Re Curving the Proform Distributor Timing Advance

[Gregski]

So three years ago I bought myself a Proform HEI distributor, with vacuum advance. My truck is a '74 so it predates the factory HEI but I did not intend to keep its points distributor alive. Figure this will be an upgrade.

So just to level set, Proform makes four different black cap HEI distributors for the Chevy Small Block, but as you will see it's really only two styles (cheap and cheaper, lol).

The first style is their cheap line and it has three products in it, same cheap guts just different finishes etc.

PART# 66941BK - BK is for black (this is the one I got)

PART# 66941BKU - same as above but the U is for unpolished

PART# 66941BKM - same as the first one but the M is for Mechanical advance only, so in other words no vacuum can, not so good for street use, so I passed on this one.

The second style is a more expensive GM factory replacement unit with better guts, a melon sized gear (LOL) you know what I mean, and an adjustable vacuum can

PART# 141-682

and this is their Advance Spring & Weight Kit PART# 66948C

[Gregski]

I was running the cheap 66941BK unit and it was doing OK, but today I decided to dust off that Advance Spring & Weight Kit I bought a while ago and install it to see what the fastest advance curve feels like, I think those are the gold springs.

Well this kit is a total piece of junk. I recon you are supposed to use one set of those plastic bushings in the weights, well when I do that the weights are so snug they do not centrifuge out and I get 0 mechanical advance?! Yet without the bushings the holes are too large for the studs and the weights flop around too much, no bueno either.

So I'm ranting about it to see if any of youz have ever specifically used the Proform advance kit and what sorta luck you had with it. One would think that a Proform kit would fit a Proform distributor, imagine that!

[Gregski]

well lets finish beating this horse to death as I spent better part of the day at this... in the end I returned my cheap 66941BKU Proform distributor to its stock configuration which seems to add only 18* of mechanical timing

my current setup is 10* initial + 18 mechanical = 28 total all in at 3,000 RPM and stayed there till 4,400 when I shut her down

I normally run more initial than this but I wanted to work with easy math, plus it seems to like it, and 10* initial plus another 13* (manifold) vacuum advance she's gettin 23* at idle, can't complain

Side Note: this engine specs call for 32* total, and I was getting that with my GM 141-682 which claims to deliver 22* of mechanical advance, before it died

test drive time

[hatzie]

I buy the recurve kits for the springs and plastic bushings. I leave the GM weights in the distributor.

It ain't rocket science to rebuild the stock GM HEI distributors. If the aftermarket housings and shafts are any good you should be able to install GM electrical parts in/on them.

Get quality GM OEM supplier electrical parts... Delphi and AC Delco.

Make sure the end play between the drive gear and the housing is as close to 0.015" as you can get it. Spec is 0.010" - 0.020". Shim kits from Moroso etc are inexpensive.

I posted a howto on another board...

Re-working with AC Delco & Delphi HEI electrical parts and Moroso or Accel or ... mechanical bits is not any more expensive than the cheap Asian knockoff distributors.
Cheap Chinese electrical parts are usually miserable excuses for parts. Delco and a few others have the resources to ride the manufacturers like a $2 horse so they get a quality product. The Chinese manufacturers then sell the rejects to the second and third tier outfits.
If you use quality internals then you'll have a good working distributor that'll last instead of one made from floor sweepings.

Electrical
AC Delco Professional D221 Module pigtail and condenser $15-$20
AC Delco Professional D1906 or Delphi DS10071 four terminal Ignition module $20-$35
AC Delco Professional D1907X Pickup coil for V8 $40-$45
AC Delco Professional D504A Ignition Coil $55-$70
MSD 8416 Brass contact Cap & Rotor kit $30-$40. Red MSD equivalent to the no longer made Standard Blue Streak DR450X cap and Standard Blue Streak DR318 rotor.

If you need them...
MSD 8402 HEI coil dust cover
Standard 6800R Spark plug wire retaining ring
AC Delco-1965864 Distributor shaft drive gear washer with tangs (If yours is missing)
AC Delco-1977937 Distributor shaft drive gear washer without tangs (If yours is missing)
Accel 170072 is a nice foolproof BAT and TACH connector. I'd use one of them if your 40-year-old BAT connector is hammered. You can extract the Packard 56 terminal from the stock BAT connector and the Accel plug and then insert the vehicle wire terminal in the Accel connector. If you don't have a tach just put some heatshrink over the end of the tach wire to cover the open copper end or remove the tach terminal completely from the Accel plug.

Mechanical
AC-Delco 456652 Distributor gear spring roll pin.
Standard Motor Products DG53 or NAPA Echlin ECH DP110 Grease well felt @ $10
AC Delco 1950569 Grease well felt plastic cover ***Obsolete*** If you can't find one and yours is damaged you can likely get away with just using the felt to cover the grease well.
Moroso 26140 Distributor gear shim kit around $9
Moroso 26150 Distributor body shim kit around $9
MrGasket 929G or MSD 8428 advance kit... I usually use springs, E-Clips, and plastic bushings from these kits with the original weights... Usually costs around $10
Accel 31035 Adjustable Vaccum Advance Can... Around $15-$20. BTW If your original advance can isn't leaking then don't replace it... You'll usually be better off with the old part.

Axle grease for the grease pocket at the top of the shaft.

Disassemble the distributor. I don't agree with his assessment of aftermarket coils and modules. It might've been true in the 70's but by the 1980's GM did some work on the ignition coil and module. Delco and Delphi electrical parts will be reliable for a long long time. Most of us are not driving race engines at over 5,000 RPM... more like 2,000-4,000.
http://www.rustynutscarclub.com/HEI.htm

DO NOT LOSE the thrust washer on top of the housing bushing between the bushing and the lower half of the mechanical advance mechanism.
Shown here stuck to the pickup tooth above the snap-ring. I've never needed a pickup coil so I'm not sure if the new coil has a snap ring or not. I'd be careful to not lose or damage the original.

If the bushings or shaft are scored, the bushing is worn into or past the snap ring groove, or the lower advance is seized to the shaft, get another core.

Take a picture or write down whether the advance weight ID stamps are up or down.

Clean the hard parts that you'll be re-using.
I usually blast the body with walnut shell after a dunk and scrub in Kerosene using a bottle brush and plastic bristle scrub brush. I leave it for a couple hours in the sun to dry before it goes in the cabinet. Stuff a cork or Kleenex/TP in the shaft holes to protect the bushings and rinse again with kerosene and a bottle brush and plastic bristle scrub brush when you're done.
The advance weight assembly usually cleans up by hand with Scotchbrite, a toothbrush, and kerosene even when it's rusty.
Any varnish will clean right off the shaft with Kerosene and careful scrub with a toothbrush.
I grease the rotor mount bushing with a thin layer of heavy grease on the distributor shaft.
The cam mating gear, thrust washer, and the shims usually just get a rinse in Kerosene and a dip in motor oil. If the thrust washer is missing get a replacement.

Make sure to replace the crusty grease in the wells under the pickup coil with some high temp heavy grease. There should be a plastic grease well cover and a felt ring. I just fill the wells and put the original back if it's not falling apart and nasty. My distributors didn't look like they'd been on the bottom of the ocean. If you can clean up one of those distributors... I'd put a brandy new NAPA felt in place.

DO NOT REUSE THE DRIVE GEAR ROLL PIN!!!!. The correct replacement is AC-Delco 456652.

You want the gap between the gear and the distributor body to be 0.010" to 0.020"... closer to 0.015" is better. I usually find the end play to be well out of spec. A wider gap will cause erratic ignition timing. This simple setup check causes a lot more trouble than it's worth if it's skipped.
The shim pak starts with the 1965864 tang washer, then shims, then the gear. Don't put the shims directly against the housing.

http://www.youtube.com/watch?v=6BUQuNGaMKk

I've had distributors ride tight against the oil pump... usually with aftermarket intake manifolds. Shim between the distributor and the intake to lift the distributor body til it doesn't hit the oil pump drive. It's supposed to drive the oil pump not push down on the pump drive rod. Spec is something like 0.030" to 0.040". I usually go with "It doesn't push down against the oil pump drive anymore."

If the heatsink paste included with the module isn't in good shape or there's not enough to coat the whole module and mounting pad I use CPU Heatsink paste. I have a tube of Dow 340 Silicone Heatsink Compound that I used on the PMD on my DS4 Injection pump. The DOW 340 paste works great on HEI ignition modules. 3 oz tubes of SuperLube 98003 Silicone Heatsink paste will work fine and are around $6. Whatever you do DO NOT USE DIELECTRIC GREASE it's not thermally conductive enough.

When you assemble the coil and cap;
Be sure to put di-electric grease on the rubber washer but don't get it on the button or the coil contact... usually a pak is in the package with a new Delco coil.
Be sure the coil screws aren't too long or short to tightly cinch the coil to the cap... these should come in the package with a new Delco coil.
Be sure the stamped ground terminal makes good tight contact with the laminated iron transformer core plates.

More large cap HEI re-building info from the Corvette guys at Super Chevy...
http://www.superchevy.com/how-to/130...e-distributor/

[Gregski]

Originally Posted by hatzie

Make sure the end play between the drive gear and the housing is as close to 0.015" as you can get it. Spec is 0.010" - 0.020". Shim kits from Moroso etc are inexpensive.

Thank you bud that is something I need to check and do next time I pull that distributor out, which may be this weekend.

[Gregski]

found this very detailed post on our Camaro cousin site thought I would share, further down the thread you will see a reply from a gentleman who calls himself Dave Ray and starts off by saying "A few observations from both working on, and being on the team that developed the GM coil in cap HEI's, decades ago."

“GM” Style HEI - Aftermarket Weights and Centerplates

a what the hewk here it is re posted...

"A few observations from both working on, and being on the team that developed the GM coil in cap HEI's, decades ago.

The MSD "curve kit" shown, and others that are configured as same, ARE NOT FOR STREET USE. They are for drag racing, where initial will want to be jacked to the moon over a reasonable street setup. They normally deliver 12 crankshaft degrees of timing, and are designed to eliminate the vacuum advance from the timing equation. Once again, these kits are not for street use, only drag racing, with no vacuum advance in use.

Stock GM coil in cap HEi's have options, as in literally, YES< 437 different advance curve parameters for all the weights/center combinations. Finding one that actually works is a trial and error, error, error situation. The ONLY pair that is well documented is later truck/suburban/crate engine and ZZ series package weights 41, center 375. This package gives 22 crankshaft degrees.

Contrary to urban MYTH and outright lie, the "slots" shown that pass through the plate ARE NOT start/limit plates, as the point distributors use, they are simply large enough to allow the free movement of ALL 437 different curve combo's, without interference. MANY, way too many people advise welding them up, adding screws, all sorts of "fixes" to tailor start/limit areas to weight and cente4r sets that just do not work. Simply stated, EACH different weight/center set has in it, three parameters, the actual curve plot, from start to limit, the START point, and the LIMIT point. IF the start point, curve are correct for what you want, and the limit is too high, or low, you have the wrong weight/center configuration, go forth and test, test, test with different combo's, or listen to all the people that insist on NOT doing it right, by jamming screws into, welding up, and other "methods" of creating all sorts of continuing problems with start, limit and curve problems.

MOST of the better aftermarket large HEI's now have adopted the ZZ 41 weights and 375 center package, BECAUSE IT WORKS IN ALMOST EVERY APPLICATION. Only the most radical engines can't use that much curve degrees, and need less curve degrees, along with jacked to the moon initial, and don't make enough vacuum to run a vacuum advance,m not even the Crane adjustable, that works the best, all the way down to 4 in/hg vacuum. Other adjustable vacuum advances don't work lower than 7 to 8 in/hg vacuum.

As far as a vacuum advance degrees stop, the MSD is not even close to a fair one, it pales in comparison to ease of use, and adjustment to the Crane 99619-1 stand alone scroll plate, BUT, Crane does not mount the plate in the correct place on the advance. MSD's stop will work on the end screw, the Crane should be placed on the DIAPHRAGM side of the pull pin, with a single 8/32 threaded hole, drilled and tapped into the vacuum advance mounting bar. then, the Crane stop does the same as the MSD does, stops the pin as it travels into adding timing, without adversely effecting vacuum pull adjustment. In fact, the Crane stop has adjustment in 2 crankshaft degree increments, not just the 4 MSD stops. the Crane adjusts with a single screw loosening, change the stop position, tighten the screw, no taking it off, flipping it up side down, backwards, as the MSD requires.

Once installed, the Crane delivers 10 separate degrees adjustments, along with completely locking out the vacuum advance completely, in one easy to use device. And, it can be used on stock GM type, non-adjustable vacuum advances as easily as it is used on all adjustable ones. Drill one hole, tap it, install the plate, a machine screw and flat washer, trim the excess threads off the screw on the underside of the vacuum advance mounting plate so they don't hit the distributor body and hold the mount plate up, and adjust it as you see fit...done. Change it, loosen the screw, move the plate, tighten the screw, done.

Both the Crane, AND MSD stops do good, in that they separate the degrees adjustment form the vacuum adjustment, or rating on a stock advance, from each other, exactly the way it should be. The Crane just does it for far less money, and is considerably further adjustable than the MSD is, and, mounts very easily with drill, tap, cut excess threads down, done.

Please be aware, I AM NOT knocking the info given above, it is good in so many areas that others have managed to make so muddy and unclear. But, over many years of working on fixing all sorts of different "methods" that just do not work on these distributors, I have seen so many "variations" on coming close to doing it right, from screws, welding, even very close to "mount the distributor up side down in the engine", it isn't even close to funny.

Regarding engines that like excessive timing, in the early days, they would have had distributors like the old Corvette, no vacuum advance, 18 degrees of initial timing, with another 18 degrees of mechanical curve, and variations close to that, because the cams were so radical, with intake valve closing points way far into the piston rise, they literally caused serious mixture reversion up the inlet ports, they needed the CRUTCH of way too high ignition timing, and too low a vacuum level from excessive late intake closing mixture reversion."

and later he goes on to say...

"I have 5 distributor machines in my shop, and a 2.5K psi run pressure tester to run test the ignition systems after I complete the conversions to them.

I never intended for you to feel anything adverse from my post. You did great work, and even in your update.

A few things that are vitally important for the regular HEI:

The point distributors had significantly different slot lengths and bushings to match the engines they were used in. The curve degrees were mostly in the curvature of the center welded to the distributor shaft, and to change a curve, one needed to select the correct slot length, curvature, stop busing, and springs.

One of the "updates" we devised for the large HEI was the long slot length for ALL the distributors, and to put the start and limit points into the actual curvature of the center plate. Since we were aware of so many different specifications for various emissions profiles for so many different GM makes and engine/emissions configurations, the slots were set up do that ANY and ALL curvature/weight configurations would install in ANY distributor, and when turned one way, or the other work for a right, or left hand rotation distributor.

That is where the issues come where some insist on stopping down the slot lengths to change start/limit points. If it doesn't start/limit in the right places, you AIN'T got the right profiles package of weights/center.

Also, ABSOLUTELY ESSENTIAL TO KNOW, large regular HEI's ARE NOT FEEDBACK types, they do not time using a computer. Here is where I get lambasted on this subject. IF THE HEI HAS MECHANICAL AND/OR VACUUM ADVANCES, DO NOT USE A "DIAL BACK" FEATURE ON A TIMING LIGHT TO SET, READ, RECORD A CURVE, NOR SET TIMING, NO MATTER WHOM SAYS DIFFERENT.

A dial back feature is ONLY for feedback, electronically timed ignition systems on fully computerized engines, such as ones that use Electronic Fuel Injection systems. Dial back is an electronic computation feature that figures timing milliseconds past when a regular system would report a firing event, to give the computer the "lead/lag time" to actually compute the timing event, after receiving and processing the various input information, such as engine heat, throttle position, exhaust oxygen level, etc.

When a dial back feature is used on a direct input system, one with mechanical/vacuum advance, the lag time still exists, and the timing report will be incorrect because of the lag time of the dial back feature. To do a regular system the right way, do what is shown above, degree the balancer, leave the dial back off, and go that route.

We will still have to find time, possibly during the winter snow time, to get into just why we need timing advance curves for our engines. It should be an excellent discussion."

~ dave ray

[hatzie]

Several good posts on HEI on the Pirate 4x4, CK5, G-body, and F-body forums as well. I tried to put as much info on a regular rebuild in my post.

It makes sense that the mechanical advance in the aftermarket distributors and many advance kits have mostly been geared toward racing applications. You definitely don't want these on a daily driver.

His comment about 437 different advance weight configurations is why I lean toward not changing the original HEI dizzy if at all possible.

When you get into the 87 and later small cap HEI dizzy the aftermarket units get truly awful. The Chinese tried to re-design the magnetic pickups and made a bloody mess of them.