Seems like the spark plug hole doesn't have enough angle to hit the piston. Ideas?
Put a 45 degree bend in the all-thread, insert it into the cylinder, screw the plug shell over it, and then lock the probe in with a jam nut against the plug shell with the bend pointing down. That should allow you to intersect the piston. Any other method of finding true TDC isn't going to be accurate, as there's a few degrees of "dead zone" with the piston at the top. I've used the positive stop method of finding TDC for 40-something years when checking race cams.
Jerry
