TDC
Piston stop. setup degree wheel and pointer. Install P.S .turn engine until the piston hits the stop, record number of degrees. Turn engine other way until the piston hits the stop. record number. Add numbers, divide by 2. With the piston against the stop, fudge the degree wheel until the magic number is under the pointer. To validate your math turn the engine the other way until it hits the stop. The degrees should be the same. Of course one will be BTDC and the other will be ATDC
Example 15 deg BTDC and 35 deg ATDC added = 50 degrees, divide by 2 = 25 degrees. Set the degree wheel so that the pointer reads 25 degrees BTDC & ATDC when the piston is against the stop.
Using a piston stop is more accurate than a dial indicator simply because it will load the bearings and remove ALL the slack from them.
On a simple single its super easy to use. . On a multi cylinder with heads and accessories on its a major PIA as combat pilot explained
A dowel can shift, get a long reach spark plug and make a piston stop.
WORD OF WARNING [img]{akamaiimageforum}/image/s11.gif[/img] IF YOU FINALLGET IT RIGHT, DONT tell anybody in your club. If you brag about being able to time an engine you will endup timing everybody's engine anytime it burps. Make every body think its Rocket Science, even though its so simple after a few times.