Compression issues

Hello again. 1981 kz1000 csr. I had the bike running good. Then it started running rough again. I pulled the number one plug and installed gage. I could only get 90 psi while turning it over. Dumped a little oil in the cylinder and got about 140 psi. I am assuming the rings are shot. Can I do this repair with the engine in the frame? Should I do a full rebuild? Any advice would be greatly appreciated. 

Did you remove all plugs and hold the throttle wide open when checking compression? If not, warm the engine up good and check compression again, before tearing the engine down.

The answer to your first question is yes, you can do cylinder repairs without pulling the engine from the frame.  Whether you should do a full rebuild depends on a lot of factors, including your financial situation, your expertise and other issues, if any with the bike.  It's a personal choice, but if it were me I would probably pull the engine and do a complete inspection, replace any worn parts including the timing chain and put it back to together.

I think the best way to go for me is to replace the pistons and rings. Now the question is do I go with stock size or bore it out a little? What is the process? I have read about sleeves. What is the safe way to go? Again, thank you for all the help.

A leak down test will tell you the truth about your missing compression.

If you have a service manual it will have tolerances on pistons, cylinders, valves etc.  My guess is that your pistons may be OK but you may need to replace rings and hone the cylinders before rebuilding the engine.  If the cylinders are worn beyond tolerance you can bore them slightly to what is called first oversize.  In that case you will need new pistons and rings to match.

 

There is not enough information to make an informed decision regarding the plan of action.  For example, as mentioned already, was the engine warm and the throttle held open when performing the compression test?  Have you kept up with valve adjustments on the engine, and are all the clearances currently in spec?  How many miles on the engine?  What specifically is the bike doing when you say it's running rough?  Is it firing on all cylinders?  Did you check spark on all cylinders?  Does the engine burn oil?  Foul plugs?  Is the gas tank free from rust and debris?  How long since the carbs were rebuilt?  

Where can I find the procedure for the leak down test?

The engine was warm and the throttle held wide open. The compression on the #1 cylinder was very low. Then as per the Clymer manual, I poured some oil in the cylinder and the compression came up to 130 psi.

I apologize 140 psi.

The leak down test show you, (you can listen and hear), where the compression pressure escape on TDC.
It could be escape over the piston rings (engine vent, oil fill cap).
It could be escape over the IN or EX valve port site due to carbon build up on the valve seat and head seat ring surface.
Dump the Clymer manual into the bin please!
 

jpacewic wrote:

Where can I find the procedure for the leak down test?