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When i sped it up, the rotor would move to the right of the terminal by about a 1/4" at first then come back to line up with the terminal.

when i let off the gas from revving it, the rotor goes about 3/4" to the right of the terminal as the motor slows down and then quickly returns to dead on the terminal.

Whats loose?

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is the plate moving around in there?

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Pull the distributor cap off and twist the rotor clockwise and CCW. Not to the point of going into the advance springs but try to feel for slop in the oil pump to dist drive.
How is the timing chain?

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I think you nailed it that this is the "movement" that he is seeing at idle, that they both can(& do)make the rotor & therefore the timing marks jump around at idle. I used the collar on the dist shaft & a good chain & marks are rock steady now

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Pull the distributor cap off and twist the rotor clockwise and CCW. Not to the point of going into the advance springs but try to feel for slop in the oil pump to dist drive.
How is the timing chain?

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I think you nailed it that this is the "movement" that he is seeing at idle, that they both can(& do)make the rotor & therefore the timing marks jump around at idle. I used the collar on the dist shaft & a good chain & marks are rock steady now

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If there is no vacuum to the advance mechanism, that plate is not going to move.

Pull the distributor cap off and twist the rotor clockwise and CCW. Not to the point of going into the advance springs but try to feel for slop in the oil pump to dist drive.

How is the timing chain?

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Pull the distributor cap off and twist the rotor clockwise and CCW. Not to the point of going into the advance springs but try to feel for slop in the oil pump to dist drive.
How is the timing chain?

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I think you nailed it that this is the "movement" that he is seeing at idle, that they both can(& do)make the rotor & therefore the timing marks jump around at idle. I used the collar on the dist shaft & a good chain & marks are rock steady now

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I think that may be it. I did this last night when I first saw the rotor moving and ya, I can move the rotor back and forth quite a bit before getting into the mech advance. I do have a collar on it btw but my distr and oil pump drive are both used- probably got some slop (also two thinks I didn't replace when I built the motor last summer)

I'm going to try and video it. It's unreal

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You think you see the rotor moving back and forth but that doesn't mean that it is actually moving. You are using a timing light as a strobe correct?

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Try a different timing light and see what happens.

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So i starteds it up and fired a timing light at it. it was dead on at idle. every now and then i see what looks like a flash of the rotor way to the right. not sure bout that

When i sped it up, the rotor would move to the right of the terminal by about a 1/4" at first then come back to line up with the terminal.

when i let off the gas from revving it, the rotor goes about 3/4" to the right of the terminal as the motor slows down and then quickly returns to dead on the terminal.

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(1)My light acts like that when I have a poor(light) connection or maybe crossfire (2)"Comes back to line up with the terminal" if this is when you let it go back to idle its normal (3)it is not 3/4" to the right(its less than that) but goes out that far when you let off the gas? So you let off the gas & it advances(more CW)? If so that sounds like the classic increase of adv with vac adv but you dont have vac adv. bottom line is it missing at any point in time & with it dead center at idle it will always be moving more CW & is it moving enough to cause you a problem. I like to extend the rotor tip w solder & have the tip more CCW so the dist terminal is more in the center of it's range of travel. I'm picky I want everything perfect as the chebby/furds guys will not be so meticulous

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The rotor position(seen w the strobe light effect) is going to change constantly as the rpm changes(until you(at higher rpm's) hit the point where the curve is maxed out) & thats normal. I was thinking that the rotor was dancing at idle which would indicate tchain or intermediate shaft slot clearance or less likely dist shaft runout.

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If you are sure the advance plate is not moving around, it seems to me at least two possibilites are:

A triggering problem in the light--not likely, but not unheard of. Is this a delay light?


Worn/ loose shaft bushings allowing the shaft to move in relation to the pickup. With the Mopar aluminum housings, this used to be a huge problem, and is why I eventually ended up with a Hemi dual point which has a ball top bearing (tach drive)

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At lower speeds you can have bounce especially at idle. This is normally the combination of the chain slop and the mechanical advance bouncing because of it. There is not enough constant rotation at idle on the cam and it can actually want to turn the cam the other direction for a split second during idling. On some cars with big springs and low vaccuum this will happen several times a second at idle. On many cars you will see this happen for a split second as you give it throttle and when it initially maintains an RPM. If you check the timing with the timing light this will coincide with it, and although people will argue this, this is not necessarily a problem unless it is extremely bad and happens at mid to high RPM. It can be impossible to remove this bounce completely and converting to a timing belt with a tensioner can help.

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• Turn engine over until you see the rotor move.
• mark the balancer at this point.
• Now turn the balancer the other way until you just see the rotor move the other way. This is ~ how much slop you have to the distributor.

• check the timing at idle.
• Check it again at its highest point.

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i know i have slop. but the check i am doing wont see that. the light will fire when the reluctor passes- WHENEVER the reluctor passes. The rotor's position inside the cap gets illuminated by the timing light.

and slop in the distributor wont change the relationship of the rotor to the reluctor except for slop in the rotor to shaft or if there was any slop in the reluctor to the shaft (but its tight there).

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And the rotor in relationship to the reluctor will change when you have mechanical advance.

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Why is there a slot?

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And the rotor in relationship to the reluctor will change when you have mechanical advance.

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i disagree. both the reluctor and the rotor mount solidly to the same shaft. they mount to this (see pic). When one moves, the other moves right with it. As the weights fly out and move the reluctor, the rotor tip changes with it.

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