How to tell if a rotary is at true TDC?
 

This is probably a pretty dumb question, but anyways...... How do you tell when a rotary is at true TDC? With a piston engine you can just look to see when both intake and exhaust valves are closed and you know you're at TDC. Obviously though, there are no valves in a rotary, so how can you tell?

I dont think its called TDC on a rotor, I dont know much but there is two markings on the front of the bottom pulley, also just above it is a neddle sticking out of the block, line the first one up, I think the motor turns clockwise when looking straight at the pulley.
Hope that helps

If you are trying to set the timing on the Crank Angle Sensor (CAS), align the marks that he was talking about, then you have to align the marks on the CAS, then install the CAS where it goes without spinning its gear because that will change the alignment. A Haynes Manual will show you how to do this.

I thought somehow that when a piston engine timing chain or belt slips, something similar could happen to a rotary where what you're reading for the timing marks is actually off a few degrees of where it should really be. Like you may think you're reading certain number of degrees for the timing, but since the belt or chain slipped, the timing is actually off by a few degrees, so that's why you would look at the valves on the #1 cylinder on a piston engine to see when they are both closed so you're for sure it's at TDC and that you can fix the off timing.

Rotary engines don't have timing belts or chains because there is no cam shaft. There are no valves to be opened like in a piston engines. There are ports, and the rotor closes off the port as it moves past it. Go to www.howstuffworks.com and do a search for rotary engines. It will show you what happens inside the engine. Its got a cool video.

I already know MOST of the in's and out's (not all) of the rotary, and I've seen the thing on howstuffworks.com. I guess the way I wrote my question made it sound as if I didn't. I just wasn't sure if there was any way that the timing could get messed up AS IF it were a piston engine and a timing chain or belt slipped. That's why I asked if there was any way to tell if a rotary was at true TDC. From what you guys have told me, I guess there isn't any way for the timing to "slip" from TDC on a rotary.

Answer
 

About 6 years ago, I wrote up the answer that you're looking and Steve Cirian archived it on his website website. Do a Google search.

The short answer is yes there is a TDC on a rotary. It happens when (if I recall correctly) the rear rotor is at the minimum displacement (i.e rotor face is centered between the two sparkplug holes).

Yeah, that makes sense. Thanks for the info.