Yes. You need a positive-stop spark plug adapter, easy to make:
1. make sure the piston is close to bottom dead center. Screw the modified spark plug in. Turn the bolt in pretty far to make sure it protrudes deep inside the combustion chamber. Now turn the crank over slowly by hand (all other plugs removed to reduce resistance).
2. when the piston hits the tip of the bolt, stop turning immediately and make a mark on the crank pulley where the TDC indicator is. this is not your TDC yet, just the first reference mark
3. turn the crank the opposite direction, it will make almost a full turn until the piston once again touches your plug bolt. Make another reference mark on the pulley at TDC indicator.
4. Your true TDC is exactly half way between your reference marks, so measure the distance between them and divide by 2, and make your TDC mark. If the distance between reference marks is really big, you can turn the plug bolt OUT a little and repeat the whole procedure, the piston will then move higher up in the cylinder before it stops against the plug bolt, and then your two reference marks will be closer together.
I used a jam nut on the bolt because you want the bolt-to-plug relation to stay 100% rigid, no wobbling. I threaded the inside of the spark plug after I knocked the porceline out. Cant remember sizes off the top of my head.
Jan
