I have a single cylinder engine with overhead cams. If I set the crankshaft/piston to Top Dead Center (TDC) with the cams set to the compression stroke, would it make a difference if I were to rotate the crankshaft 360 degrees to TDC (1 revolution) without moving the cams, or would I have to perform a 720 degree rotation (2 full revolutions) to set the crankshaft back to the "TDC on compression stroke" to be in sync with the cams?

Silly question, but I want to be sure. Thank you.

  • Welcome to Motor Vehicle Maintenance & Repair! Commented Aug 21, 2019 at 17:23

1 Answer 1


I assume that you are talking about a four-stroke cycle, so if you rotate 360 degrees then the engine will be at TDC changing from the exhaust to the inlet stroke which is not TDC for the combustion stroke.

If the cam is not connected and you are setting up the timing from scratch then TDC is TDC. Once the cams are in the correct position and connected by gears or chain to the crank then the TDC positions are either start of power stroke or changing from exhaust to inlet.

  • Yes, it is a four-stroke. Yes, the cam will not be connected after being set to the compression stroke/combustion event, as the timing chain will be replaced. So after disconnecting, TDC is TDC, no matter how many revs of the crank. Thank you.
    – John Smith
    Commented Aug 21, 2019 at 17:28

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