[MartyVi]

Seems to me that the weights in the Pontiac HEI are same orientation as a Chevy for clockwise rotation. How would they advance that way ?
Also I looked at an old Pontiac points distributor and the weights are positioned that makes the plate move clockwise which is advancing timing against the ccw rotation. Yet when I looked on EBay at old used 75-80 hei distributors they were flipped in the opposite direction. Hope you understand what I’m asking.

[PontiacMatt72]

A picture is worth a thousand words…

[MartyVi]

So here is a pic of an aftermarket on left. Second from left is original 1974 hei. Next two are from later year Pontiac hei. Correction on my part the advance moves in the same direction on all of these but the weights are oriented diffidently and you can not just flip them over as they don’t fit.

[mysticmissle]

I don't know if this helps and its vague lol, but i installed a ''crate 455" for a gentleman nthis year and it had a proform distributor that he stated, pulled timing when it reved. it was an odd situation, as i did the mechanical work, but did not want to get involved with any crate motor provider issues, as it felt he was shooting from the hip with potential causes to some issues. Car ran well, but not up to expectations. anyway, i ended up sending the owner a late model HEI and all his problems went away once it was installed. he reused the cap rotor wires etc, but infact would have changed weights with the body as you described. I suspected something wrong with the adjustable vac canister, but again didnt want to get in between the motor provider and the motor purchaser.
Reading your post makes me consider this as a possibility. is it a proform distributor?

[Formulas]

Pontiac HEI cams go numbers down for intended OE useage


timing pulling back with RPMs

Happened to me once

I had a Hays mag pickup that i altered to work with Crane Hi6 CD box got it all together of course checked timing / curve... noticed timing going away with RPM...

I had wires reversed from the mag puckup after i swapped them around it acted right

[MartyVi]

[QUOTE=mysticmissle;6534120]I don't know if this helps and its vague lol, but i installed a ''crate 455" for a gentleman nthis year and it had a proform distributor that he stated, pulled timing when it reved. it was an odd situation, as i did the mechanical work, but did not want to get involved with any crate motor provider issues, as it felt he was shooting from the hip with potential causes to some issues. Car ran well, but not up to expectations. anyway, i ended up sending the owner a late model HEI and all his problems went away once it was installed. he reused the cap rotor wires etc, but infact would have changed weights with the body as you described. I suspected something wrong with the adjustable vac canister, but again didnt want to get in between the motor provider and the motor purchaser.
Reading your post makes me consider this as a

possibility. is it a proform distributor?[/QUOTE

Not Proform. Just another generic aftermarket. But the factory HEI from 75 and up did the same thing flipping the weights over. I think the copy cat aftermarket did that because of what they saw in those factory HEI. Just wondering how that affects the advance timing because one swings out from top outward and the other swings from bottom outward. Hope you can understand me if you study the pictures of the two different distributors.

[steve25]

Here’s the proper orientation of the stock center plate and weights .

[MartyVi]

Thanks Steve.
Like the photos show some are in one direction and others are as if the weights were flipped over but that does not fit.
I took a pic of a 1965 electronic ignition for a Pontiac and the weights are same as my 1974 TA.
Thank you to all that replied.

[MartyVi]

Here’s another pic of the 1965 electronic distributor.

[MartyVi]

Seems to me that around 1975 GM made a change. Maybe they started using the Chevy weights and plates on all HEI. Don’t really know.

[bhill86]

I’m not an expert, and I don’t know WHY the change was made but are you (original poster) asking how both orientations can achieve advance on a CCW rotating distributor? While only ever having later HEIs in hand I think I spotted the difference in the pictures.

[MartyVi]

Originally Posted by bhill86

I’m not an expert, and I don’t know WHY the change was made but are you (original poster) asking how both orientations can achieve advance on a CCW rotating distributor? While only ever having later HEIs in hand I think I spotted the difference in the pictures.

Yes was curious if there’s a difference in how quickly the timing advances between the two different layouts.

[bhill86]

That I can’t answer. I’d imagine that would be determined like any other setup by spring tension and cam design

[Schurkey]

Centrifugal weights (flyweights) swing outward whether they're pivoting from the front or from the rear. Many HEI applications have the weights pivoting from the rear which freaks some folks.

[MartyVi]

Originally Posted by Schurkey

Centrifugal weights (flyweights) swing outward whether they're pivoting from the front or from the rear. Many HEI applications have the weights pivoting from the rear which freaks some folks.

I’m always willing to learn. So just curious what was the reason for the change. It’s often said that engineers do things for a reason. I’m just looking for the reason.