Locating Top Dead Center
Locating Top Dead Center is important. Most engines will come with either a Timing Mark or a Timing Tab on them; however it is always a good idea to verify this to be certain. Whether it is to replace a distributor, get spark plug wires in the correct orientation, or install a new camshaft, having the rotating assembly on TDC is crucial. While there are several ways to locate TDC, this article will highlight a couple of the more commonly used methods.
The first method is often referred to as the thumb method. Remove the #1 spark plug and place your thumb over the hole. Rotate the crankshaft with a breaker bar and the appropriate socket. As you approach TDC there will be an increase in pressure that will push your thumb off of the port. Once this happens you can look in the spark plug hole and move the crankshaft back and forth to get as close as possible to TDC. This will get you within about 15 degrees of TDC; close enough for a distributor or spark plug wires, but not close enough for that new camshaft.
A second and more accurate way to locate TDC is by using a Top Dead Center Indicator. Screw the indicator into the #1 spark plug hole by hand, and then slowly rotate the crankshaft by hand until the piston come up against the stop. Mark your balancer with a marker, and then slowly rotate the crankshaft by hand in the opposite direction until you come up against the stop again. Mark your balancer again. Measure the distance between the two marks and divide by 2. This is your TDC. Once you’ve found your true TDC why not mark it with a Timing Tape? Speedway Motors offers an MSD Timing Tape with 8 different balancer tapes, so you’re almost certain to find the one you need!
If the cylinder heads are off you can use a similar approach as the Stop Method described above. You simply bolt a strap across the face of the block, and rotate your crankshaft until piston 1 comes up against the strap. Mark that spot, then rotate the crankshaft in the other direction until it again comes up against the strap. Mark that spot and split the difference.