well true TDC can be found by taking a old spark plug and making a piston stop.
by removing the porcelain insulator and running a tap thru the center of the spark plug body.
screw a bolt thru the plug body so there is about 1" sticking thru the engine end of the spark plug body.
round the end of the bolt nice and round and smooth on a grinder.
install the plug in to # 1 cylinder with the piston down in the cylinder.
install a pointer on a timing gear cover bolt that sticks over the front pully.
if there is no pointer there to start with.
you can make a pointer out of a piece of stiff wire or welding rod.
remove all the other plugs so the engine can be turned easy.
be very careful and slowly turn the crank by hand or with a wrench untill the top of #1 piston contacts the spark plug piston stop bolt end.
now mark the front pully right under the pointer
be very careful and rotate the crank the other direction until the piston makes contact with the piston stop again.
mark the pully again now split the difference between the 1st mark and the 2nd mark and mark the pully and you have true top dead center and a zero refrence if you are using a degree wheel
don't ram the piston aginst the piston stop or you will punch a hole in or damage the top of the piston.
remove your custom made piston stop plug and throw it in your tool box and it should work on any engine that has a 14 mm plug
cool huh learned that one in 1956 reading hotrod mag and still have the first one i made and have used it a gazillion times
