While this is sometimes a "close enough" measurement, due to piston dwell it's not an accurate method of finding TDC.When i tested mine to see if it was accurate I:
- pulled all he plugs to make the roation easy by hand
- then plugged the piston 1 with my thumb as I rotated the crank
- Puff out on the compression stroke blows ur finger out (a towel or kleenex works fine too)
- stick a screwdriver in the plug hole and watch it go up until you can see the piston top
- stop and pull out screwdriver before end of travel (mine got pinched, so i learned this lesson)
- and watch piston (shine light down plug hole) until hits tdc (stops moving)
- Mark on pulley at TDC mark
...but make sure it's on the compression stroke (rotor pointing #1) so that you are not 180 out.When in doubt, go to the horse's mouth. Remove the balancer center bolt. The keyway slot is always perfectly centered on the top at TDC.
Procedure for finding and marking TDC:
(0) Disconnect battery (don't want an accidental engine start)
(1) Remove piston #1 spark plug
(2) On piston1 make sure you're on the compression stroke by placing a finger in the spark plug hole to feel for outward pressure (you can also use a vac/pressure gauge with scharder valve removed on spark plug #1 hole to do the same thing).
(3) Put a piston stop into spark plug #1 hole.
(4) Rotate crank by hand clockwise until stop and mark temporarily on balancer
(5) Rotate crank by hand counterclockwise until stop and mark position temporarily on balancer
(6) Using a tape measure, mark halfway point between the markings above (#4 and #5) permanently on balancer as TDC
(7) Remove piston stop before trying to start car ;-)
Note: This method handles the "dwell" issue in finding TDC