I did a valve adjustment today for the first time. While turning the crank between each cylinder, I could hear a faint hissing come from inside the head.

the torque required to turn the head varied as we went through each 180° turn of the crank. We figured that was due to whichever cylinder had all the valve closed, as we were making compression.

This hissing occurred at some point during each 180° turn which makes me Think that I’m losing some compression on ALL CYLINDERS?!

Is this air leak sound normal when turning the crank?

 

This this is just the compression being passed though the valves, as they start to open. No problem.

 

Thanks Wind. We came up with a few wild theories as we went along!

 

If you have bad compression the engine will not run well.

 

If you remove the spark plugs the adjustment procedure is much easier, particularly with high compression motors. The noise is normal, without plugs there is no compression and no noise.

 

If your plugs are due, excellent time to change them. If not, excellent time to inspect them. They can tell a lot about engine health.

But no need to remove them for VA if you don't want to. If you have a long socket handle, its not difficult to crank the motor to next position.

Note that when doing a VA, precise timing marks accuracy isn't required. You are adjusting valve when its closed. When cam lobe points away from follower. Its closed for nearly 180 of the cams degrees. All that matters is the valve you are adjusting is cam up.