I used the option 3 below, but what is not mentioned there is that is TDC for the tip seal.  TDC for the combustion chamber is 60 degree from there on the rotor; or 120 degree on the eccentric shaft.  Easy enough to figure degrees by counting teeth on the starter ring gear.

The trailing plug hole is on the top. The leading plug hole is on the bottom. With only slight variations from year to year for pollution and such, the plug holes are equidistant about the center of the housing.

 

Suppose now that we are looking into the number one housing from the front (in the car) of the engine.

Suppose that the apex seals are numbered: 1)  2)  3).

 

We turn the crank until number one apex seal is in the center of the trailing (top) plug hole. Put a paint dot or scrap of tape on a flywheel tooth under your pointer. Note that the number 2 apex seal (clockwise from number one) is now nearly at the bottom of the housing. You can do this a few times, while moving the pointer a bit one way then the other, so the pointer will be on TDC at the center of a valley, or the center of a tooth for a better look under the timing light.

 

Turn the crank backwards (anticlockwise) until the number 2 apex seal is in the center of the leading (bottom) plug hole. Again make a paint dot or place a scrap of tape the flywheel tooth (or valley between teeth) on the flywheel under your pointer.

 

Half way between those two dots or tape scraps is TDC within a degree or so, depending on the year of the housing. Mark the flywheel half way between the two dots. Turn the crank in the running direction (clockwise) until the pointer is over the half way point. The engine is at TDC front housing. This is the reference point for all timing.

 

Slip on the front cover and crank pulley without turning the crank, and look at the TDC mark on the pulley. Always sight along the same bolt head on the water pump or alternator mount, so all observations are based on same/same data.

 

The mark on the pulley will probably look to be dead on TDC. (in some cases, there will be no mark at all, and you can make one if you like) Compared to the flywheel, the pulley is rather small, and it is difficult to detect small changes in timing, or to accurately set the timing. So, mark the flywheel TDC tooth permanently with paint. Divide the tooth count by 360 and get the degrees per tooth for your flywheel. Choose your timing (say 26 degrees BTDC). Count the number of teeth forward (in the direction of rotation, clock wise) from the TDC mark, to get to 26 degrees, and mark that tooth or valley with a different color paint, like yellow so it will show up to the timing light. You can mark adjacent teeth so as to make changes for slightly more advance, or retard.

With the flywheel sitting in the 26 degree advanced position, mark full advance on the crank pulley under the stock front pointer. Now you can check timing while standing further from the prop.

 

NA rotaries are insensitive to small timing changes. So absolute accuracy is not required. If you think it is at 26 degrees and it is actually at 27 or 25 it is of little importance. Boosted engines are completely different animals, and timing under boost is a real big deal. Apex seals often damage the exhaust turbine on the way out.

 

Lynn E. Hanover