Of course there is always the way that doesn’t require any parts – well; maybe a piece of wire, or something to use as a pointer near the teeth on the flywheel ring gear.

 

-Remove the rotor 1 spark plugs (and one from rotor 2 to relieve the compression).

-Turn the engine until the tip seal on rotor 1 is in the center of the leading plug hole.  Mark the gear tooth at the pointer.

-Turn the engine until the same tip seal is visible in the trailing plug hole. Mark the tooth at the pointer.

-Now turn the engine back to the gear tooth at the pointer that is half way between the 2 marked.  The tip seal is now at TDC.

-The center of the combustion chamber is 60^o on the rotor from the tip seal; or 120^o on the E-shaft.

- Count the total number of teeth on the ring gear, and divide by 3. Now rotate the engine by that number of teeth (either direction) and rotor 1 will be at TDC.

 

Al G

Last fall I assembled several versions of engines (rotor housings) to proof this method, and found that you end up with a TDC mark that is 4 to 9 degrees BEFORE actual TDC. The plugs have been moved about over the years, and the distance between plugs changed (probably for California). 

 

This method is fine for a fresh engine to just drop in the distributor or crank angle sensor to start the engine.

You would need a good TDC mark on the pulley and an adjustable timing light, or another mark at your full advance point.

 

You can do the hose in the plug hole idea, and just put your tongue over the end of the hose. Rock the engine gently over suspected TDC and feel for the null (no pressure/no vacuum) presto, TDC.

 

Take a plug out of number 2 housing to make this very easy (no compression).

 

Here is the rig to mark the pulleys with accurate TDC marks before assembly.

 

Lynn E. Hanover