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

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. Image titled Find Your Engine's Top Dead Center (TDC) Step 1
    Make an indicator from some clear plastic tubing, a jar of light oil, and an old spark plug.
  2. Image titled Find Your Engine's Top Dead Center (TDC) Step 2
    Break up an old spark plug and attach a length of clear plastic tubing to it (make it airtight).
  3. Image titled Find Your Engine's Top Dead Center (TDC) Step 3
    Remove all the spark plugs.
  4. Image titled Find Your Engine's Top Dead Center (TDC) Step 4
    Stick your thumb OVER 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. Image titled Find Your Engine's Top Dead Center (TDC) Step 5
    Screw in the spark plug 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.
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    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.
  7. Image titled Find Your Engine's Top Dead Center (TDC) Step 6
    Open the bonnet and support it. Find a socket spanner and togglebar to fit the crankshaft pulley nut. Remove all of the spark plugs noting which plug lead fits which plug, number them with adhesive tape.
    • With a small/medium screwdriver insert it gently into No1 cylinder and support the screwdriver whilst rotating the crankshaft pulley slowly until you feel the piston rising and touching the screwdriver. Continue turning slowly until the piston begins to go down. you will have hit top dead centre and started on down.
    • Look down at the rim of the crankshaft pulley you should find an engineered mark on it (a torch may be useful here) which should be adjacent to another mark on the timing case housing or the engine block, when these marks are aligned you have top dead centre.


  • Rotating the Engine. There are a number of ways. Maybe you can reach the crankshaft pulley bolt with a wrench.
  • Again with a manual transmission, the engine can be rotated by placing it in a high gear, removing the right rear wheel and levering it using the wheel bolts and a long iron pipe.
  • You can also use a soda straw sticking out of the spark plug hole. Trouble is that there are several degrees of crankshaft rotation where the piston remains stationary.
  • Tighten up the alternator and try a wrench on that.
  • If the oil jar is attached to the car somehow and if it's a manual transmission you can put the transmission in 3rd or 4th gear and roll the car back and forth.


  • Best to disconnect the battery before you start huh?
  • keep fingers away from moving parts whenever possible, or they may be disconnected.
  • Do not turn your engine backwards! Do not. That can cause a loss of timing between crank and camshafts.

Yes you can turn an engine backwards. As long as the Timing chain, belt or gears are still installed. See How to Degree a Camshaft. The engine must be rotated backwards 360 degrees.

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Categories: Car Maintenance and Repair