Author Topic: HEI Distributor mechanical advance curve options  (Read 12711 times)

Offline Cadman-iac

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Re: HEI Distributor mechanical advance curve options
« Reply #30 on: April 12, 2026, 05:19:53 PM »
 Not sure if it has any bearing on the total advance or not, but can a weaker set of springs allow the centrifugal advance to continue to advance beyond what you would normally see, or do they only allow the centrifugal advance to reach maximum advance quicker than a stiffer/stronger set will allow?
 
 Im not sure if im incorrect in my thinking here about smaller /weaker springs, after reading so many different points of view over time, i just want to get this straight in my head.

 Rick

Offline Cadman-iac

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Re: HEI Distributor mechanical advance curve options
« Reply #31 on: April 13, 2026, 06:28:35 AM »
And as promised,  here's a picture of what I've been doing to build a distributor advance machine,  at least as far as the distributor end of it goes.

 I used a protractor that I got from Harbor Freight because of its size, it should make it easier to see once everything is working.


 The base, or mounting for the unit is an old adapter tool that would turn a hand drill into a drill press,  it's an old Dayton that I've had for over 25 years, and I've almost thrown it out about a dozen times, but each time I think, Murphys Law will catch up with me if I do.

 If you think it looks a little odd, you're right, I turned the adjustable head upside down so that the drill points upwards, and the distributor will sit above it once I've figured out exactly how to mount it.

 Then I'll make a control board to mount the coil, any switches necessary, and the wiring needed to make it work.

 Once I figured out exactly how I would mount the protractor to the distributor, it was a matter of cutting and drilling everything for clearance.  I also needed to add a reinforcement to the protractor itself to steady it as once I started to spin the shaft the whole thing began to vibrate.  So a small piece of aluminum plate was all that was needed to stop the vibrations.

 I started by first removing everything from an old distributor housing so that I could determine exactly where the mounting screws are located for each part, as I wasn't sure which ones I would have to use initially.

 More to follow as things proceed. Just wanted to show my progress so far.
« Last Edit: April 13, 2026, 06:40:09 AM by Cadman-iac »

Offline DJD OLDS 4MC

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Re: HEI Distributor mechanical advance curve options
« Reply #32 on: April 13, 2026, 08:52:13 AM »
Hi

Weaker springs will allow the advance to begin at a lower rpm, but will not increase the total advance available for centerplates and flyweights I tested. The combinations were taken to 2000 distributor rpms (4000 crank rpms) to make sure all the advance available was extracted.

Offline Cadman-iac

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Re: HEI Distributor mechanical advance curve options
« Reply #33 on: April 14, 2026, 03:00:07 PM »
Hi

Weaker springs will allow the advance to begin at a lower rpm, but will not increase the total advance available for centerplates and flyweights I tested. The combinations were taken to 2000 distributor rpms (4000 crank rpms) to make sure all the advance available was extracted.

 That's what I thought, but I had also read that a weaker spring could let your weights continue to advance, at least if your center plate is upside down from the factory setting.
 In the correct position, I wasn't sure if this was also the case.
 Thanks for posting.

 Rick

Offline Cadman-iac

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Re: HEI Distributor mechanical advance curve options
« Reply #34 on: April 14, 2026, 03:16:40 PM »
 Ok!!!! Well my preliminary tests show that I've got everything wired correctly, and the timing light goes off like it's supposed to, so it looks like the only thing left is to figure out exactly how to mount the distributor to this drill press tool.

 I did notice that an aftermarket ignition module, although it is good and the vehicle ran on it, in this test situation it does not put out as big of a spark as a factory ignition module does.

 That was also something that I had read earlier, so thought I'd swap to a factory module and see if there was any truth to that. Yes, it's true.

 
 Now, something I'd like some help with, as it's set up, the spark plug fires 8 times per revolution of the distributor shaft. Which is ok, except it makes trying to pinpoint the degree of rotation on the distributor for a particular plug rather difficult. 

 Can anyone tell me how to break this down a bit? Right now it's like trying to check your timing with your timing light connected to the coil instead of the number one plug.
 Is there any way to isolate a particular spark?

 I thought about taking an old pick up coil and an old timer core and cutting/grinding off all but one point, but I'm not sure if that'll work, or if I'd just be ruining a coil and core.
 Any thoughts anyone?

 Rick