The term TDC refers to Top Dead Center and that is where the piston is at that point. You are right that it passes through there twice during the four cycles. The old flywheels had a UDC marking for Upper Dead Center.


1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed


My Chevy Master 4 Door is on the Road!