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One part of setting the ignition timing is to rotate the distributor correctly. On a 6 cylinder engine, there are 6 sparks per revolution of the distributor, which need to correspond to the correct cylinder spark plug at the right point. This is done by rotating the distributor. To help with this, there are marks on the harmonic balancer that show how far the number one cylinder is from top dead center (TDC), which is when the piston is at the top of the cylinder on the compression stroke. That is, the gas and air mixture is ready to get some fire from the spark plug and do some work. With an automatic transmission, the setting for the 196 OHV timing is 10 degrees before top dead center (BTDC). This means that 10 degrees before the piston gets to the top of the compression stroke, the spark is started at the plug. It takes a bit for the explosion to start and hit the piston on the downward stroke, wich is why you start before the piston is even in place. This is fire, not electricity... electricity travels at the speed of light. If you start the spark too far before TDC, then the engine will backfire, because the piston is on its way up as the explosion hits the face of the piston. If you start the spark too close, or after TDC, then you lose power, and perhaps the fuel/air mixture isn't even compressed enough to ignite at all. The first step to adjusting this, assuming the engine runs, is to loosen the distributor. There is a bolt that holds the base of the distributor to the block:
After the distributor is loosened, hook up a timing light to the number one cylinder as shown in the picture (the farthest forward plug wire), and point it at the pointer next to the harmonic balancer with the strobe on. Look for the mark that indicates 10 degrees BTDC:
Rotate the distributor until the pointer aligns up with the mark on the harmonic balancer:
Once the pointer aligns up with the correct mark, tighten down the distributor hold-down bolt. Note that the timing can sometimes change as you clamp down the distributor, so double check.
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