HEI Distributor mechanical advance curve options

[70GS455]

    So I've found some more information about these centerplates and weights that is helpful. Mainly that the stamped numbers go up for Chevrolet, Buick, and Cadillac, and numbers down for Oldsmobile and Pontiac.

 In other words, if your distributor rotates clockwise, the numbers face upwards.

 If your distributor rotates counterclockwise, then the numbers face downward.

 That's the way the factory designed it, and after testing each centerplate/weight combination, with numbers up and down, it's obvious that you get much better results with everything set up like the factory designed it.
 
 Almost every one of the combinations performed poorly when I set it up with the numbers down, or opposite of what the factory position is. Most every time the weights did not retract fully into position, leaving them flopping around, so there's no way the advance would return to the minimum setting using just the springs.


  I'll post the results of my tests in the next couple of days. It's not a lot, I only have 7 centerplates and 6 different weight numbers, but it gave me a good idea of which set I need to use to get my timing dialed in to the optimum setting, that being a WOT setting of 36° maximum centrifugal advance, and a cruise timing of 52° all in with vacuum and centrifugal advance.
 Im gonna go with manifold vacuum, and advance unit with 16°, and an initial timing of 10°. The vacuum advance starts pulling at 4", and is all in at 10".

  Something else I noticed is that depending upon which centerplate you use, they can change the position of the rotor in relation to the distributor shaft by a few degrees. I saw this when changing the centerplate and would have to reset my gage to compensate for the change.
 

 I still will need to run the engine to see what the advance curve will be, and I can adjust with springs to get it into the rpm range I need.

 On the vacuum advance units, I figured out how to find out how many degrees it will give you. Most of the GM originals have the degrees of advance stamped into the mounting bracket. Using this, I measured the distance from the edge of the shaft and the edge of the opening where the shaft stops. Each .013" is equal to 1° of advance, so if you've got an aftermarket unit that doesn't have any stamping on it, and you want to know how much advance it will provide, you can measure the gap and divide by .013". So for example, if it'll move  .250", then it will advance the timing by approximately 19°, give or take a degree.

  Hope this helps some.
     Rick

Coil + goes to 12v supply. Coil - goes to the HEI module terminal that doesn't connect to ground. Coil HT to a plug. Plug strap to ground

[77cruiser]

I had a stone once, don't ever want another, didn't end up in the hospital, but I had a spasm in my back for a few weeks.

[Cadman-iac]

 
Quote:
Coil + goes to 12v supply. Coil - goes to the HEI module terminal that doesn't connect to ground. Coil HT to a plug. Plug strap to ground.
 Quote:

 That looks like it would work just fine on an open HEI.

 It kinda reminds me of something I did on a 50 year old single cylinder 15hp cast iron Briggs engine after the original coil ended up toast.
 I took an old Mallory coil and wired it into the points. Now it just takes a bump on the starter switch and it's running like a scaled ape, well, for a 50 year old ape anyway.

 Thank you very much for your help on this, im getting out of the hospital in the morning,  so I'll be giving this a try.

 Rick

[Cadman-iac]

I had a stone once, don't ever want another, didn't end up in the hospital, but I had a spasm in my back for a few weeks.

 Hey cruise,

 Yeah, unfortunately this wasn't my first go round with kidney stones. Had an episode about 2 years ago and passed almost a dozen, thankfully very small ones.
 This time I wasn't so lucky. I went to the ER on the 25th, and they shipped me off to Tucson in an ambulance, and by the time they had me stripped and wired, i had quit talking altogether, and my wife says that they put in a tent between kidney and bladder.  Gotta get that out in the next week or two.
 This thing kicked my butt! Supposedly I'm going to be extremely tired for a few months from what the doc says.

 I just told the wife that I was getting fat anyway, so decided to develop a stone to lose weight. I don't think she bought it, but its my story and I'm sticking with it,  lol!!

[Burd]

He has 2 dist machines. I haven’t seen him in a while, the Pontiac Dustoff is soon, I’ll see if he still has.

[DJD OLDS 4MC]

Hi

I've got an Allen distributor machine. According to what you posted, you want total mechanical timing to be 36 degrees at the crank with an initial advance of 10 degrees. So you're looking for about 24 degrees of mechanical advance at the crank. If you post the centerplate and flyweight numbers you have in your collection, I'll look and see if I have any of them here. If I have any of them, I'll run them up in a HEI test distributor and see whether any of the combinations will give you the 24 degrees you're looking for.

Flyweights had two different hole sizes - please indicate whether each set is small or large hole and whether the flyweights are flat all the way across the top and bottom surfaces or whether there is a raised shoulder around the flyweight pivot holes.

Also, what engine are they going into - does the distributor spin cw or ccw.

[Cadman-iac]

Hi

I've got an Allen distributor machine. According to what you posted, you want total mechanical timing to be 36 degrees at the crank with an initial advance of 10 degrees. So you're looking for about 24 degrees of mechanical advance at the crank. If you post the centerplate and flyweight numbers you have in your collection, I'll look and see if I have any of them here. If I have any of them, I'll run them up in a HEI test distributor and see whether any of the combinations will give you the 24 degrees you're looking for.

Flyweights had two different hole sizes - please indicate whether each set is small or large hole and whether the flyweights are flat all the way across the top and bottom surfaces or whether there is a raised shoulder around the flyweight pivot holes.

Also, what engine are they going into - does the distributor spin cw or ccw.

  That would be fantastic, thanks. I am however in the middle of making my own distributor tester to do just that, since my initial testing method yielded less than optimum results.
 I had tried to use an angle protractor to measure the amount of degrees the shaft rotates as the centrifugal advance is activated. Initially, it looked promising, however, once I picked a combination of center plate and weights, from what i have available, the yielded results in the engine fell short of the previous bench testing.
 I don't have any pictures of what I've done on the distributor as of yet, but will post some once I've got it working.  Im basing it off of the pictures that 70GS455 had posted.
 I now have the distributor itself set up with a scale and a pointer, just need to wire in an external coil and set up a timing light and a tachometer, which hopefully prove easier than the first part to accomplish.
 It's been a bit slow going as I've just recently been released from the hospital after a 10 day stay for kidney stones and sepsis, 4 days on a ventilator, so stamina is in the toilet so to speak.

 To answer part of your question, I've got multiple distributors, both large and small pin weights. There's 7 center plate numbers, and 6 weight numbers. My notes are currently in the garage, and i just woke up of course, 3 am now.

 Plate numbers from memory i believe are,; 368, 370, 373, 444, 469, and 482, the last one I can't remember.
 The weights are; like pin 60's,  LG pin 053's, sm pin 106's, sm pin 291's, and I believe small pin 105's.
 The 60's weights are the only ones that have a raised boss around the pin holes.
 I did some preliminary testing on weights to see what if any difference in actual weight was there as well, and the only thing I can find is in the actual shape of the particular weights as compared with each other. There is scarcely any variation in the amount of weight, and i used a jewelers scale in order to get as fine a measurement as possible.
 The biggest difference is in where the weight is placed, meaning closer or farther from the pin location in order to facilitate its activation.
 But I'm getting sleepy again, so will continue aotagain later.  Thanks for your offer, and I will take you up on your offer, if you don't mind just verifying my results.

 Rick

 Edit: Almost forgot, it's on an 88 350 Chevrolet, clockwise rotation.

[DJD OLDS 4MC]

Hi

Good luck in your recovery. I too have been through the agony of kidney stones.

When you're feeling up to it, please confirm the numbers you provided and I'll see what I can find out.

Also, keep an eye on Facebook Marketplace. My son and I were able to pick up an almost brand new Allen machine that wasn't working for less than $200 from an antique dealer in a nearby town. After replacing the ignition coil and one of the meters inside it, it works flawlessly.

Again, good luck in you endeavors and recovery.

DJ

[Cadman-iac]

  Ok, got my notes to be sure I have the correct numbers.
 So the centerplate numbers are 368, 370, 383, 422, 444, 469, 482, and I have a 402 in another distributor that I have not pulled and checked yet, so there's actually 8 centerplate numbers available.
 
 Now the weight numbers are as follows,  large pin weights  #053, #60 ( with pin bosses),  and #139.
 Small pin weights numbers,  #105, #106, and #291.

 I've also got two sets of those cheap aftermarket plates and weights, the weights are useless, but I might be able to use the centerplates after testing.


 One other thing I've noticed is that if you take all the centerplates and stack them using pins that match the mounting holes, you can see how GM shaped them for the various advance curves. There are several that don't really have any discernible differences between them,but some are very obvious as to the difference.

 I'll try to remember to get some pictures to show you the differences between the centerplates.

 The weights are also only slightly different from one set to another, not really in the amount of weight, but in the actual shape of the weight. Some appear to have more material towards the rear, or outer end, which i believe makes them deploy quicker,  whereas the ones with more material near the pin end would deploy slower.

 No pictures available at this time, but will post once my tester is finished and working,  hopefully.

 Rick