Yeah Frank. But you have to be carefull to keep from braking the piston. I have done this to many of them without breaking one, but there is always a first time. The best way is to remove the cyl. and piston and place the assembly on an anvil or hard steel surface with the piston at the bottom of the cyl. Then take a large like 1/4" punch and place it on top of the piston dome and hit it gently with a light hammer. It will spread the top of the piston and restore compression. If it gets to tight you will have to lap it in again before running. The secret is to just tap it a few times and check to see how tight it is. When you get to the place that it drags pretty hard at the top of the cyl. it is good enough. Keep it rich for a while till it gets broken in again and it will last a long time.
Hi Jim,
I was given an old lightning bolt McCoy 29 with weak compression. Of course I had to try your method of tightening the piston. Tapped it a few times........nothing. Tapped it a few more times, voila tighter.
Ok, so now I tried to run it for a couple hours, resting between flipping and popping. It would start to go then stop abruptly. Prime it and start all over again.
New plug, same thing. While adjusting the NV, I noticed it was rather loose. I put in another NV (from another engine, ST type) and got it to run for almost a minute. But, it acted like the piston started to bind/heat up and stopped.
I'm going to try it again today and if I fail to get it working it'll go in the junk drawer with the rest of the antiques....... (read that as junk)