This simple yet effective tool is essential in determining the top dead center location of the piston during camshaft timing procedures as well as identifying the actual TDC of the timing damper on the crankshaft. Insuring the damper is accurately representing the actual TDC of the piston guarantees that when you time your ignition with a timing light, that you are really setting to the actual number you are intending to. Setting your timing to a critical number and not knowing the actual timing is really only a few degrees off could result in a significant horsepower loss as well as possibly resulting in severe and permanent engine damage costing thousands of dollars.
Simply screw the tool into the spark plug hole and adjust the center bolt into the cylinder. Then turn the crankshaft backwards and forwards with a breaker bar until the piston gently is stopped by the bolt. Then mark both stopping positions on the damper. Top Dead Center is located EXACTLY between those two marks. Check that location with the imprinted indicator on the damper and remark as necessary.