bccan

I was at a car show yesterday and my powers of observation determined that appx 80% of the GM “muscle” cars were running HEI distributors.

With some regularity there is discussion about the use of HEI distributors. Over the years & even the last few days I have had experiences and made observations and felt it might be worth discussion in it’s own thread. I have found them to be generally reliable & simple to maintain.

The one time I had an issue a GM HEI my Chilton Manual had very clear diagnostic procedure that led me to a bad “Pole Piece.”

I have had 2 problems with my aftermarket HEI distributor (Mallory 75 Series (built by RobbMc before he went out on his own)) over the appx 13-14 years I have used it. I had picked up pizza & was idling down a side street near my house and engine simply shut off. I called home, the kids & their friends were dispatched the block or 2 that I was short of my destination & they pushed me home. When I got to investigating I found the roll pin on the gear sheared, go figure. My other break down occurred as I drove someone from the NEOC show to the parts store as iirc his alternator died & he had to drive home to MA. We were trolling along in a line of traffic when the car shut off, I rolled to the side, quickly found no spark with one of those inline testers that I keep in the tool bag. Deeper into the trunk I go, pull out my spare HEI (GM), pop it in & we’re back on the move in 10-15 minutes & score a safe journey to parts store, then return to the show & later to our individual homes. Post Mortem found a bad pickup which in this distributor is actually a Ford EEC(?) part. That 75 series distributor is a beautiful piece due to the very flexible mech & vac advance design ( HEI’s Achilles heel), rev limiter & very high quality construction.

The other day my friend was over to visit & at some point he mentioned he has been going through distributor modules. He had driven his 71 Chevelle so I had him pop the hood, sure as heck the OE wire with starter bypass wire was feeding the HEI distributor. I explained what the wires did, voltage, etc & I supplied him with instructions, wire & some spades to hook into “ IGN” terminal on fuse box as he is capable of running the wire.

If you convert to HEI you MUST run a 12v power source, ignition switched, not use the existing distributor power wire.

Probably best not to buy one of those cheapies, buy a good one (DUI would be my first choice AFTER the Mallory 75). The 75 series is hands down the best for the competent tuner, if these are even available anymore & you buy one, do yourself a favor and buy the “keys” for setting mech advance, they make adjustments accurate & easy. The 75 series is totally different architecture & components than GM’s, it is only HEI cap & coil style, the rest is 75 specific. A used GM is still a good choice if it isn’t too beat. The shortcomings of these is that they were designed for emissions control, not performance and are a chore to set a favorable mech advance. The mech kits are limited, the vac advance kits are simple & work well.

Let the observations, experiences, anecdotes and debates begin. It will help people make choices & decisions.

oldcutlass

I've noticed the same thing to include small cap hei's. Seems most people don't run points anymore. I have a model 75 sitting on the shelf that I acquired a while back, I think I'll dust it off and set it up.

Fun71

My experience with extensive experimentation is the Moroso HEI Advance Curve Kit weights and center bar give 24º mechanical advance, so the distributor can be set up exactly the same as a 68-72 points distributor.

I opted to retain the factory 1978-1979 weights / center bar to have a higher initial advance and higher idle vacuum and a smoother idle. I used only the lighter springs from the advance curve kit to bring the total timing in earlier. This works very well with the larger-than-factory camshaft in my engine and I will say it works extremely well for my street performance application.

bccan

If you’re going to put that 75 Series into action do yourself a favor & buy the set of “keys” for setting that YH mech advance. The advance weights are in the lower bowl & get gapped for the limit, that is where the keys come into play, they set the gap based on the max amount of advance you want to set. You can get away without them but you will be back in there multiple times trying to gap the weights. You need to slide off the reluctor(?) wheel & cover plate to access the weights. If you know what your max mech adv is, set it before you put distributor in the engine as it’s a biotch to do in the car, springs are in there too. If you know where you want to be on max’s & curves the best thing to do is set distributor up on a Sun machine.

I know this all sounds like a hassle but it is a really solid, reliable set up & IMO worth it. Open that baby up & check it out as it is a completely different animal from GM HEI, also make sure you have directions for dist & YH advance mechanism. One last suggestion - get a non magnetic feeler gauge for setting the pickup gap, I couldn’t get a good feel gapping it with a steel feeler gauge. If you end up hating this thing, PM me & we’ll make a deal!

oldcutlass

Thanks for the info, I didn't realize it was adjustable and had a rev limiter. I downloaded and read the install instructions, pretty neat unit! But its not very informative on what the gap measurement is for setting the stop to know how many degrees for the mech. adv.. It just states its goes from 0-28* and factory set for 24*. I assume the keys go into the slots that you speak of. I guess I could measure the slots and see what the length is and divide by 28. Where would I get a set of keys since Mallory is no more. I doubt you would have any interest in it its for a BBC.
https://www.carid.com/images/mallory...structions.pdf

bccan

I just searched & keys seem to be extinct. If you decide to play with it I could mic my keys & let you know the measurements,
then you could probably use drill bits if you have a comprehensive set.

Keep your BBC distributor!

oldcutlass

That would be great if you wouldn't mind, I can probably come up with something that could work with some measurements.

bccan

I’ll put it on my list but don’t hold your breath unless you’re trying to get that Chevy out this weekend with that “new” distributor in it!

I didn’t want muck up thread + people don’t need to get sick of pics of my cars.

YH “Key” Thicknesses as measured by fumble fingered auto enthusiast. They are plastic so it might not be me. Spread appears to be typically .0180” except the 14* which I did recheck multiple times.

14* .1330”
16* .1480”
18* .1660”
20* .1850”
22* .2030”
24* .2220”
26* .2420”
28* .2600”

oldcutlass

Not in any hurry, I'll also keep my eyes open for the keys you were talking about. Probably something I'll play with over the winter with all the other projects on the list.

olds 307 and 403

Yeah I have a couple of sets of keys and a few springs for my Mallory Breakerless distributor. I am also running the 6AL box which also eliminates module issues. Getting a tach to work is another story. Really mixed info about which one will work. I have one with the spark plug wire attachment, reads right sometimes. The stock HEI isn't as bullet proof as people think. We have owned multiple vehicles where the pickup coil died. The only time I have killed HEI modules is unstable voltage. The Chinese HEI's seem to be better built than a few years ago. I upgraded the module and coil, otherwise fine with multiple 2.5 hour, one way trips.

oldcutlass

Thanks bccan for taking the time to measure the keys and edit your post.

KW5413

Well, this isn't about my Cutlass but, my '70 Nova (Pre-motor rebuild) had a catastrophe failure of its original(?) distributor back in 2013. Returning from the Hot Rod Power Tour traveling a smooth 70 MPH the BIG BANG and tons of smoke put us on the shoulder of I-30 pretty quick. This was between Hot Springs and Texarkana AR...and I live in far east suburbs of Dallas. Called AAA and my daughter. My Daughter got to us just before the tow truck did. But...I was asking for a roll back that could take the car home forthwith. That didn't happen but, the very nice Arkansas High Patrol stopped by three times to check on us. The last time he told us if we were still with the car the next time he came by he would have to take us somewhere off the highway. He understood why we wanted to stay with the vehicle but, needed us to get off the road. All in all...4 hours. The Tow arrived just as we were getting in my daughter's car.

But, I digress. The distributor was toast so I replaced it with a MSD Ready To Run HEI. Earlier this year it failed. A module failure, as I recall. I replaced that with another Ready To Run. If it dies I will move on with another product. But, I am glad that I moved up to an HEI system. Generally, one less thing to be concerned with on these old cars.

Schurkey

Dave Ray calls 'em "Ready To Die".

They're not an HEI. HEI is/was a trademark of GM. HEIs are electronic ignitions. Not all electronic ignitions are HEI. The MSD unit may put out strong spark--when it works--but it's not the GM HEI design.

A "REAL" HEI is the most reliable ignition system on the planet, if the various bits are OEM quality. But cheap-junk replacement parts--and entire distributors--are so common today that their reputation has suffered. Even decades ago, there were "discount" HEI modules that got people into trouble.

Run to Rund

I am running the MSD distributor with 7AL3 box and it does make the car easier to start after sitting for months. It has been reliable for about 12 years now. I tried the HEI in 1974-75 and it worked well but is a snug fit with Tri-Carbs.