Say you want to verify tdc on an assembled engine, maybe suspect the wrong timing tab / balancer combo or slipped inertia ring.
A few days ago, i decided to slip a 6" pc of solder straight into my sbc's #1 plug hole (all the way in to the opposite cyl wall, with the "tail" held in my hand) to measure my assembled squish/quench. While rotating the engine back and forth thru tdc by hand with a bar, i noticed that it was very easy to locate tdc using the squished solder as a "feeler gauge" to locate the piston's highest point. I did this blind a few times just to see how accurate it was, it was repeatable to about 1/2 degree. It also aligned with my adjustable pointer that was carefully adjusted with a degree wheel during assy.
It's pretty easy to feel the "dead band" area (where there is no piston movement near the top of the stroke) using the squished solder as a feeler gauge. Much like adjusting valves, moving the squished solder in/out allows you to feel when the moving piston "grabs" the solder, while rotating the crank back and forth across tdc with a bar using the other hand. TDC was in the middle of the dead band. I'm not saying this is the most accurate method to find TDC, but i was amazed at how accurate it was.
Solder comes in many thicknesses, so start out with something thin like .062, as jamming solder in that's a lot thicker than the clearance might cause piston damage. Flux core solder is what i used, very easy to squish.
