Camshaft timing when the sprockets are ONE tooth off from straight up.
It'll push a straight section of stiff chain straight UP, - till it finally flops over, - a tooth over from where it should be .
So that's how it happens!!! I've taken 318s apart and found the chains like that, but never knew why.
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On another note;
Many years ago, mid 70s, my BIL called me up, (he knew I worked on cars) and said his 71 Demon 318, (plastic toothed gear) wouldn't start, at 20(or so) below.
So I just figured he needed a boost. Not so.
After plugging in the block heater for several hours, charging the battery, and restoring the ignition timing; this 318 eventually fired up, but needed even more idle-timing; but it wouldn't stay running unless the throttle was wide open, and then, the rpm was like 500. I soon found out, that the cam-timing was out.
Popping the cover, sure enough, the chain had jumped over several torn-off nylon teeth. I counted the teeth, but in the nearly 50 intervening years I have forgotten. I have a number in my head, but it seems impossible.
It had ran normal the night before.
In this case, the cam was severely retarded, so I just always thought that it had happened at start-up of the frozen engine.
Several years later, I inherited that car. I fixed it up and started "renting it out" to my little brother and his friends. Made some good coin on it, back in the day.