low compression KZ 550

Hello, I have a question for the engine gods,

I have an '80 550 LTD that i bought as a 2nd bike/project a few years back and So I finally got it all put back together last fall and started riding it. It never ran that good and recently started really bogging out. I did a compression test with a new teseter and got 115, 85, 95, 115. So I followed the repair manual and put a tbsp of oil in each cylinder and did another check, I got 150 - 200 so that means the rings are bad right?
I then proceeded to dis-assemble the engine, clean everything up and mic the cylinders, pistons, and rings according to the manual, so far I can't find anything out of spec, cylinders are .003" under the book spec and the rings and pistons are not even half way on the wear limits.
Pistons and rings were very carboned up and a couple of the rings seemed stuck before I removed them.
So here is my question, if everything measures good do i just hone the cylinders and re-install everything or should i replace the rings anyway? the pistons have a lot of pitting to the top but meausre good. I am not sure how to proceed, I would rather not waste money on parts that don't need fixed, especially on an old bike, but I don't want to go to all this work and still have low compression.

TIA, shane

since you took the time to take it apart, put it back together with new parts and hone the cyls, also I would take the head down,replace the valve seals and at the very least lap the valves in.

fix it once right, that way your not spending money a second time

If you think the piston rings are stuck, I believe Yamaha sell a product called "Ring Free" also Marvel Mystery oil is said to help.

ok guys,
I decided to not mess around, ordered new pistons and rings and gasket kit, in the process of pulling the valves apart and lapping the valves. Parts won't be here for a week or so so in the mean time im going to continue mic'ing everything trying to find anything out of spec. I will let you know how it ends up after the rebuild.
thanks, shane

If you need some new valve shims to reset your valve clearances, K&L makes a great starter kit available from most of the bike web sites, I bought 1 for my 550 and 1 for my 1000. If you lap very much the face on the valve and the seat will be to wide/ out of spec. Re-cutting the seats with the proper angles and refacing the valves if they can stay in spec would be a good investment, or buy some new valves, most likely the exhaust will be very pitted.

I honed the cylinders, installed new pistons and rings, installed the head and re-timed the cams. I got a set of feeler guages that went down to .001" and measured all the valve clearances, I have 0 clearance on all intake valves and I have 0 on two exhaust valves and .005 on one and .002" on one. So I am guessing this is a problem, It's as if the previous owner put in the wrong shims.
Book says .004-.008 for intake and .006-.010 for exhaust, so do i need to order new shims, can i just grind the ones i have on a precision grinder at work? does this matter if my compression is good anyway?

you don't want to grind them they are surface hardened. You MUST get the clearances in spec. If too tight, or you will burn the valve seats and ruin the head.

supergenius74 wrote:

...new shims...does this matter if my compression is good anyway?

bountyhunter wrote:

...MUST get the clearances in spec. If too tight, or you will burn the valve seats and ruin the head.

Clearance to spec (when cold) is required to assure clearance at normal operating temp after allowing for heat expansion.

This is the reason a compression test alone is insufficient. With barely any clearance, the psi may be okay when cold but lost when clearance disappears at normal operating temp.

Good Fortune!