We have done this a little different.

Turn the crank one way until the piston just stops moving up the cylinder and mark the crank.

Turn the crank the other way until the piston just stops moving up the cylinder and mark the crank.

Measure the distance between the two lines, divide by two and mark the crank.

You now have top dead center.

You can put most anything in the spark plug hole and watch it rise so you can mark the crank.

This works very well and takes no special tools .