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It retards timing (steady rpm) and increases spark scatter.
That's pretty much what I figured and was told by the old man, but can someone explain how it does'nt mess up the whole thing. He is unable to explain it to me in a way my simple mind can grasp. I would have thought that when it starts falling behind due to the worn teeth of the gear that it has now lost its place from where it was initialy set, but this does'nt seem to be the case as if runs fine except for on the top end of the quarter mile where we are down a few mph.
Worn gear was discovered due to a manifold change, wonder how long it would have taken to figure out.
Are you sure it is the actual gear teeth that are worn? On my old dist. the spacer bushings/shims wore allowing the shaft to move up and down. That could effect the timing and mine was chewing up the cap and rotor.
Worn gear teeth (either component) allow backlash [slop] into the gear mesh. Thus, the timing can wander a bit. If the wear is consistent between all teeth, timing will not drift as long as engine RPM are increasing due to the gears maintaining mesh on the 'drive' side of the gear teeth. But, when RPM begins to decrease, the gear teeth separate (due to the wear on them) and the timing shifts. Any steady speed will show the timing to be erratic as the gear teeth move [back-and-forth] between 'coast' and 'drive' side of the teeth. Keep in mind that the distributor gear is relatively small in diameter, so wear in the gear translates to timing error pretty quickly.