elec. prestolite compatibity

7

78IH

Member
I bought a reman distributor from napa, elec prestolite, napa pn 48 44824. For a 76 SLL, 304, 4spd. I am wondering how it compares to the 484778c91 4002b 417 on my 78 SLL, 345, 727? Would the napa one work on my 345? Because the one that came off my 345 probably needs to be replaced. Im scraping the body and chassis of the 76 eventually. So it would be real convienient if the napa distributor was a correct match for my 345, but I doubt it. There is no id tag, and I cant feel stamped #s, 48 44824 is off the box. Napa doesnt sell distributors online, but im going there soon, so ill check what #s it replaces.
 
It replaced 496004c91 idn 4002r 7s9. Isn't there a IH pn book? Would that help me? Would it tell me wheather or not the 2 IH pn's are compatable? Going to napa in a few days, ill see there.
 
78ih said:
it replaced 496004c91 idn 4002r 7s9. Isn't there a IH pn book? Would that help me? Would it tell me whether or not the 2 IH pn's are compatible? Going to napa in a few days, ill see there.
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I responded to this in your other thread...I'll do the research tonite.

Ya can't trust any napa or any other aftermarket line for specs such as you need. They simply don't deal in that kind of stuff. The big picture for distributors is in the cts 2300 service manual, that is a compilation of many vehicle platforms and manual segments. An extensive table of all distributor and carb specs is in those volumes. The IH "part manual" is of absolutely no help in this regard...service part part numbers are different than numbers that were used on the assembly line regarding distributors and many other parts! This is a somewhat complicated thing to explain and if there is interest, I'll cover that in another thread.

The meaningful data/specs for the prestolite electronic distributors is covered in the cts 2313 manual set for m/y '78> m/y '80 Scout II. Keep in mind...all distributor specs shown in the ihc-produced literature reflect running the distributor ina test stand, not an engine so the values have to be "adjusted" accordingly.
 
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Here's a scan of the specs for both distributors you gave an id number for.

You can compare them and see they do have somewhat different characteristics overall.
 

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Thanks michael, I have that same manual, I just lent vol. 1 to the machinist. The one off my 345, 484778c91 4002b seems better right? More advance, and more spread out check points. A shop up the street has a test stand, ill see if its within specs. But what are my options if its not? Can I rebuild it cheap or does it need to be remfg.? Sorry I dont have my manual on hand.
 
78ih said:
thanks michael, I have that same manual, I just lent vol. 1 to the machinist. The one off my 345, 484778c91 4002b seems better right? More advance, and more spread out check points. A shop up the street has a test stand, ill see if its within specs. But what are my options if its not? Can I rebuild it cheap or does it need to be remfg.? Sorry I dont have my manual on hand.
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Yep...the 4002b would prolly be a "better" curve for your engine project.

Any shop that has a distributor machine and knows how to use it, can tweek the advance curve to nearly any settings desired.

The issue to watch for in actual engine operation would be a base timing that can be established around 10>12*btdc if running premium fuel at the compression ratio that Robert calc'd. But you must pay attention to any hint of over-advance (detonation) at a "cruise" throttle position and say 45>50mph ground speed.

The 4002r curve was most likely initiated as a method to eliminate light load/mid-rpm detonation when egr was not "active". That's my "theory" anyway!

This "curve" stuff is something that must just be worked out when the motor is operational, it can be done onna dyno (best method) but that is very time consuming and time is big dollars onna dyno!
 
Thanks, but what if the end play is too much? Sorry, vol. 1 of my manual would come in handy now.
 
78ih said:
thanks, but what if the end play is too much? Sorry, vol. 1 of my manual would come in handy now.
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Excessive end play allows the timing to "wander" as the helical drive gear thrusts up and down.

Max end play for that unit is 0.040", minimum is 0.035". I personally think even that minimum is too sloppy...I set 'em at 0.015">0.020". Use a thickness gauge to measure the actual endplay and then calc the thickness of the shim you need to bring it in. To "adjust" the end play, ya push the split pin out, pull the drive gear off and place a shim with proper thickness and a 0.500" id between the gear and the body. Then re-install the gear and set the spring pin. I have shims from 0.005">0.075" in approximately 0.005" increments for doing this. I buy the shims in bulk direct from msd.
 
Alright, as long as end play is dealt with, should it be tested on a stand or just installed and ran? How much am I looking at to have it recurved? The machine shop has a dyno. They might do this. He offered to set up that carb. Sorry again im missing vol. 1.
 
I'd stick the distributor in and go! No need to change the advance curve until the motor is run-in and you can drive the rig and determine if anything needs to be changed.
 
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