Interesting alternator information/revelations

[boney]

1983 CJ7 -v-belt alternator issues.

I received this Jeep a handful of years ago with a bad alternator. Replaced it with whatever Napa Auto Parts said should be on the car. It was plug and play- that is, it fits the wiring in the car perfectly and I didn't look back. Until I realized that it doesn't charge at idle- and as I turn on lights and the HVAC fan the voltage drops. Mostly I've just dealt with it over the years because 1-it hasn't caused an issue and 2- it doesn't get driven every day.

So I dove into it today because I'm tired of thinking about it while driving.

The voltage drop with electrical load is because of the old and likely tired wiring and connections in the loom. With the RPM's up, the battery is getting 14.1V with everything on. At the dash it drops to about 13... To be addressed at a later date...

The alternator appears to be in good shape. There does not appear to be any issues with the diodes (as best as I can test with the volt-meter) and it is grounded well and the connections on the positive side of the system have no resistance.

It appears from research on the 'nets, that an alternator needs about 2400 RPM to produce power and that peak production happens at 6000 RPM.
With a crank pulley of 6.75 inches and alternator pulley of 2.5 inches, the ratio between the two is 2.7:1.

If the crank is turning at 750 RPM (roughly idle) the alternator is turning at about 2025 RPM.
I need 900 at the crank to turn the alternator at 2400 and 2200 RPM on the crank to reach 6000 at the Alt. But I don't have big electrical loads, so it's unlikely I'll ever need the full capacity of the alternator.

If I were to replace the alternator pulley with a 2.25 incher, then the alternator would be at 2250 RPM at idle. (3:1 ratio). That would put me closer to where I'd like to be... I haven't found any 2" pulleys available otherwise I'd go with that and have 2530-ish alternator RPM at idle. (3.375:1)

I'm curious if anyone else has found themselves down this rabbit hole and what solutions they've found tried.

 

[CJ]

Good post! Your found out one of the crazy things about what it takes to get the excitor circuit triggered on alternators. Unless you idle your Jeep 24/7 it's almost never an issue. One wire Delco types take even more RPMs.
Personally, I have never worried about it but I understand your concern. Most alternator shops have hundreds of old pullys laying around if you want to shop a little.

 

[hole]

When mine died I went with a GM CS144, which was probably overkill. CJ make a good suggestion, as long as you have a alternator shop nearby. Might try wrecking yards too for the pulley.

 

[boney]

Resurrecting an old thread.

I continue to have alternator issues, and I may have been chasing something that didn't exist.

Mostly, my alternator belts slip. The old pulley above. Then new, smaller diameter pulley, and now the new alternator, which I replaced while on a trip. No surprise here.

At highway speed, with anything more than the headlights on, the belts slip and I can watch my volt meter drop. So, no heater fan and headlights. So prevent this from continuing, I crank a little tighter on the adjustment until of course, I damage the bearings. Parking lot swap a long way from home.... I also blew out a water pump, but it didn't leak so I kept driving. Went 500 miles on one that wobbled all over the place and made a racket.

None of the belts anyone recommends for my 1983 I-6 seems to fit the profile of the pulleys. They don't sit low enough IMO, to be getting a good purchase. The latest, is that the shop tells me the belts I've been getting are the narrowest of all, and that's it. "There must be something wrong with your alternator." Apparently in the past, they consolidated belt widths?

FWIW, the power steering belt sits much lower in it's groove than the alternator belt, even though they're the same width.

Anyone on the forum have any wisdom? I've got 2 belts... one for the crank -> alternator -> water pump, and one for the crank -> water pump -> power steering pump.

Still trying to figure this out...

 

[Belizean]

boney I was wondering what bracket you have ? I bought a well used engine to rebuild. I wanted something with the brackets for alt. ps. Mine came with a bracket but I also had to use a few metal spacers where broken plastic had been used. Mine actually sits a little high in the pulley. I’ve seen better bracket on the I-6, which I would like to find.

 

[boney]

My PS bracket is a mix of cast and plate steel with about a bazillion bolts in it. It's slightly misaligned but I've never has a slip on the belt.

The alternator bracket looks pretty stock. The bottom one bolts up to both sides of the "sleeve" and the top is an arc that mimics the sweep of a pivoting alternator. Nothing special. Tightens down on the alt nice and solid, holds firm.

 

[Belizean]

Sounds like we have the same one.

 

[boney]

Okay, more information. As far as I can tell, the OEM part number is 8UT0126345. Everything recommended by a computer in a parts store is a 0.53 section width belt. After pulling my belts and measuring the width of the pulleys, I'm getting a hair bigger than 3/8" and a hair smaller than 7/16". This is a highly accurate measurement with a metal tape bent in there and eyeballed with 55 year old eyes. Also, I took a good look at the belt and there is a visible wear line where it is obvious the belt is not settling into the grooves. Interestingly, the grooves for the PS pump are wider. A full 1/2" and the 0.53 section width belt settles into them very, very nicely. So clearly, I'm dealing with 2 different belt width issues.

Me and ChatGPT, we went down a rabbit hole on belt profiles, section widths, lengths and all that. I stuck all the dimensions into it and it suggested a few belt sizes and widths. Then I told it I wanted to know where to find jeep specialty parts and v-belts. It gave up a ton of web sites, both Jeep and industrial supply.

Turns out thejeepsterman.com had a belt in almost exactly the size ChatGPT suggested I find. So here's the results for those who want to geek on this- or are at least having belt slippage issues with "modern" belts.

NOT RIGHT: Any belt size with a 0.53" section width. So skip the 7575, or 15425 or whatever Napa and O'Reilly say fit.

RIGHT: (pending delivery and installation) Bando RPF 2430. AKA 9.5 by 1090. It is a 3/8" section width belt at about 43 inches in length. This should sit lower in the pulleys and give me a full belt worth of grip- hopefully eliminating the slip I'm getting under alternator load.

I'll update with the results.