The only thing you need to worry about with the piston not at TDC would be the tendency for it to be pushed to the bottom of the stroke when you apply the air pressure. If the piston is halfway thru the stroke, it's going to have the most leverage to turn the crank. If it doesn't move, then I don't suppose it would really be an issue.
As far as photo #3, I have trouble understanding why there's a yellow range on gauge #2. Less leakage is better, but it can't possibly be zero unless the piston is glued into the cylinder (maybe by rust), but I think you'd know that.
[on edit] Jerry's right about the rings being looser at or near TDC. I hadn't thought about cylinder taper.
Last edited by klhansen; 11/20/2024 2:14 AM.
