QUOTE(VaccaRabite @ Oct 2 2020, 03:21 PM)
QUOTE(rgalla9146 @ Oct 2 2020, 11:04 AM)
The most accurate method to determine true TDC is to thread a stop into the #1
spark plug hole. Rotate the crank (slowly, by hand) until the piston contacts the stop.
Mark that spot. Now rotate the crank in the opposite direction until the piston
makes contact again. Mark that spot.
True TDC is the mid- point between those marks.
The ignition rotor is a little better than an approximation.
While this would work, its overly complicated.
Just go to top of travel and take a visual inspection of the valves to make sure they are closed for that cylinder. That is TDC for that cylinder. Bonus points for marking this in paint in the timing notch in the doghouse, but not even that is required since you don't need to do this very often.
Zach
It is certainly not an everyday necessity, it is the most accurate way to determine
true TDC. If your fan or flywheel are not marked ( and even if they are ) this will provide an accurate location.
A stop can be a modified spark plug as described that has a probe
that can be threaded in or out to provide a stop in piston stroke.
Summit or Pegasus would probably offer some version.