I know you already figured it out Astro, and nice post Jim.. but for any of you who are like me and can't read formulas and can only add, subtract and divide by 2:
What you'll need:
* Degree wheel
* Pointer (wire / coat hanger)
* Piston stopper
* Something to mark the cae and flywheel with (Sharpie / tiny paint brush / file etc.)
1 - Put the degree wheel on your crank / flywheel.
2 - Set up a pointer (piece of wire or coat hanger) on a flywheel cover screw.
3 - Put a piston stopper in the sparkplug hole.
4 - Roate the crank CLOCKWISE until the crown of the piston hits the stopper and it stops.
5 - Set the degree wheel to 0 (with the pointer) (Be careful not to move the degree wheel independantly of the flywheel when you're rotating the flywheel)
6 - Rotate the crank / flywheel COUNTER CLOCKWISE until it stops.
7 - Write this number down (we'll call this "number 1")
8 - Subtract "number 1"from 360 (the result will be "number 2")
9) Divide "number 2" by 2 (the result will be "number 3")
10 - Add "number 3" to "number 1" (the result will be "number 4")
11 - Remove the piston stopper.
12 - Continue to rotate the crank past where you stopped COUNTER CLOCKWISE until your degree wheel reads "number 4" at the pointer you've made out of a wire)
13 - Mark your flywheel and case here.. this is TDC..
Done!... It's that easy!
To get to say 18 degrees BTDC for example, rotate the flywheel COUNTER CLOCKWISE 18 degrees from your new TDC mark... Mark the flyweel.. this number will be to the RIGHT of your TDC mark on the flywheel.