Thanks for the link and input.
Finally got to working on this. Pulled the engine out Sunday afternoon. Only a handful of bolts and it's right out on the bench. Had to do a bit of cleaning though. Still covered in Georgia clay from the last outing.
Pulled the valve cover off - nothing unusual at all. Valve clearances all look good. Valves look to open and close properly. Looking in thru the intake and exhaust ports doesn't show anything unusual at all. No obviously bent valve or anything. Hmm....
So, off comes the head. These pushrod motors are a lot easier than OHC motors in that regard.
Unfortunately, no smoking gun there, either. No evident 'ding' in the top of the piston, nor anything unusual looking at the valves in the combustion chamber.
So, to check the valve seats, with the valves closed under spring force, I pour acetone in the ports and look for leaks into the combustion chamber. Good sealing valves should not show any seepage for minutes on end.
For the exhaust, all looked good. Dry for 3 ~ 4 minutes until I dumped the acetone out. For the intake, not so good. Drips appeared immediately, even though to the naked eye all looked good. I only had to watch for 30 seconds. I think I've got my smoking gun as to why I could only develop 30psi compression.
Actually, thinking about it, 30psi is a weird value - one would usually expect good compression or zero compression, not something in between. What I don't know is WHY the valve stopped sealing. A bent valve (my original guess) would give zero, not 30psi. And the valve doesn't look burned although I haven't inspected it out of the head yet.
So, that's where I am now. Next steps will be to see if I can lap the intake valve and get good seating that way, or else I'll have to buy a new intake valve. I probably should just buy the new valve anyway and lap it once it gets here. Haven't even tried to source one yet.
I checked the pushrods and they DO have just the tiniest bit of bow to them. I rolled them across a sheet of mirror glass I have, and you can just barely see a tiny bit of bow. I don't imagine that it's significant though.
So, thoughts or comments?
