Do check valve clearances!!! -Visual

If you take a look at the right side of the valve you can see the hairline crack. There are actually 2 others as well, but im not sure they are visible.

I decided to check compression before starting the detail and minor restoration of my 76 kz900. Compression was slightly below spec (120 psi on avg.) for 3 of 4 cylinders while #3 was only giving me 30 psi. I poured oil into the cylinder as the troubleshooting method would suggest. The pressure increased to 75 psi. This would typically mean that the issue is not the valves and is related to ring/bore size. Further dismantling the bike I found that all the cylinders and rings were slightly worn but still in good condition and not exceeding any wear limits. My assumption was that my gasket had gone bad (although no signs), or that the rings were bad. I kept hoping that perhaps the valve was the culprit, and indeed it was. This flaw in the valve would never have been found if I hadnt removed the valves and cleaned off carbon.

The moral of my little story is that relying on the oil test to determine cause of compression loss may not be an accurate method, additionally, valve clearance will not only cause poor performance and although that may seem to be common knowledge to most, I was unaware that neglecting could also lead to catastrophic failure internally. I was unable to fit my smallest feeler when checking clearances and on 4 of 8 valves I had to insert shims with a difference in shim number of 20 or clearance of .020, wow!

Nice Find ! You cant take too much for granted on these 30+ year old bikes. Good thing that they were built tough, I'm not thinking that today's FEA engineered, 15,000 RPM masterpieces are going to stand the test of time so well.

Ouch.
Leak down test would have showed the valve problem, but by the time there that bad, rings would be a very good idea. Hope you have a way to cut your seats, it wouldn't be a good Idea to lap new valves to those seats. Maybe a trip to a machine shop?

This valve is the only one that I believe to have been constantly stuck open. The rest looked great and the seat of this valve is not in bad shape either. New rings on the way. I am going to attempt to lap a new valve into this seat and give it shot. Thanks.