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How to Find Your Engine's Top Dead Center (TDC)

from wikiHow - The How to Manual That You Can Edit
If you have a car with no timing marks on the crank pulley, here is a really neat, accurate and cheap way of finding the engine's TDC. This is done with the engine in the car and the head torqued down.


  1. Make an indicator from some clear plastic tubing, a jar of light oil, and an old sparkplug.
  2. Break up an old sparkplug and attach a length of clear plastic tubing to it (make it airtight).
  3. Remove all the spark plugs.
  4. Stick your thumb in the #1 cylinder spark plug hole. Rotate the engine (see note below on tricks for this) until you feel pressure on your thumb. That's the compression stroke. TDC is at the top of this stroke.
  5. Screw in the sparkplug with plastic tubing attached and insert the other end of the tube into a jar of light oil. Continue rotating the engine. Bubbles will appear until the piston reaches the top of its travel. When it starts down on the next stroke, the bubbles will stop and oil will begin traveling up the tube. Stop at a convenient point and mark the tube. Then mark the crank pulley and the engine body at a convenient spot.
  6. Rotate the engine backwards and watch the oil recede into the jar. Continue rotating. As the piston continues past tdc and downward it will again suck oil into the tube. Rotate the engine till the oil again reaches the mark. STOP! Mark the crankshaft pulley where it lines up with the mark you made previously on the engine. You should now have two marks on the crankshaft pulley. The midpoint of these two marks lined up with the mark on the engine is tdc. Whoa! Almost like finding South with a wristwatch. Boy and girl scouts listen up.



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