This one really has me stumped. When checking timing I see that the timing mark on the damper is bouncing. If looking at the damper as a clock, the mark is every between 7 o'clock and 11 o'clock. When it bounces to 11 o'clock it at 10 degrees where I want it. The motor is a rebuilt 361. I already pulled the timing cover and checked the chain and it is good and tight, no slack when I rotate the engine by hand. I also pulled the distributor and the for slack in the shaft to shaft. looks good there. These are all new parts. Any ideas out there? Thanks,, Alex

What ignition? Did you try another timing light?

Its Got MP electronic ignition. and no, didn't try another's timing light. but will tomorrow. Thanks

I’ve had several friends and customers use the mopar chrome or orange ECU. I quit those years ago. And yes, go ahead and flame away and tell me they have sold millions of them. Well, they are made in China now and they could care less about quality. I recently worked on a 68 Charger done back in the early 2000. It had a brand new mopar distributor kit with an orange box. It was never driven much because it had a bad flat spot off idle. He finally brought it back to me to get it straightened out. I used the Petronix system on the last three customers with good results but did have problems out of the points conversion kit with a Petronix III. I talked to Don at FBO and decided to give his a try. His distributor curve fixed my problems with the stumble. The first thing I noticed on both of the cars that I installed them on so far is that my flash on my timing light is much brighter and the timing mark does not jump around. It is rock steady. I’m using it on all my customers cars now.

Mopar Performance has not made the OEM Chrome or Orange Ignition Modules for years

I had that issue. I added a 1/2" locking collar to the distributor shaft and it eliminated it entirely. I did use a dab of loctite on the threads, installed the collar loosely, bolted down the distributor to position the collar and the removed the distributor to tighten the locking screw tight. Reinstalled it and set timing.

Does this work on SBs? Or is the collar only for BBs?

Works on them both

Goodson sells them

Is the description for install above all there is to it?
What sets the position of the collar on the shaft?
Would it be a good idea to hit the shaft with a punch to give the set screw a good spot to seat?

i have encountered bouncing timing marks but have always found that moving the pickup to a different location on the wire or using a different light remedies the issue. I have never heard of this locking collar nor encountered one. Can someone explain how it addresses the issue / works and post a pic ??

I bought mine from Hughes, but they are simply common industrial parts that can be had from Graingers etc. The locking screw does not touch the distributor shaft, rather is constricts the collar so it grips the shaft.

A secondary reason I run a collar is that it dramatically reduced the wear on my bronze gear I used to run on my roller cam. It did that by limiting the intermediate shaft gear climb up on the cam's gear, which also alters the position of the rotor as it goes up and down, ie bouncing timing at idle.

If the intermediate gear is allowed to travel up and down excessively, the contact pattern on the gear's teeth changes significantly resulting in accelerated wear. Once I started running the collars, the wear pattern stabilized and my gear wear dropped dramatically. It also stabilized my timing at idle, as we all know the intermediate shaft rotaes a bit when installed or removed due to the angle of the gear cut. It's attached directly to the rotor, and as the shaft rises and falls when the motor is running, the timing alters slightly. I imagine that the gear is forced downward into the bushing when the motor is under acceleration, but at idle is moves up and down limited only by the tang on the distributor shaft. The motion reminds me of how my driveline "bounces back and forth" when cruising under no acceleration load or deceleration.

Be advised that some clearance between the collar and intermediate shaft is required, or it will wear the intermediate shaft bushing until it machines the clearance it wants. I have just left the collar loose enough and added a small "washer" of paper(like a matchbook cover" just below the collar, so that it positions itself once the distributor has been fully seated. I then re-pull the distributor, loctite the screw, tighten it fully, remove the paper and re-install the distributor. I have not had one move yet. If the set screw comes out, it would be flung into the motor possibly between the gear teeth, so clean the oil off it and loctite it.

Betting you have very light springs in the dist for a fast curve? The newer style MP dist had light springs and they start to advance at around 800 rpm so at idle when your try to set timing the weights are bouncing due to light springs. If you use an advance light and set total timing at 2500 rpm Ill bet timing mark does not move or bounce, if this is the case you need a heaver spring or even both in your dist. Ive got a sun dist machine and see this all the time and a spring cures it.

I think everyone is reading more than what is being said here (till now).
He only says the timing mark is jumping around, not that the engine is running rough or misfiring.

A lack of dist.shaft collar will never cause such a large timing deviation, unless the distr.shaft 'tang' is way too short.

If the advance springs are too light, the engine's idle will be nervous as well. No mention of that yet.
Since it's a rebuild, I would almost presume the original distributor is reused.

The poster has not posted back. As just mentioned this is a new rebuild which reminds me of a case. Customer had a fresh 360 and had erratic timing. End result was no oil pump distributor drive bushing. Only one I have seen and it sure caused issues.

Gotta love it when you try to help a guy and he just blows evryone off. Oh well he is somewhat of a newbie with only 2 posts. next he'll be whining why he gets ignored LOL

And thanks to those that responded to my question

The reason no response from the poster is because we had a serious family issue here! Things don't always go the way we want. I would have otherwise posted a response.
I didn't get to go back to the car till this morning. Anyway, the trouble turned out to be nothing but a malfunction in the timing light.. It has since been tossed in the trash.. Thanks to those who had the patience to offer help without the snide remark.