Here's how to make the piston stop device.
File, grind, or machine the rolled-over area of an old spark plug away so the porcelain can be punched out.
Then tap a 3/8-16 thread into the plug shell and insert a piece of 3/8" all thread long enough to touch the top of the piston when it's a few degrees away from TDC.
Use a jam nut to position the threaded rod for the best depth. If you're doing this on a stovebolt six, it's necessary to put a bend into the all thread to make it touch the piston because the angle of the plug thread and the cylinder don't play well together.
Yes, turn the engine by hand, or use a pry bar on the flywheel teeth to gently move the piston against the stop.
I've been using that method of finding TDC on race engines for over 40 years.
Jerry
