Bent Distributor shaft?

[corolaranet]

I am having some issues trying to fix an unsteady dwell with my distributor. At first the dwell was bouncing around with no pattern. This led me to buy another distributor (a discount rebuilt unit from rockauto) that had the same issue. With both distributors the timing was bouncing a few degrees on idle. It seemed like the bushings were bad, so I changed them.

After installing the re-rebuilt distributer in the car, the dwell appeared to sweep regularly quit a bit. My idea was the distributor shaft was bent, so I swapped shafts with the original distributor. Now the dwell only sweeps about 1 degree and the timing on the #1 cylinder is very steady. Since the dwell is still not perfect I double checked the timing on the #6 Cylinder. It was about 2 degrees advanced.

Is the only explanation for the timing anomaly a bent distributor shaft?

The car has a stock 1966 low output 273.

 

[icetech]

I am having some issues trying to fix an unsteady dwell with my distributor. At first the dwell was bouncing around with no pattern. This led me to buy another distributor (a discount rebuilt unit from rockauto) that had the same issue. With both distributors the timing was bouncing a few degrees on idle. It seemed like the bushings were bad, so I changed them.

After installing the re-rebuilt distributer in the car, the dwell appeared to sweep regularly quit a bit. My idea was the distributor shaft was bent, so I swapped shafts with the original distributor. Now the dwell only sweeps about 1 degree and the timing on the #1 cylinder is very steady. Since the dwell is still not perfect I double checked the timing on the #6 Cylinder. It was about 2 degrees advanced.

Is the only explanation for the timing anomaly a bent distributor shaft?

The car has a stock 1966 low output 273.

It's rare but happens.. i just had one happen to me, it was so bad i could see the housing moving, i put it in a vice and used a dial gauge and it had like .050 runout.. no idea how. If it gets to be too much hassle talk to @HALIFAXHOPS he lives for distributors and could go through them for you or send you a perfect one if needed...

 

[Don Frelier]

Sure the timing chain is good?

Worn lobes on the distributor?

 

[sam dupont]

I also have a suspect distributor. Points can be felt as the spring is compressed, but it seems to have a similar bind at one spot in a revolution. It had set, so I hosed it with knocker loose, pulled the gear, then chucked it up in a drill and spun the snot out it. It's still better, but I can still feel it when I hold the points open a spin the shaft. Never seen a bent shaft before.

 

[AR67GTX]

I’ve seen dwell and timing marks variance on distributors that have excess shaft vertical play in the distributor housing. Once I shimmed the end play down to something like .008 - .010” play it ran steady. It’s kind of obvious as to why this helps on Chevy distributors with their distributor helical shaft drive gear at low rpm. You would think the tang drive into the lower helical drive gear on a Mopar B/RB motor would make this less of an issue but it doesn’t seem to.

 

[HALIFAXHOPS]

Yes they bend all the time. my limit is .005on the upper shaft zero on the bottom think the book is 8-10 on the upper.. After a bushing change they also have to be burnished to seat the housing right and the dwell has a +/-2 on most. The FSM will walk you right through it. I would see what it actually needs and not throw parts at it they get expensive fast now. I would say 2 out of ten cores I get in have to have the shafts straightened to specs, I usually just toss them and use another one. This one is a classic Came in a lot of cores of unknown condition. I have no idea how it happened or why the housing did not shatter??????

 

[Geoff 2]

Worn or poorly machined points cam will cause dwell variation.

 

[oldkimmer]

Plus the bushing in the block can be worn and have excess play in it. Kim

 

[1967coronet]

Also a cheap set of new points with a weak spring will make your dwell jump around.

 

[corolaranet]

Thank you for all the replies. I was hoping to be able to do some testing this weekend, but the weather did not cooperate with my schedule.

The cam measures fine lobe to lobe so I doubted it is the problem but is definitely worth double checking. Knowing that bent distributor shafts are a thing is good to know. I will be checking that as soon as I can.

How important is burnishing the bushings? I did notice the FSM states to do so, but I do not one such a tool or a press at the moment. To me it seems like reaming would be good enough, as the bushing is a press fit to begin with. I couldn't find any decisive answer to this on google.

 

[HALIFAXHOPS]

Burnishing expands a bushing to ensure they will not shift. Reaming is really to ensure they are in line.
FYI
The bushing resizing tool works by pushing a precision machined burnishing tool through both the upper and lower bushings to resize them and force them into round. This forces the bushings to gently expand to the correct size and shape allowing proper oil flow between bushing and stanchion

Reaming is a cutting operation that involves enlarging existing hole diameters more accurately and enhancing the surface finish of the hole's walls. The reaming tool used for the reaming operation is called “Reamer.” This process is a finishing operation and does not cut much

 

[corolaranet]

That makes sense. I was hoping it would be fine, but its not worth the risk; the shaft is seems bent. Another distributor that was rebuilt properly is the only realistic way at the moment. Before I buy one, the car need some more pressing work done. I will DM you (HALIFAXHOPS) when I'm ready to buy one. Thank you for your insight.

 

[HALIFAXHOPS]

No sweat there is a lot in them that people never experience. Been doing them a very long time so have seen a lot.