I thought some of you might find this interesting. I went out the other morning to go to breakfast and the car wouldn't start. Tracked it down to no spark and decided to replace the ignition module in my GM HEI dist. with the one that came with the car in 1975! Bingo..started in 1/2 revolution. This is the second time I've had a HEI dist failure, the first time the button fell out from the coil that contacts the rotor. Incredibly, both times it happened in my garage so someone is looking out after me for sure!!

Anyway, out of curiosity I took the thing apart, carefully removed the silicone potting material to see what was inside these things. The second enlarged picture below shows an open component lead which seems to be the culpret. It's located in the bottom left corner of the first image. I guess these things are really prone to failure when used in boats (according to the NAPA guy), must be the high vibration levels. That failed part is attached to a piece of copper bonded to the steel base. My guess is that's what gets hot in this thing and is the reason for the thermal grease under it. I bought a new one and stuck the 1975 version in my glove box

 

May I ask why you would repeatedly spend money on semi-reliable aftermarket modules and only use the unbeatably reliable OEM module as glovebox ballast?

 

I replace my 30 year old HEI with a MSD Streetfire, when the mech. advance was rusted. Did not work any better, but it is shinny.

[IMG][/IMG]

 

I certainly have to respect your honesty and candor.

 

Ha! Well actually that's a good question...I just figured a new Echlin might be more reliable than a 35 year old one but maybe not! The one in the picture that failed is from a GM Performance crate motor.

 

Save that module!!!

 

I would prefer a 35 year old Delco part rather than these brand X modules I see floating around. Aftermarket suppliers can't compare or compete with the amount of engineering and durability testing done by Delco.

 

then again your part is 35 years old and might need to be replaced LOL

 

I admire the poster's inquisitive attitude and his interest in sharing the findings with us. Thanks!

 

I must agree I do like original parts myself ! sometime you get in sticky situations and have no choice

 

WAIT.....what about the MSD module or the ACCEL module?
Are they just Delco's reboxed? I thought they were "High Perf"????

I found an ACCEL unit in my 1981 distributor.

 

Thanks Bill!

 

also !
..............I like it when people take stuff apart.

 

What is your opinion on the MSD modules.? I know it's doing something different because it will fry a stock coil in just a few months.

Onced matched with with an MSD coil its been working for years. Seems i get better cold starts but i could be fooling myself.

 

Well, I can only give a few general thoughts due to a present lack of details on the particular module you are/were using. Glancing through my Summit catalog I only saw one MSD four terminal module (HEI "upgrade"), so my comments relate to what happens if this particular part is installed in an OEM HEI distributor.
The MSD part claims a 7.5 amp primary current rating. This is significantly higher (approx 30%) than the Delco module's active current limit of 5.8 amps (to assure long module and coil life). At low RPMs the available dwell time will allow the primary current to hit the 7.5 amp target, at which point the ignition coil will be dissipating higher wattage with the MSD part. Wattage is obviously heat, and rumors are this extra heat may "fry a stock coil". You'll get more spark energy with the higher current of course, but rarely do systems not supply enough energy at low engine speeds.
Now, at high engine speeds, it's a different matter. Here the coil's inductance is the main determinant of peak coil primary current, and the resulting energy stored in the coil. (Note to newcomers: Nowhere in this description do I mention coil/spark voltage, as that's just a marketing gimmick to hook new customers.) It doesn't matter what the module is calibrated to limit the current to, chances are the primary current won't be able to hit the peak target anyway. So, in this example, the coil/plug energy levels at high RPMs are unchanged from stock.
The module and coil should be electrically "matched". Not only to obtain the desired energy storage, but also to insure system durability. As the MSD module in question allows higher current to flow through the coil windings, a coil that is designed to operate safely at higher currents should be selected. However, that's harder to do than it appears. A wrong choice will result in a coil that stores less, not more energy. It's also entirely possible to inadvertently (but safely) run a low amperage (3A) coil if the inductance was so high that the available dwell time would never allow it to reach high enough amperage to fry. It would also not deliver much energy at the higher engine speeds.
So, this is what "frustrates" me about the ignition aftermarket. Unlike cams, which are supplied with a data sheet indicating all the applicable specs to assist you in making an intelligent parts purchase, the ignition aftermarket is filled with endless bling descriptions and darn little technical information.
JMHO