The Stovebolt Site Forums The Shop Area The Electrical Bay Pertronix failure solved...

Around a year ago a friend sent me a failed Pertronix module (and parts associated with it). At the time I deconstructed the main part, did not discover to my complete satisfaction what happened and today I decided to finally get to the root of why it failed.

Basically the unit itself is a very simple Hall Effect sensor coupled with a resistor of unknown value (it was imbedded in epoxy and was destroyed when I deconstructed it). That wasn't the problem although at the time I suspected it could have been. Not to bore anyone, but a Hall Effect sensor works more/less like a switch when exposed to a magnetic field...and it is important to understand that "switch" will vary in effectiveness depending on the magnetic strength. And what I mean is at a point it will still work okay and then with one hair's less magnetism it won't work any longer at all...that loss of magnetism can be the result of increased distance to the magnet or simply loss in the strength of the magnet. In this instance the distance is a constant, so we have to look at the strength for our answer. That is what I failed to do originally and as it turns out was a mistake on my part.

Pertronix relies on a plastic wheel that's mounted firmly on the distributor cam. Please see image 1 below. This 100% plastic magnetic wheel has 8 sections separated by slits (for a V8, that is). Magnetism from the outer side of each section of the wheel fires the spark plug for 1 specific cylinder and hence the need for slit-provided separation. Just like the simple ignition points approach but magnetically rather than mechanically. About 2mm from the top there is a spring steel ring to keep centrifugal force from deforming the slits in the plastic wheel.

Now please turn your attention to the second image. The red arrow shows where the Hall Effect sensor must receive its magnetic impulse...the narrow zone above and below that line. But unfortunately there is zero magnetism present on the outside of the wheel at that area...all the way around the wheel. I can detect faint magnetism on the back side of the wheel but not on the front side at all. And after removing the retaining ring I notice there is definitely an irregular magnetic field present on the ring...stronger at the ends of the ring. I don't believe it is strong enough to trip the Hall sensor but it is there. The wheel is plastic so I have to think they imbedded the plastic with ferromagnetic iron oxides. Those can retain magnetism for a good while given the right environment but can lose magnetism in the wrong situation and the answer to the question "why" can be complex. When you look lower...to the location of the green arrow you start picking up stronger magnetism on the outer side as well as the inside. In this case, the thing failed quickly. It had been working okay...and then one day the engine died and would not re-start no matter what (a very common complaint with this product). No spark at any plug. I have to think the entire thing was designed incorrectly and I also think the retaining ring somehow caused or helped cause deterioration of the magnetic field needed to make this work.

I think it is obvious loss of magnetism is the cause, and I suspect the engineers miscalculated and simply didn't build those wheels correctly. Either that or they intended them to fail. The wheel should have been designed to last virtually forever (which is why I didn't suspect it at first) but it wasn't. You can make up your own mind as to whether you want to buy one of these and whether you want to depend on it.

Jon, that sort of reinforces my idea that there are two types of Pertronix units- - - -the ones that have failed, and the ones that will fail soon. Another problem I've observed is that the "snug-fitting" trigger usually has at least one degree of rotation slop on the distributor cam, and sometimes as much as two degrees. Every degree of inaccuracy at the distributor shaft creates two degrees of random timing error at the crankshaft. Bad juju!
Jerry

Yep, Jerry. A friend says he thinks it turned the retaining ring into a round horseshoe magnet. Bad juju, indeed!

Jon, my GUESS is, and only a guess, is the wheel is molded. The mixture is a plastic as a moldable "substrate" (ring reinforced) Mixed with a magnetic material. The reason half the people who bought Pertronix like it and half don't is the Chinese molding process yields a non consistent distribution of the "magnetic material". I'm assuming the plastic and magnetic material is resistant to under hood temps with ambient 120 deg Arizona or -35 Alaska.

My theory is based on you saying the magnetic force is variable at different levels/places/segments. Inside different than outside in places. That says inconsistency in manufacture.

I assume you checked every other component to be sure it's the wheel even though you see funny results with wheel magnetism.

You may have a point, Bart however I'm not certain the magnetic wheel was made in China...it could have been but that's not something I can be certain of. And the temperature could have been a problem but as I recall (and this goes back many years but I could dig up the book and verify it) heat is a problem for magnetism but only when the Curie point has been exceeded. What is the Curie point? It is pretty high as I recall...around 1000 (F) is what the recesses of my mind are saying. By interesting coincidence I ruined a magnet while welding a few weeks ago. I was using one to hold two pieces together and the heat destroyed it. I'm sure you know that heating process re-aligns the molecules and turns them paramagnetic. I believe the ferromagnetic particles can be very small (like those on recording tape...which would hint at a better distribution pattern) or large (which would hint at a less uniform distribution...but only a hint). As you'd expect small particles lose their magnetism more rapidly and there will be fewer of them by definition. The fact the retaining ring is magnetized and the field is stronger at the ring's ends makes me think it was (as a friend suggested) becoming a little horseshoe magnet with the ends being the poles. It is magnetized enough that a non-magnetized screwdriver will lift it and hold it airborne...and it would not have been manufactured that way. There would be no need for it. I'm leaning toward the idea the ring has been leaching magnetism away from the wheel (hence the reason the inside part of the wheel still shows magnetism) and that loss extends down as far as the slots have been cut. Sadly I don't have a gauss meter any longer or I could measure to see if the strength declines from the top down. I do know there is no detectible magnetism where there should be. Yes, I did check the Hall Effect sensor back when I de-assembled the thing. Couldn't tell if it was ok or not, but hoping to use all the original Pertronix "stuff" I was checking it with the wheel and now that I know the wheel has lost magnetism, it doesn't matter...there would be as you know nothing to trip it. Whatever the answer if these wheels are losing their magnetism, that's got to be contributing largely to the failure of them. I still would not use one of these in any vehicle. Way too high of a failure rate. Thanks for your comments!

Jerry’s comment about temperature differences is valid. Plastic has a large coefficient of expansion and the wheel could shrink enough to make it lose the magnetic connection when the engine is cold. Magnetism drops off real quickly with distance. I doubt that any underhood temperature is high enough to kill the magnetism. I too killed a magnet trying to weld up a tool.

The more I learn about Pertronix, the better I like the GM HEI system! (Thanks, Jon!) GM uses a magnet that surrounds the pickup coil, instead of a rotating magnet. The trigger on the distributor shaft is a simple piece of steel with as many triangular points on it as the number of cylinders. The dirty little secret is that there can be half as many trigger points and the system works as well, if not better since there are still the same number of corresponding trigger points on the pickup coil core. In other words, three points on the rotating shaft and six on the pickup will still fire six cylinders- - - -there's just half as much induced voltage going to the module. That's why my modified HEI distributors on the race engines would wind 1000+ RPM faster than the competition without getting spark scatter- - - -I ground half the points off the rotating trigger! The tech inspectors were too dumb to catch that little modification on a "street stock" engine, along with a couple of other Smokey Yunick type tricks I used.
Jerry

Kevin, I assumed they would make sure materials were heat reisitant. Meaning I thought that would not be the problem even though in extreme conditions in regional zones starting with x ambient. "Underhood" includes induction from "block" into distributor shaft into wheel. Just a side comment anyway, in my "guess" post. Other guesses from others are relevant and not arguable as such.

The allowed gap is .010 to .060 so there may not be an issue with coefficient of expansion/loss of distance.
The true way to determine if this part is a failure point is to place it in a known working set up on a motor.

Another guess is if there is no fire it seems to not be the rotor if gapped correctly. I'm guessing some firing would occur with mixed strength rotor magnetics. Not Sure.

Most info says magnets are "embedded" in the rotor. I think proprietary issues keep us from knowing what that means exactly. Pertronox started out with bonded magnets and I guess evolved the design when they kept falling off.

Magnets or retrieval magnets or magnetic tip screw drivers can cause rotor issues.

The rotor magnets can get weak. But no explanation as to why.

HAPPY FOURTH GUYS!!

Let me try to show just how devoid of magnetism the upper part (the operative section) of the wheel really is. I cut a thin (<1mm thick) sliver of steel which is at its widest 1mm and 3mm long. A tiny piece. If you look at the first image below, you'll see the first place on the wheel where that tiny piece of metal can detect any magnetism. Above that there is none at all. Far too low to activate the Hall Effect sensor.

And if you look at the second image you will see the metal retaining ring (the one which has become more/less a little horseshoe magnet) happily holding the same little piece of steel airborne. Literally there is no way this thing could have worked any longer. Hopefully this is all anyone needs to see about these to make up their mind.

I'm working on a "home brew" modification to a standard stovebolt distributor to put the GM HEI pickup coil and trigger into it without doing any permanent mods to the distributor housing. Well- - - -maybe a couple of drilled and tapped holes in the breaker plate- - - -nothing that would prevent going back to the original point/condenser system if desired. The trigger module will be mounted to an aluminum heat sink under the dash, away from engine compartment heat and weather exposure.
Jerry

That's a good idea, Jerry and it would appeal to anyone hoping to keep a stock-looking distributor. If you needed to I think you could use Torrington-type needle bearings at the top and bottom of the shaft (machined and pressed in to the distributor housing). Shouldn't be difficult and would help with any wear the shaft may have suffered.

I'm already using a Torrington bearing on top- - - -and a bronze bushing down on the bottom where there's plenty of splashed oil to keep it lubed. That allows the gap between the trigger and the reluctor teeth to be minimized for the best signal generation without worrying about making any physical contact.
Jerry

That makes good sense.

Anyone have experience with one of the Mallory E Spark points conversion systems? Uses an infrared signal rather than the magnetic of the Pertronix.

Yes, but...A friend was going to buy one of those and when he figured out the cost of it all he decided to just get one of the clone copies of the GM HEI distributor and modify it as I showed how to do (on this site maybe a year/year and a half ago). Here is a summary of what he told me about that clone distributor: the coil-in-cap looks different from the original, he said that didn't bother him...he wasn't doing it for the appearance value, he said he was certain the new parts and the precision of the new unit helped, he said it started faster, idled better, seemed to get better mileage, ran without missing and he liked the new vacuum advance unit (his on the old distributor was not working well). He also said he liked the new coil and the lack of coil wire. He said he paid less than $60 for one with a black cap on eBay, got free shipping and then paid about $7 for a shaft collar piece. He said it was possibly the best $70 he had ever spent on the engine and it seemed to run better in the winter (he lives where it gets pretty cold). The one I'm using was bought around 1997. I've never had any trouble with it. I have one of Tom Langdon's mini HEI units, however something went wrong with it after using it for roughly a year and I haven't tried to see what the problem is. It does look more like the original. Uses GM parts, but I will tell you finding those that are not made in China, Portugal or Mexico today is not easy. I will encourage anybody considering any of these type conversion schemes to check the play (shaft to body) of your distributor. I've seen several of these that are pretty sloppy by now.

I think he said the Mallory setup was going to cost him over $150 and he still had an old worn distributor and he would still need to find a new vacuum advance.

Jerry and I talked about this around Christmas and recently (above). We've agreed setting up the distributor to run on an electronic scheme could be done in one of about 3 different ways inexpensively and easily. Some would preserve the old look. We just haven't had the time to pour into the project yet.

For what it’s worth, I don’t even know if Mallory makes the optical trigger conversion unit for a GM 6 cyl. They might, I haven’t searched all that hard.

I do know they make them for factory GM and Ford points-style distributors. Just curious if the concept was a good one and any real-world experience with the reliability.

I have modified two distributors as per Jon's instructions using all GM pieces. The engine starts every time, it allows me to run a wider gap on the plugs, burns hotter and more complete. Most people don't notice the difference in the distributor. I won't be going back to points.

I believe Jon has found the fault with the Pertronix unit, the question is can it be corrected?

Many years ago Mallory replaced their very effective (and difficult to tune) dual point setup with something called a "Unilite" system. It used an optical trigger (infra-red, I believe) instead of points, and some sort of adjustable centrifugal advance. No vacuum. I don't recall it being very popular with the round track crowd, and I've never been one to waste much time on drag racing. At the time, I was modifying "stock-appearing" HEI units for small block Chevy V8s to let me turn my engines 1K RPM or more faster than my competition, and hiding the mods from the tech inspectors in the "street stock" class at the local round track. Once my driver made it to the front of the pack, the only thing the race was going to decide was who was going to run second!
Jerry