Peter Grey wrote:

I found an accurate and perhaps easier tool to make is simply a solid rod in
a spark plug. By bring the piston gently up against the plug rod in both
directions, making a mark for each on the flywheel or balancer, and then
splitting the difference, you can find TDC easily.

This took maybe 10 or 15 minutes to make and it sure is nice to watch
that dial gauge as you rock the crank back and forth. It even gives you
a feel for just how much slop (not much) there is in the basic method.

Ted