Distributor question for Michael

P

pineneedle

Member
Michael,

several months ago we corresponded about my distributor. To refresh your memory, it is a prestolite electronic off a 1978 304. It has two wires that lead to some electronic stuff under the main plate. At the time we last talked, you said to take it apart and to assess the wear. Well, I got sidetracked into axles and other stuff, but I am now back to the distributor. It has .042 end play. The bushings seem very tight, the bottom having no runout at all. The top has about .003 measured at the end of the shaft. What do you think?

There is an eight bladed thingy on the top end of the shaft. I presume that this is an electronic trigger of some sort. Since I am going to go with a pertronix igniter, I presume that I take this piece off. Is that correct? Is it just a press on fit to be pulled off, or is there some special mo-jo necessary?

As always, thanks for your help.

Pineneedle
 
Hey john!

That "eight bladed thingy" is called the reluctor. Don't attempt to remove it, it's made onto the mechanical advance component. Actually, prestolite refers to that item as the "trigger wheel" and it's companion pickup as the "sensor".

The magnet ring that is included in the pertronix conversion kit will push down over the reluctor and is held in place by friction.

The prestolite electronic distributor has it's control module under the pickup plate, making it a self-contained system. That is unlike the other electronic distributor variation IH used which we refer to as a "gold box" system. That unit has it's control unit mounted on the engine compartment bulkhead. Both types of electronic distributors use the same coil however.

There are many different pertronix electronic pickups (triggers) depending upon which distributor it's designed to install in. Likewise, there are many variations of how that trigger is mounted to it's adapter plate. Those are not a "fitzall" solution!

Likewise, the various types of distributors use different forms of magnet wheels also. Some push down over the point cam, some push down over the reluctor, some mount with two screws under the rotor (as onna delco), etc.

This why it's critical that the correct pertronix conversion be selected for the exact distributor you are working with.

When you install the pertronix module, you must set the "air gap" using the included piece of acrylic thickness gauge. That is how the dwell for this unit is set. Once it's done, you don't mess with that anymore. The same process is used on the original prestolite pickup system.

The endplay spec for that unit is 0.035">0.040". So your end play of 0.042" is "ok" in my book. But...reducing the end play can really "crisp up" ignition timing across the rpm spectrum. In order to do that, you will have to punch out the roll pin in the drive gear and remove the gear from the shaft. The gear is a press-fit but not super tight.

I can send you the shim you need to tighten up the endplay if you wanna mess with that, I keep a large assortment of those shims for all IH-app distributors. Is so, just post here and I'll stick one in an envelope, I have yore contact info in the dbase! Your choice.

Can you post the actual IH p/n and the prestolite p/n on the data plate??? I wanna see "which" distributor you have, there are ten different part number units just for the sv engine app! Quite a range of advance curves spread over the different versions.

Your distributor should have three wires coming out of it's pigtail. The white wire goes to the "decel" switch which you don't have and don't need on your rig! Just leave it disconnected from anything or clip it off. The pertronix conversion has it's own harness made in, simply connect it per the instructions.
 
Why the conversion to the pertrionix? Has your prestolite kicked it?

The pertronix is a step backwards, the prestolite can sink the current from a 1.5ohm coil being supplied b(+) and won't fry if the key is left on.

Neither pertronix can sink that much current, all the ones I have seen require a minimum of 3.0ohms primary resistance, meaning that it can only sink half the amperage safely.

The pertronix I will fry if the key is left on w/o the vehicle running they fixed this with the pertronix II.

To clear things up the pertronix for the prestolite replaces the entire advance plate and includes a trigger that slips over the existing reluctor which is pressed on the shaft.

To install the pertronix in the presto electronic you remove the entire "breaker" plate and wiring and install the new unit w/its wiring harness and dist pass through grommet.

Not all presotlite electronic distributors have the 3rd white wire, some have only the red and brown wires.
 
Ihc v8 cylinder distributor apps use any coil with a primary resistance of 1.4>1.8 ohms to give excellent coil saturation (current draw) with either breaker point systems or a pertronix conversion. The "nominal" primary resistance spec is normally shown as "1.5 ohms".

I-4 (ihc) and I-6 (ihc or rambler) cylinder apps using a pertronix conversion like to see a nominal 3.0 ohm primary resistance coil. Same is true for a breaker point app.

This ain't rocket science, even pertronix gets it right in their own specs:

flame-thrower ignition coil application chart

In their specs, the max terminal "voltage available" spec is meaningless for this discussion, that's simply a factor of "turn ratio" in those conventional coils. No different internally than similar offerings from mallory, crane, accel, msd, etc.

Using a "low" or "ultra low" primary resistance coil with either pertronix module will bake it quickly. However...those type coils can be used with a pertronix if...a cd ignition box is used in the system such as any msd/crane/mallory "6 series" unit. That is because the pertronix serves only as a trigger for the cd box and is not loaded with full primary current at any time.

A prestolite electronic unit is a fine distributor/ignition system. But the "cost" of replacing the guts if they take a dump is far greater than simply converting to a pertronix trigger system. And either system is a simple inductive ignition system, same as an hei or it's clones. A definite "upgrade" is implementing a "6 series" cd box and using the pertronix to trigger it. Then any coil can be used (within reason).

All this "stuff" is being discussed in this thread (pertronix trigger/mallory hyfire 6/msd low resistance coil), the msd coil seen in the last post has a primary resistance of an actual 0.55 ohms, though the msd "spec" sez it's 0.42ohms.

Let's see...breaker points "burn up"/over heat if ya leave the ignition switch "on", a crane optical conversion burns up if ya leave the switch on, a "gold box" system will overheat if ya leave the ignition switch on, a crane xri lobe sensor conversion (for a delco) will fry if ya leave the switch on...the solution to that? Don't leave the switch on without the engine running! If ya have to "trouble shoot" something with the switch on, then disconnect the "red" wire from the pertronix to coil + terminal.
 
Michael and eric,

thanks for the replies. Michael, I have searched everywhere I can think of on that sumbich, and I cannot find any numbers. The only numers are a raised "1" that occurs in two different places. So, I don't know what to tell you about which electronic prestolite I have. As for the "spacer" to tighten up the end play, yes, I would really appreciate it if you could send me one. But can you do this without a part number off the unit?

Eric, you are asking the wrong guy. I don't know enough about these things to give you a reason for my choice of the pertronix other than that I have one in another application and love it. As for this distributor, I don't know if it is functional or not. I got the motor from a local I-h guy who had it on an engine stand in a storage unit. I have no knowledge about its history, whether it was running when pulled, etc. As michael knows, I have rebuilt the motor, but have not gotten to the stage of firing it up yet.

Pineneedle
 
"correct" distributor shaft shim ain't no problema from my end john!

Use your feeler gauges and double check the "end play" between the top of the gear and the end of the aluminum shaft housing with the distributor on the bench. Post that one more time for verification.

Then I'll know what shim (May be a shim pack) to send you. Based upon your previous statement regarding 0.042" end play, then I'll send ya a single 0.030" shim, that gives ya a nominal 0.012" end play when installed with is perfect!

By the way...all the IH app distributors use a nominal 0.500" shaft (actually 0.485"). In the parts bizz...we call that a 1/2" distributor and ya sometimes found 'em referred to that way in parts catalogs and such.

It's the replacement drive gears for IH apps that are a problem...the common sources for drive gears don't do IH items anymore. And all the custom distributor folks are buying up all the cores they can find to rob gears from and scrap the rest of the unit. Just recently we located a "possible" source of gears, I've even bought two new gears through the local IH dealer but can't get any more unless someone in some dealership still has a few on the shelf.

It's the same deal as for the vacuum canisters for the IH/Holley distributors, can't find 'em new at all other than maybe nos somewhere, going price for a new one now is $85>$100. But we can have ng units "rebuilt" now.

If you have an "old time" auto electric shop/garage anywhere near by that May still have a distributor machine and someone who knows how to run it, then your electronic prestolite unit can be tested on that machine using a procedure outlined in the service manual, an external battery is used for doing that. I can send ya the process if ya don't have access to that info. If the prestolite is indeed useable, then you could run it for now. If it takes a dump, then p-tron it at that point. All the diagnostic info in IH service publications was based upon throwing the distributor in the machine and running it up. Final base timing was done after re-install in the motor of course!
 
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pineneedle said:
I have searched everywhere I can think of on that sumbich, and I cannot find any numbers.

I don't know if it is functional or not. I got the motor from a local I-h guy who had it on an engine stand in a storage unit. I have no knowledge about its history, whether it was running when pulled, etc. As michael knows, I have rebuilt the motor, but have not gotten to the stage of firing it up yet.

Pineneedle
Click to expand...

The numbers on a prestolite are on a "house" shaped tag under one of the screws that holds the plate assembly in, so unfortunately they often go missing, particularly if the unit has been reman'ed in the past.

The prestolite unit is extremely reliable, I can understand replacing failed unit, but to toss it untested why? Only takes a couple of seconds to test. Disconnect the coil (-) on your other rig position the dist end of the coil where you can check for spark. Then connect the red to coil (+) and brown coil (-) wires from the prestolite, ground the dist body, turn on key give it a spin by hand, and check for spark at the coil wire.

If it is bad then yes the pertronix is a cost effective option since a new prestolite module can run in excess of $300 depending on where you shop. My bet is it works, probably has quite a few years left in it, and it won't fry if you happen to leave the key in the on position for more than 30 sec.
 
Michael, sorry for taking so long to respond to your question. Life gets complicated. Anyway, I went back and measured very carefully with a feeler gauge. I get a gap of .044. There are four shims on the shaft already, two between the gear and the housing, and two on top between the "tub" and the shoulder of the shaft. I call these shims. They are like washers with lips that nest into each other and into the hole the shaft goes into. I presume that they are original; I suspect that they function like thrust washers. Anway, that is what I have. If you can send me the right size shim to snug it up, I will be happy to compensate you whatever it is worth. Thanks,

pineneedle
 
Ok john! This is a hobbyproject and we ain't tryin' to make a ride so we can get to work on time! Since neither of us have that "work problem" to be concerned with...everything izza hobby!

The upper shims are thrust elements peculiar to the prestolite. Many of the aftermarket distributors (most notably msd) use shims similar to those also. But I don't think the "cupping" is an original deal, that comes from excessive end play developing over time. As endplay increases, then ignition timing throughout the rpm range becomes somewhat erratic resulting in engine performance deterioration. We're gonna bring yours back tighter than spec!

You will keep those nesting thrust washers shims in place just as ya found them. When you reassemble just put a thin film of lube on the faces of all moving/rubbing points inside the distributor and the advance mechanism. I use an anti-seize compound for that but a very fine film of that moly-filled (black nasty stuff) "hi-temp" wheel bearing grease sometimes used in disc brake hub apps works just as well.

I use the same stuff applied to the upper and lower bushing and on the shaft itself during reassembly. Ya can't imagine how nice a fresh distributor actually feels when you rotate it!

I'll send you today a 0.030" shim to add to the existing shim pack above the drive gear today. Once you are ready to push the gear back onto the shaft, then simply use the same "lube" treatment. So ya should end up with around 0.012>0.014" endplay when all is ready to drop in place.

Before stabbing the distributor, turn it upside down and squirt motor oil through the oil port in the lower body while ya rotate to distribute. That hole is how the shaft and bushings lube when the motor is spinnin'.

I'll also send ya an "o" ring to use under the distributor instead of the oem-type gasket for sealing.

No cost at all...when I figgr ya owe me $500 over the next 20 years, then we'll settle up! Then our respective "estates" can deal with it!
 
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