HEI Distributor mechanical advance curve options

[Cadman-iac]

  Im not sure if this is something that would be permissible here or not, but I've been doing some preliminary tests on an HEI distributor using different centerplates and weights trying to determine what degree of advance is possible for the particular parts I've got on hand.
 I had found a chart on another website that gave some of these figures, but most all of them were using just one set of weights.
 I have either 9 or 10 different distributors, but 4 are in various vehicles at the moment, so I'm just using what I have easy access to right now, as this started as an alternative method to climbing under the hood and swapping the parts and then running the engine and using gas to find the parameters for a given set of parts.
 The only drawback to my current method is that I still don't know at what RPM's any given combination of parts gives the best advance curve.
 Im able to determine what the maximum advance is, with the centerplate facing up or down, but the actual RPM's that it begins and ends at will still need to be done on the engine.
 The advance springs are also another variable in the advance rate, which would also have to be checked on the engine.

 I guess what im getting at here is,  would anyone be interested in this limited amount of information for a handful of different centerplate/weight combinations, and would it be permitted here on this site?

   Rick

[novadude]

Sounds like interesting data.

[Burd]

I had mine put in a sun machine, that’s the best way. 

[DJD OLDS 4MC]

All HEI except Oldsmobile - center plate numbers and fly weight numbers face up.

Olds HEI - center plate numbers and fly weight numbers face down.

According to Dick Paterson @ Springfield Ignition, Orillia Ontario Canada

[Cadman-iac]

I had mine put in a sun machine, that’s the best way.

 Yeah,  I'd love to go that route, but unfortunately I don't have access to one or know of anyone that's got one.
 If I found a shop with one, they'd probably charge a fortune for what I'm trying to do.
   But I'm mainly trying to figure out what each combination would provide as far as the maximum mechanical advance, as far as the curve goes, I can figure that out on the engine, and can change springs to fine tune it.
  Im trying to get my timing into the optimum range for both power and mileage, especially since this freaking idiot has started another war and gas isn't going to get any cheaper anytime soon.

 Rick

[Cadman-iac]

All HEI except Oldsmobile - center plate numbers and fly weight numbers face up.

Olds HEI - center plate numbers and fly weight numbers face down.

According to Dick Paterson @ Springfield Ignition, Orillia Ontario Canada

 Interesting, I've been going by information I got from another site that had quoted a guy named Rocky Rotella, and it says that the factory installed the center plate with the numbers down.  I kinda questioned that, since it makes it necessary to remove it to find out which one you have.
 I'm guessing that the Oldsmobile goes numbers down because of the counter clockwise rotation of the distributor, which does make sense.
 Before finding that article, I've always installed them numbers up,it just made better sense to me.
 Another thing I've noticed too, when checking them with everything in place, there's several center plates that don't seem to work well number down, the weights didn't want to retract fully, they seemed to be flopping between the plate and what would be the normal stop point on the weight, if that makes sense.

 You wouldn't happen to have a link to this Paterson guy, or the article he wrote would you? Thanks for your help, it's much appreciated.

 Rick

[Cadman-iac]

  Pontiac also rotates counterclockwise, so wouldn't those also be installed numbers down like Oldsmobile?

 I'm doing this on a Chevrolet distributor, and another one for a Cadillac that'll be used later on.
  These blanket statements, both from Rocky Rotella and Dick Paterson give one reason to doubt, as there always seems to be an exception for one reason or another.
   Rocky Rotella's article doesn't mention anything about direction of rotation at all, at least not in any of it that was quoted where I had found it.
 As for Dick Paterson's that you mentioned, it breaks out the Oldsmobile as being different, and having had a couple, I knew of the difference. I had had a '68 Pontiac back in the 70's, but I had to think about that one before remembering that it was also counterclockwise. ( Learned that in high school after replacing the cap and plug wires one day. Didn't make note of the wire positions before yanking them off. Couldn't figure out why it kept backfiring through the carb, lol)
 I have an older GM unit repair manual for the HEI distributor from around 1975 or '76, gotta look at it again to be positive.  Anyway, one of the pictures does show the weights and center plate somewhat clearly, and I'd swear you could see the number on the center plate. Unfortunately it doesn't mention anything about disassembly of the shaft or the advance mechanism, it was mainly for troubleshooting the electrical portion of the distributor  since at that time it was a relatively new system for most mechanics, and an overhaul of the unit shouldn't have been necessary at the time of printing.

 I did Google Dick Paterson and got his website. He doesn't give much information, other than advertising for his distributors, so I'm guessing he probably doesn't just give out information free of charge.
 Unfortunately, information like this will probably die with him .
 It's one reason why I'd like to post what I can about it for anyone who can use it, like Cliff does here for carbs.

 Rick

[70GS455]

I've seen some DIY distributor machines and it didn't look all that complicated. Just a support structure, a 12 dc motor, dimmer speed control, degree wheel, tach and timing light

[Cadman-iac]

I've seen some DIY distributor machines and it didn't look all that complicated. Just a support structure, a 12 dc motor, dimmer speed control, degree wheel, tach and timing light

 That's a bit more complicated than I'm ready to get into until I figure out what exactly I'm going to do.

 I did a quick search for a distributor machine, not much out there, and what is is way out of my price range.

 Thanks for the idea though, I may have to try that if what I'm trying now doesn't help much.

 Rick

[70GS455]

That's a bit more complicated than I'm ready to get into until I figure out what exactly I'm going to do.

 I did a quick search for a distributor machine, not much out there, and what is is way out of my price range.

 Thanks for the idea though, I may have to try that if what I'm trying now doesn't help much.

 Rick

How about this one, a VS drill motor, vice, plastic compass, timing light

[Cadman-iac]

    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

[Cadman-iac]

How about this one, a VS drill motor, vice, plastic compass, timing light

 That's interesting, I like that idea. I think most vsr drills will turn up to around 2000 to 3500 rpm, (gotta verify that on mine though) so should be enough to get the weights to deploy fully.

 Thank you very much for posting those pictures, that's extremely helpful.

 Rick

 Edit:  How are you triggering your timing light and tach without the cap/coil in place?