How to Find TDC on a Number One Cylinder

by David Brown

Finding top dead center, or TDC, on the number one cylinder is a relatively straightforward task. On a four-cycle engine, each piston reaches TDC twice in a combustion cycle--once at the end of the compression stroke, and once at the end of the exhaust stroke. We can find TDC easily enough by simply aligning the TDC mark (the 0 degree mark) on the crankshaft damper with the timing pointer; however, this doesn't tell us if the engine is on the compression stroke or the exhaust stroke. Usually we're concerned with finding TDC at the end of the compression stroke. The process of finding TDC at the end of the compression stroke is called "dead timing" the engine.

Remove the coil wire to prevent the engine from starting.

Remove the number one spark plug. The number one plug varies; consult a shop manual for your engine to identify the number one cylinder.

Attach the remote starter switch to the positive terminal on the battery and the switch terminal (the smaller terminal) on the car's starter.

Hold your thumb over the spark plug hole, crank the engine using the remote starter switch. You'll feel pressure build up as the piston nears TDC. When the pressure reaches its peak, the piston is at TDC. Release the remote starter switch.

Align the TDC mark on the crankshaft damper with the timing pointer, using the wrench and crankshaft socket.

Tips

  • check You can use a helper in place of a remote starter switch. Have the helper operate the ignition key, and simply tell your helper when to crank the engine and when to stop.
  • check On cars with a separate starter solenoid, attach the remote starter switch to the starter terminal on the solenoid and the battery terminal on the solenoid.

Warnings

  • close Use extreme caution near moving parts.
  • close Don't forget to remove the coil wire or otherwise disable the engine's ignition system when using this method.

Items you will need

About the Author

David Brown began his writing career while still in college, writing and editing research grants and scientific papers. His work has appeared in such journals as "The Journal of Clinical Investigation" and "Gastroenterology." He currently owns a construction company in Boulder, Colo.

Photo Credits

  • photo_camera spark image by Zbigniew Nowak from Fotolia.com