I am checking timing on my 12-valve. I used a dial indicator on top of the #1 piston through the injector hole. Very accurate.

For timing purposes where does Cummins establish TDC?

Is it the instant the piston reaches it's highest travel?

If you mark the balancer at the exact point the dial indicator stops moving up, then rotate the engine further to the exact point it starts moving down and make a second mark, you will have two marks at the same exact height. TDC.

Is TDC the middle of these two marks? Is it the first mark? Is it the second mark?

And here is why I ask: depending on what you consider TDC my engine is either at stock 14 degrees or it's at 16 degrees.

So, I have very accurate marks on my damper for TDC but I don't know where Cummins defines TDC. Of course, they tell you to use the plastic pin. So I guess to them anywhere from 12 to 16 degrees is close enough.

I can get a lot closer than that if I know which TDC is TDC, know what I mean?

 

I mark in the middle of the two marks.

 

You are marking where the piston begins to dwell, and ends its dwell. The point inbetween is true TDC.