Exploring The Differences Between GM HEI & (Ford) Motorcraft/DuraSpark Ignitions








IMPORTANT ADDENDUM!
Many of the HEI Clone manufacturers have been using distributor gears of 'Forign' origin,
Poorly made raw cast iron gears from Mexico and Hardened Steel Gears from Spain


THESE GEARS WILL EAT UP YOUR CAM SHAFT OR CAM GEAR IF YOU USE THEM ON YOUR STOCK AMC ENGINE PARTS!

Here are some pictures of the offending gear on an aftermarket distributor from '4WD.com'
4WD.com p/n DA13,
Invoice p/n WP8919

As you will see in the pictures, there was noting wrong with the distributor or dive gear that came out of the engine.
The user simply believed the advertisements and purchased one of the 4WD.com distributors believing that it would give him more power and fuel economy.
All the while not realizing the hardened steel distributor gear was going to eat away his Ductile Iron cam gear...


Notice there is NOTHING wrong with the DUCTILE IRON distributor gear, and the factory ignition was working fine with the cam gear at this point.


As you can plainly see, the factory cam shaft gear (RIGHT) was eaten away by the hardened steel gear of the new distributor.
It should look like the new gear to the LEFT...

This is a shot of the new distributor from 4WD.com next to the ruined gear,
Notice the little serrations in the edge of the distributor gear teeth?
Considering this was hardened steel gear on a factory soft Ductile Iron gear, those HARDENED, SERRATED STEEL TEETH might as well have been the cutting tool in a milling machine!


Here is a link to the forum thread covering this catastrophe, and I will post others as they are made available to me.

Jeep Forum Thread Link, Click Here.




Here is another case of a bad HEI clone destroying an engine.
In this case, it's the 'Too Much Advance' I warn about in the comparison below.

Quote From Jeeps Unlimited Forum User, "Hill, Bill E",
"I have a HEI from 4WDH. The vacuum advance diaphram was to tight, one of the mechanical advance springs as stretched (visably), and the coil in the cap sucked compared to the OEM GM stuff from the 80's.
Ended up with detonation when fully loaded and towing the adventure trailer, kind of like driving it with the timing advanced to much.
Cost me a valve and piston, and the time to tear it down and fix it.

Fixed the dizzy with parts from 2 other GM OEM HEI dizzy's I had, replaced the coil, vacuum pot, mechanical springs and electrical components.

I bought the 4WDH one becuase everything I'd read had been good, I may have gotten a bum dizzy, not sure.
The $200 I saved ended up costing me that much in parts/machine shop fee's, not to mention my labor.
Worst part was, I was on the way to Moab, when the valve burnt. Still went to Moab, and wheeled a rental, but didn't get to wheel my CJ there.
The best. By going the 'cheap' route, ($150) it cost me my trip to Moab, wheeling so far this year, and this:"


Used with permission, Picture credit, Hill, Bill E.


Used with permission, Picture credit, Hill, Bill E.

Quote, Hill, Bill E,
"And of course all the associated costs, gaskets, machine shop, time...
Yep, I sure cut a fat hog by saving $200 on a HEI dizzy."


This is typical of a HEI distributor in an AMC engine. The AMC engine just wasn't designed to handle the advance curve of the HEI distributor,
And when you factor in the aftermarket clones complete lack of regard for quality parts (mostly import crap), it's easy to see why AMC engines suffer catastrophic failures when the HEI clones are used!




NOW, Back to the HEI comparison and Review!
For you 258 I-6 guys (and to a lesser extent the V-8 guys) about which ignition system is the 'Best'.
'Best' is a relative term, so lets break this down logically...

In this case we are going to go over the two ignition systems, explore the strengths and faults of each, and see if there is any particular application where one would be much better than the other.
With more than 30 years in racing and Hot Rodding, I am INTIMATELY familiar with all the factory and most of the offerings from the aftermarket. I know what works, and what doesn't, where money is well spent and where it's wasted.
I'll share that experience with you here...




Let's start with application.
If you have a '78 to '90 Jeep
, you have a Motorcraft distributor and DuraSpark Ignition module.(Ford)
This is an easily upgradeable system, easy to work on, easy to get top quality parts for, and easy to tune.
There is no reason in the world to replace this distributor, it's easily tunable, upgradeable with factory parts, reliable as an anvil and will accept upgrades to it's module, coil and nearly everything else!
See here for details,
TeamRush Upgrade Pages.




If you have a '74 to '77 Jeep, you probably have the Prestolite Distributor & Ignition module.
Some full size Jeeps were still using points in '74. If so, see points section below.
It's easy to tell, gold color ignition module on the passenger side fender, distributor has a plastic vacuum advance housing, and if you remove the cap and rotor, the reluctor looks like a spider squatting on top of the distributor internals.
Not wanting to put too fine a point on it, but this was the most unreliable of the electronic 'Solid State' ignitions.
The distributor design was horrible, it used plastic parts, like the vacuum advance, that decompose with exposure to heat and gasoline fumes, it used a true Hall effect trigger, so there are no factory and to my understanding, no aftermarket modules that will work with it.
The factory module is a poor design and prone to failure (as any of you that have owned them already know!), and it's performance switching the coil is at the bottom of my rating list.
In my opinion, it was an utter failure.



If you have a '70 to '74 (and some '74 full sizes) with a points ignition, you have the Delco Remy version of the points distributor.
Great little unit, but only upgradeable through some aftermarket parts.
If you have a V-8, any parts made for a Cheorlet V-8 with points ignition will work with it.
This includes, upgraded caps & rotor (sorely needed!), electronic ignition triggers, and the stock points are compatable with modules like the MSD 6 series with no modifications to the distributor.
See this article for a $25 electronic trigger upgrade using off the shelf parts and a round file.
CJ-5 Ignition Upgrade



As for the debate between the GM HEI swap in, and the Motorcraft/DuraSpark ignition...
For '78 to '90 Jeeps,
You DO NOT have to remove the distributor if you use your existing Motorcraft/DuraSpark Distributor!
This is a big plus if you are 'Shade Tree Mechanic' that likes to do his own tune ups.
The 'TeamRush' is a very valuable upgrade, designed to fit directly onto your current distributor, since Ford continued to upgrade the DuraSpark ignition through out is useful life, we can benifit from those updated parts.
The basic upgrade is all 'Consumable' or 'Tune Up' parts, but must go on together.
There are more upgrades later, but these first 4 components must go on at the same time.
They are, Distributor Cap Base, Distributor Cap, Rotor, Plugwires.
This will bring your ignition up to date so you can start with power upgrades, and couldn't be simplier.



For '74 to '77 Jeep CJ, '75 to '77 Jeep FSJ, You don't have any real options for that ignition. Sad but true.
What I do recomend is swtiching out that Prestolite ignition.
You have two basic options,
A. I-6 guys, Pull out the Prestolite ignition, and replace it with a Motorcraft distributor for a '78 or '79 I-6 Jeep engine
This is a direct drop in for this application.
With that very solidly designed and built distributor as a center piece, you can use the 'TeamRush' Cap, Rotor, Plug wire upgrade, and about any igniton module or ignition coil you want to.
You will have to aquire the distributor (new or reman), distributor gasket, cap, rotor, plug wires, ignition module, ignition coil and do some simple wiring.

B. A second, less recomended ignition (but still an upgrade from the Prestolite) is a GM HEI distributor from a '76 or '77 250 CID I-6 Blazer.
The GM HEI has a long list problems, but is still more dependable than the Prestolite.
For this application, you will need to aquire the distributor (new or reman), distributor gasket, cap, rotor, ignition coil, module, module heat transfer paste, drive gear, ect.. In the case of replacing the Prestolite, after you assemble the parts, the wiring is a one wire hookup. Personally, I'd add a dedicated ground to this unit also.
Bear In Mind... this is NOT a direct drop in, and this distributor, though it will work, was never intended for this application.
Also... the GM HEI distributor I recomend IS NOT THE COIL IN CAP VERSION!
I'm trying to save you some problems by giving you the version that has a remote ignition coil. GM removed the coil from the cap for a reason, and I think it's a good idea also.



Now I'll explore the differences between the GM HEI and the Ford Motorcraft/DuraSpark components.

1. Location & Attitude Of Distributor.
GM intended for it's coil in cap arrangment to to sit stright up, the same as the the other GM distributors had been designed to do. This is a throw back to the wildly successful poplularity of the Chevrolet V-8 engine design and the fact the distributor stood directly vertical to the axes of the crank & cam shafts.
When it was adapted to the I-6 engines, it was placed at an angle to the engine block.
This put the full weight of the E-core ignition coil pulling down on the cap & stem of the distributor, and also put excess pressure on the cam drive gears when loaded with gravitional forces, but inertial forces from rough driving were brutil on the mounting/mating connections and moving parts.
The coil was removed from the cap, and the stem shortened in an attempt to reduce the inertial loading.
It would be wise to do the same if you intend to use this distirbutor at an angle in an AMC engine.

Ford and Chrysler never had this problem with their distributors, both having kept the modue & coil weight off of the distributor head, and using smaller base circle on the head of the distirbutor, the stem of the distributor was much shorter, reducing the leverage the head weight had on the stem, drive shaft & gears.



2. Plug Wires.
The GM HEI had only one significant upgrade change since it's introduction in 1972, Plug Wires.
GM started with an updated plugwire design, the first real upgrade since WWII.
The terminals were inovative since they seemed to have a spark plug terminal on both ends.
This is the design most of us use to this day.

Ford Followed suit in 1975 with the release of it's upgraded version of the tried and true Motorcraft distributor wired to it's DuraSpark module.
Other advances included a plug wire for the time that was low resistance, low impeadance, and used a high heat silcone insulation.

Since most of us use aftermarket wires, this is a moot point.
A premium set of aftermarket will cost $50 to $75, but are well worth the price for the years of reliable service they will give.
I would feel remis if I didn't comment on 'Discount Store' plug wires...
These are a little cheaper, but you get what you pay for, and these wires are NOT the way to go! (with the possible exception of 'Autolite' brand name wires).
Each and every time a customer brings his own 'Discount' wires in, we test them before installing them, and virtually every single set fail for either resistance, opens in the conductor, EM noise, ect.



3. Ignition Coil Design.
The GM HEI Remote coils, both the two wire and the 4 connector are about equil to the Ford E-core in secondary (high voltage current) output.
There are no significant variations in design, winding ratios, or current requirments between manufacturers. This means the remote mounted E-core coils are virtually interchangable, except for connector configurations.

The GM HEI 'In Cap' coil is significanly flawed.
The winding ratio, the winding conductor size, insulation between winding sets, internal insulation for the secondary current, and the secondary output terminal are all substandard when compaired with the remote mounted coils.
This transformer coil was designed to blast out high voltage with no regurard to controling that discharge, or to having amprage or duration to that discharge. (duration and amprage are both important elements to useable spark energy)
One must rememeber the high voltage output of the coil in cap arrangment is virtually unsealable, and will leak to ground both inside and outside the cap it's mounted in.

The Jeep Factory version of the (Ford) Motorcraft ignition used a oil filled canister type coil.
Fairly reliable, but can be problematic to mount since the oil filled 'Canister' or 'Volcano' coil has to be mounted vertically to cool correctly.

A common upgrade is to directly replace this oil filled canister coil with a later model E-core style coil. Ford used the E-core design with the DuraSpark ignition module on export vehicle for years, so this is a direct drop in replacment.
This will give you modest gains in secondary voltage, but will give you respecteable gains in amprage and duration of spark energy. A worth while investment of time and money for the drivability gains and economy increases this upgrade will bring with it.



4. Distributor Cap.
The GM HEI factory distributor cap is an exercise in design compromize.
This cap design has so many flaws I don't know where to start...
I'll start here...
For those of you that don't have a degree in electrical engineering,
The #1 rule of electrical flow is, The charge will always seek the easiest way to ground and that isn't always the way you intended for it to go...(ever get zapped by a plug wire! that wasn't the way you intended!)

For a spark to jump from one point to another, the gap has to ionize, then polarize, then electrons can jump through this ionize corrodor of air.
The more air between terminals,... The harder it is to ionize the air in the gap,... And the harder it is for the spark to jump.
This is why wide spaces between terminals is a good idea, the more air gap between terminals the better chance your spark energy will go to the spark plug terminal it was intended for...
The secondary discharge 'spark energy', will find the easiest way to ground, even though it might not be the closest terminal simply because the ionized air makes a trail more inviting that the intended terminal.

A. The cap has a center electrode. In the remote coil versions, this electrode is fixed, and that is a good thing.
On the coil in cap version, this center electrode is connected to the coil by a very fine steel spring.
The coil high voltage soon distroys the conductive elements of that spring, and the spark has to jump a highly resistive gap to a graphite center button in the cap.
The extra resistance here often prompts the coil to discharge internally, or discharge outside the cap. Both of which are distrucive.
That discharge over a gap creates ionized air and pressure, and that pressure will blow the insulating gasket out in the coil chamber of the cap.
Soon, the coil chamber will be full of ionized air, and the secondary discharge will escape to the outside of the cap.
I've seen center terminals in such bad shape that the secondary discharge was actually comming out of the coil compartment and grounding to the distributor housing outside and over the cap!... The sad part is this is not uncommon!

B. The cap is non-vented. No vent means the ionized air in the cap builds up.
With the entire cap and distributor head filled with ionized air, the spark energy has free reign to jump where ever...

C. The Aluminum terminals in the factory and most aftermarket caps mean resistance.
Aluminum isn't a very good conductor, so with the ionized air filling the cap it may be easier for the secondary discharge to find ground to another terminal, to ground inside the distributor, or to parts of the ignition module or pick up coil.
This is VERY common!
If you use a GM HEI, I recommend you use a premium cap with BRASS terminals.
(Not one with brass washed aluminum terminals, very common)

D. In an attempt to cut costs, many HEI distributor caps, both factory and aftermarket, were colored with carbon black.
Carbon is the by product of combustion (soot), and is CONDUCTIVE!
So now you have your spark energy in a cap full of ionized air, and jumping around on carbon tracks built into the cap!
Most of the aftermarket import caps are made with carbon black to this day!
I recommend you buy a 'Colored' cap, and not a black one.

E. Terminals in most HEI caps are aluminum.
Aluminum is much cheaper than copper or brass, so, unfortuanatly, it's widly used.
The aluminum terminals in the HEI cap 'Expanded Inserts', meaning the cap was cast, then the aluminum terminals were inserted and expanded like 'Pop' rivets
This means the terminals are not sealed to the cap marterial and they move around with both manual movment (force of plug wires moving them around) or thermal expansion & contraction, the terminals become loose and leak.
This causes the terminals to be both misaligned, and have a pocket of non ionized air around them.
The resistance in the aluminum, combined with the carbon tracking in the cap, a cap full of ionized air, and non ionized air around the terminals, you have a recipe for not getting spark to the correct plug...
I recommend you buy a cap with brass terminals that are cast in, not 'Expanded Inserts' made of aluminum that are brass washed.
One very quick way to tell if the terminals are cast in or expanded, look closely at the top of the terminal, is it a nice machined piece of brass, or does it look like it was pressure form molded.
Another way is to look inside the cap at the terminals. If they are flat pieces that look the the head of an inverter 'T', they are expanded. The expanded terminals need the 'T' head to keep them from turning during the 'Rivet' process. If they are round bars of brass that have had half of it's diamenter machined away for contact surface, it's cast in. Cast brass components are already in the mold when the plastic is injected, so they can be round (with a terminal notch inside).

A premium Motorcraft Distributor upgrade cap doesn't have any of the problems.
The better premium Ford style caps and brass terminals, venting, a riged internal surface helps isolate stright lines of ionization, the cap material is true dielectric and the center electrode is fixed with adirect connection.


5. Rotor.
The GM HEI rotor has a virety of problems.
They are too thin for the amount of coil current they are trying to handle.
Blow thorugh is pretty common.
The design of the advance head and fly weights puts a dead ground right under the rotor.
Grounding around, or blowing thorugh the rotors is so common you may actually find fly weights welded to the head or thier pins, and you will find 'Red Dust' everywhere in the cap and distributor head.
'Red Dust' is the result of high temp (from high voltage) discharges into the steel of the distributor shaft, advance head and centrifugal weights.
When a high temp discharge hits steel, it burns the carbon and most of the alloy materials out of the iron, and the 'Red Dust' is what is left, Iron Oxide, or mostly pure iron rust.
Welders can verify this, welding bruns the carbon and alloy materials out of the steel, and mostly iron is left. Iron rusts in a deep red color, where steel alloys rust to a light brown.
Anyway, the red dust is still conductive, so anywhere it settles becomes a conductor.
Combine the iron particles with ionized air, poor quality terminals conductors, carbon tracks in the cap, and you have a distributor that doesn't 'Distribute' like it's suppsed to...
I recomend one of the much thicker and wider aftermarket rotors that are made of a true dielectric plastic or fiber resin.

Ford solved this problem by distance. They moved the rotor up away from the distributor shaft.
In a vented cap, with a properly designed centrifugal advance system away from the secondary discharges, and with the rotor conductor much farther away from the available grounds, the rotor delivery system becomes much more reliable.
The Ford style rotor also has a 'Fin' that helps stir up the ionized air in the cap, keeping it from polarizing, and preventing an internal discharge.



6. Centrifugal Advance.
Although this is already partally covered, the centrifugal advance assembly is on the top of the GM HEI distributor shaft, and located right under the rotor...
This arrangment has long been touted by 'Shade Tree Mechinics' as optimum for tuning the weights and springs, but it also puts the weight at the top of the shaft, a long way up above the last shaft support bearing.
And it makes a seriously attractive ground for the secondary discharges in the cap.

Although the GM HEI is often touted as the 'Easiest' Centrifugal advance to tune, the truth is you only curve or recurve the distibutor only once or twice in it's lifetime, so 60 seconds extra 'work' to do the recurve isn't really an issue.

There are no recomendations here. Fixing the problems of the centrifugal advance's mechanical defects include simply replacing the head and weights with aftermarket parts, as there is no factory support or parts available for this part of the distributor.



7. Module Location.
A. The GM HEI chose to locate the control module INSIDE the distributor body!
This makes it vounrable to high voltage secondary discharges that are constantly occuring inside the cap
The wiring for the module is under constant bombardment from the high voltage discharges also.

B. The GM HEI module has a problem with switch ramping when it switches the Ignition coil on and off.
The faster, or 'More Square' you can make the closing of the ignition coil circuit, the more time the coil has to saturate.
The 'Ramp Effect' (when opening & closing is viewed on an ocilliscope) or slow closing of the transistor circuit is one reason the 'Coil In Cap' was designed to deliver sheer voltage and disreguard spark energy essentials like amprage and duration.
With massive voltage discharges (which caused problems in their own right) the coil output guarinteed at least one discharge, be it at the plugs or not!

With the slow opening of the circuit, a long ramp is created on an ocilliscope also.
Slow opening leads to a gradual decrease of the magnetic field in the ignition coil, instead of a quick and total collapse we are trying to acheave.
The slow decrease means slow movment of the magnetic field through the secondary windings, and reduced 'Useable Spark Energies' on the output side.
For best performace, the circuit should open instantly so the magnetic field will collapse totally and as rapidly as possible, but here on planet earth, there is no such thing as opening an electrical connection 'Instantly'...

C. The next problem addressed is the heat generated by the GM HEI module.
This little module doesn't have a built in heat sink, and REQUIRES a heat sink be attached.
GM decided to bolt it to the distributor housing, which isn't all bad. Aluminum is a good conductor of heat, and there is a lot of aluminum in the distributor head to transfer and regulate the heat produced by the module.
The problem starts when the proper heat sink/ thermal jointing compound isn't used.
Most guys get an aftermarket, forign made, replacment module that comes with dielectric grease instead of heat transfer paste.
The guys that did nothing inside a salvaged distributor often don't know that heat sink paste dries out, falls away, and is ineffective when it's dried or diluted.
The GM service manual actually recomends cleaning and reapply of paste every year.
(In fact most guys can't identify the internal parts of the distributor, so proper knowledge is scarce!)

D. Grounding Of The Module should be address by the end user.
GM HEI, like all factory ignitions, relies on proper grounding of the engine to ground the distributor, and in turn ground the ignition module.
The GM HEI is no exception, and has 'Grounding Issues'.
The ground for the entire primary side of the ignition is through one module mounting screw.
The module, and screw, are often rusty, engines are often poorly grounded, the working joint between the distributor is often caked with non-conducting 'laquor' type 'crud' from old, dried engine oil, and the moving connection between the distributor shaft/gears is like any moving connection and can not be relied on.

Recomendation here is to use a over length BRASS screw to mount the module on the grounding end. Use a star washer under the bolt to module connection to maintain connection during thermal expansion and contraction cycles.
Use a dedicated ground wire on the excess end of the brass screw that exits the distributor housing. This will ensure ground to the primary side of the ignition, and is a quick, easy, cheap and reliable upgrade.



8. Ignition 'Condenser'.
'Condenser' is a misnomer, the device is actually an electrical Capacator.
The capacator is located in the GM HEI not at the ignition coil where it would do the most good, but at the ignition module!
It took me months to figure this out!
Turns out the module power connection is struck so many times by high secondary voltage, the Capacator was located close to the assulted terminal to keep the module alive!
Anyone that has driven an older GM vehicle knows the ignition system comes through on the radio loud and clear!
Some designs tried to use a 'Notch' in the fire wall to cut down on ignition noise, others used a metal shield over the distributor and plug wires to keep the noise to a minium.
Moving the condenser to the ignition coil would have done wonders, but every time that was tried, the module took a beating!
(The ultimate quite engine, non-running!)

If you browse my diagrams, designs and pictures, you will notice I NEVER use an HEI module without a Capacator!
Locating the capacator at the module power terminal adds to the 'Ramp Effect', but it's required with a GM HEI, and should NEVER be excluded.

In the interest of fairness, if you use a GM style HEI module externally, away from the coil and plug wires, you still need a capacator to keep the switching transistor from distroying it's self.... If it weren't for that, you could move the capacator to the igniton coil like every other ignition...

You should also notice the capacator on the Ford ignition is at the ignition coil if it's used at all. The grounded case of the module keeps much of the nose out of the radio, and since the DuraSpark module is externally located, the threat of secondary discharge to it's power supply is 0 (zero).



9. Design Of Distributor Body.
The GM HEI distributor body is 'T' shaped, and reaches the full diamteter of the cap immedately at the top of the housing.
This is just fine if you are mounting the GM HEI distributor stright up out of a V-8 engine, but presents problems with an angled install, and is a real problem with an I-6 install where it has to stick at an angle out of the side of the block...
The larger head diamenter means the stem of the body has to be longer so the head can clear the block, and longer means more leverage for the weight of the completed distributor on that stem.
Hard on internal bearings, hard on gear placements and interactions, hard on everything.

The reduced base circle diameter of the Motorcraft distributor allows for a much shorter stem on the body, and with the tapered cap adaptor, you can still have a full size distributor cap.
The design of the Motor craft distributor also has load much closer to the bushings/bearings, keeps the weight out of and off of the extended part of the shaft, and adds housing support above the top shaft bushing/bearing.



10. Tunability.
A.Tuning of the GM style HEI centrifugal advance timing is fairly stright forward, remove the cap and rotor, change weights or weight springs.

With practice, you can access the weights and springs in a Motorcraft distributor in about 60 seconds, and they adjust EXACTLY the same way.

B.You CAN NOT adjust the total amount of advance or retard in the centrifugal system of a factory GM HEI.
There is no provision for changing the total centrifugal timing.
You will have to remove the distributor, dissasemble the distributor, and use an aftermarket kit or grind, drill and relocat parts to change the totals of the centrifugal system.

Motorcraft distributors all have at least one centrifugal change built into them, and it can be accessed in 60 seconds with out removing the distriubutor.
This total tuning change can be custom set with a file or small grinder by the user with out removing the distributor from the vehicle.

C.In a factory GM HEI there is no tuning of the vacuum advance. Peroid.
GM made NO provision for either tuning or limiting the vacuum advance from the factory.

Most Motorcraft distributors have a tunable vacuum advance from the factory.
To know if you already have one, look at the vacuum hose nipple, then look at the canister just behind it... IF you have flats that resemble a 'Nut', then the canister is tunable with an 'Allen' wrench through the vacuum nipple.

So the next time someone tells you a Motorcraft distributor isn't tunable, just smile and say, "This is America, and people are allowed to speek on subjects they have no knowledge of."



11. Gear Engaugment.
This is one of the things that bothers me the most!
To do a GM style HEI swap to an AMC I-6 Engine, you have to swap the factory Chevrolet gear for an AMC V-8 Gear.
Since the shaft diameter is with in 0.005" to 0.009", the shaft fit isn't that large of an issue.
It's the location of the distributor drive gear on the cam shaft that bothers me!
Although the cam will engauge enough of the teeth of the distributor gear to turn it, the gear is seriously misaligned with the center line of the cam!
You are actually only engauging the very edges of the teeth of the V-8 gear!



The gear on the left is the stock AMC I-6 Gear, and the gear on the right is the AMC V-8 gear you have to use to get this 'Swap' to work. As you can see, both use the same roll pin to keep them in place, but look at the difference in the gear locations!

I wish I had an easy sloution for this, but I don't. No one makes the correct gear for this application that I know of, so for me this is the largest nail in the coffin of this very popular project.


NOW You Have An Engineers Opinion Of This Very Popular GM HEI Distributor Swap.
I hesitate to call it an 'Upgrade' even when used in place of the Prestolite system or when replacing breaker points...
Anyway, here are the facts, make up your own mind and decide for your self.