 120 - 130

I just ran a compression test and one cylinder is 90 psi the other 3 are 120 to 130 psi. I would like to know whether the 90 psi is acceptable to leave?
I have also checked the valve clearances intake are 0.06 and 3 at 0.08 mm (manual says 0.1 - 0.2) exhaust are 0.18. 0.18, 0.1, 0.08 (manual says 0..15 - 0.25). I am going to have to remove the camshaft to replace the shims with thinner ones. Should I use shims to try and get as close to the maximum clearance? Final question the manual says to use a valve lifter do I really need that tool or can I use something else?
I am rebuilding 1980 KZ550A that has 14,000 km, 8,800 mi. PO said it hadn't run in over 12 years and it didn't have a battery, carbs were off no fuel or vacuum lines. PO said there was problems with ignition thought it was the coil. I am a newbie to motorcycle mechanics and just started taking the bike apart to determine what needs to be replaced. I am getting to the point where I am just about beyond my capabilities.
Thanks Tomas

TomasDouglas wrote: . . . manual says to use a valve lifter do I really need that tool or can I use something else? . . . .

Suspect using the wrong manual, because the mentioned tool is for engines having visible shims.

Good Fortune!

Was the engine fully warmed up when you checked the compression, and did you have all the spark plugs out and the throttle fully open? Those things should be done when checking it or the readings will be misleading. In any case, since the bike hasn't run in so long it could just be a ring sticking, and that may cure itself when the bike runs some or you may want to put a little lube in the cylinder to help free it up. Someone else may be able to say which product would be best to use for that purpose. I wouldn't sweat it unless it was still low after I put a few hundred miles on the bike.

Regarding the valve clearances, those on my KZ650 were set in the middle of the range (I had to reset one when the bike was nearly new) and have never gone out of spec since 1977. Generally, the clearance don't change much on these bikes as long as you use a top tier fuel, so I would set the clearances near the middle of the range. I'm not sure what the manual means by a valve lifter - maybe a little plunger to pull the buckets? Any little plunger should do, but I wouldn't use a magnet because if it magnetizes the bucket you may eventually have metal filings stick to it and wear the cam. Do one cam at a time, don't pull them both together. Take lots of photos of the position of the cam sprocket timing marks before you pull them so you can easily reset them. Also, stuff a rag in the cam chain tunnel so you don't drop anything done into the abyss. Ed

Here's some other info that should be helpful before you start the project. Ed

kzrider.com/forum/10-new-members/589649-...r-savannah-ga#594587

No carbs on for compression test is the same as holding throttle open. If it did not have carbs on it and sat for a long time with nothing covering the intake holes, you could have a dirt dobber nest or something. I have the exact bike and just about the same scenario. I tore mine apart and found nothing. I took the head to a bike shop to have valves removed and he said what 650ed said. I should have ran it awhile and then re check compression. Once the top end is torn down, you might as well re ring it, lap the valves, and put on new valve seals. I found new rings from $35-$55 each and a gasket set is around $100. So my $200 1980 KZ550A has got expensive. I put it in my shed and started working on my 1000. Good Luck Here's my dilemma www.kzrider.com/forum/2-engine/592323-lo...sion-on-one-cylinder

It's common to have low compression after extended storage time. I'd swap out the shims and put the bike into service for 500 good hard miles and then test again. Dollars to donuts the compression will come up to normal levels.

Nessism wrote: It's common to have low compression after extended storage time. I'd swap out the shims and put the bike into service for 500 good hard miles and then test again. Dollars to donuts the compression will come up to normal levels.

That's right.

650ed Thanks for the response and advice. Since the bike didn't have carbs or exhaust on when I did the compression test I will go ahead and change the shims carefully, but leave the pistons and rings as is. I got a copy of the service manual from Lou D's web site, his information on the 550 is great.
I sure appreciate the help from experienced members.
Tomas

HAFROD Thanks for the reply I am going to leave the head on and just change the shims and carry on. I already have over $800 sunk into parts with a battery and tires still to be bought. Your post was very interesting but I don't think I have the skills for tearing down the engine like you do.
Thanks Tomas

TomasDouglas wrote: HAFROD Thanks for the reply I am going to leave the head on and just change the shims and carry on. I already have over $800 sunk into parts with a battery and tires still to be bought. Your post was very interesting but I don't think I have the skills for tearing down the engine like you do.
Thanks Tomas

I don't really have the skills either but the guys on here are willing to help when you get stuck. I'm just starting out too.