M939 NHC250 Delco Remy 33si Alternator Upgrade

Swamp Donkey

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Before I get started I must give credit where it's due. Throughout this process, 74M35A2 has been an infinite source of knowledge on the specifics and details of this alternator. He stayed with me from the purchase, to when I fired it up after I was done. Without him, I'd still be using trial and error to make this work, which we all know can be costly and time consuming.

Alternator details:

20160615_202151.jpg

This is a New Genuine Delco Remy 33si brushless alternator rated for 24v and 100A [NSN 2920-01-484-9161 - P/N 3400698]. It was designed for severe duty applications, like heavy equipment, and has features that help prevent moisture, dust, corrosion and heat damage. It is right at 5 pounds lighter than the stock alternator and is also shorter, as seen in the comparison picture below. It is temperature compensated and uses a single wire connection, although there are provisions for other configurations there too.

This will not be an economical upgrade for most folks since the price of these is on the high side. These were used on a few MVs though, so they can be found in surplus, which is where I got mine. Buying one straight from a civilian dealer would not be very cost effective. I decided to upgrade mainly due to the Warn winch I use. Everything is LED on the truck so the winch is the only real load. The high failure rate of the factory alternator never left me with a warm fuzzy feeling that it'd be there when I needed it most.

The install:
This is a comparison picture between new and old. I placed them with the pulleys square to each other to give an idea of the differences. The pulley will have to line up so everything else will have to fall in line. I also have the bracket lined up so you can see what will need to be adapted to make it work. I didn't find a bolt on bracket that would work so I went the modification route.

The bolt holes on the engine side of the bracket are slotted. With the factory alternator the bracket is all the way to the back. With the shorter shaft on the new alternator the bracket will need to be all the way forward to line things up.

The original bracket is a long version and the alternator needs a short one, so spacers will have to be used. The original holes are smaller, maybe 5/16" bolts, and the new alternator uses 1/2" bolts so the holes will need to be drilled out on the alternator side of the bracket. I then used some 1/2"ID x 3/4"OD seamless round stock to make a rear spacer. I used this so there would be plenty of meat for a solid weld to the bracket. A long bolt is used on the rear ear and a standard length bolt is used on the front with no spacer. This places the alternator in alignment with the drive pulley.

20160616_024713.jpg

The tension bar will have to be drilled to 1/2" too. I flipped the bar around and drilled the hole instead of the slot. This was much easier to do. The adjustment end is now on the engine side of the bar. A spacer will also be needed here to keep the bar square to everything else. I welded the spacer to the bar using the same material as the rear spacer.

20160616_031605.jpg

Since the new pulley is a smaller diameter, some shorter belts will be needed.

20160616_031537.jpg

Trial and error on belt sizes. The washers on the tension bar have since been replaced with a welded spacer.

20160616_230339.jpg

The positive wire goes to the POS terminal and the ground wire goes to the case.

20160616_231629.jpg

The finished product. This was during a test run. The bracket and tension bar now have the spacers welded in place.

https://youtu.be/Du7vdp9uhQg

If you happen upon one of these for a good price then it's not a bad install. You'll end up with a quality severe duty alternator you'll never question again.

Cost analysis:
Alternator -$70
Pulley - $13.50
Shorter matched V-belts - $14.00
Misc. - $20
Total - $117.50
 

74M35A2

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Nice thing here about changing to any alt besides the mil one is that it will not over-volt on an "incorrect" shut down procedure. You won't zap your ABS, PCB, or anything else that has letters in it. The alt above can be ran as a single wire unit, meaning it just has a single large red battery cable, usually patched to the back of the starter as a shorter path than the batt box. Brush-less is nice, they can withstand higher temp, and can have a longer life, but slightly lower output, especially at idle. Anything is better than the MV ones.
 

74M35A2

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I didn't sell SD that alternator, I just advised him about it and fitment/wiring/etc. He was kind of surprised I talked him through it even though it didn't come from me. I don't really care, mine are pricy and I don't blame people for going elsewhere to get a better deal, we all do it. The above is a unit I don't sell anyway. G, the alternator 8.3 24v alternator heading your way does require switched 24+ ignition lead (already there anyway). The 12v 277 amp one likely does not. I will test that today before it ships out.
 

simp5782

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Could you post the part numbers for the pulley and belts that you used? I have an alternator similar to yours I have been planning on doing with mine given the fact that I do about 1,500miles a month in mine so I am dreading the alternator gives out while driving at night scenario. I keep an extra used alternator in a side box but who knows how long it would last.

Being that you can't get them rebuilt anymore. The local alternator rebuilders her just get you a NOS from Memphis equipment.
 

Swamp Donkey

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I didn't sell SD that alternator, I just advised him about it and fitment/wiring/etc. He was kind of surprised I talked him through it even though it didn't come from me. I don't really care, mine are pricy and I don't blame people for going elsewhere to get a better deal, we all do it. The above is a unit I don't sell anyway. G, the alternator 8.3 24v alternator heading your way does require switched 24+ ignition lead (already there anyway). The 12v 277 amp one likely does not. I will test that today before it ships out.
I could've been a little clearer. This alternator came from military surplus. 74M just assisted me in deciding if it was an alternator that would work for me and the technical aspect of making it work. I've changed out many alternators over the years but it was always a direct replacement. Fitment, correct pulley size and swapping to a one wire system were all places I had questions. He came through in all catagories, and yes, I was a little suprised by the effort he put forth.

I just happened across this particular one. It was already a good price for a new name brand alternator and I knew I could get it even cheaper than that with some arm twistng. It came from a local surplus seller. I brought it up here because they can possibly be found cheap and easily adapted. 74M and I had discussed the civilian price and why it wouldn't make for sense to go this route unless it could be picked up cheap. This is why I mentioned it being used on various military vehicles. They may end up in surplus and had for a more reasonable price.
 

Swamp Donkey

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Could you post the part numbers for the pulley and belts that you used? I have an alternator similar to yours I have been planning on doing with mine given the fact that I do about 1,500miles a month in mine so I am dreading the alternator gives out while driving at night scenario. I keep an extra used alternator in a side box but who knows how long it would last.

Being that you can't get them rebuilt anymore. The local alternator rebuilders her just get you a NOS from Memphis equipment.
The pulley is just a generic pulley. Doesn't really have a part number listed. I got it from Ebay for $13.50. They can be had with or without a keyway, which doesn't matter either way since it's a smooth shaft. The main specs you need are that it is 3-1/8" in diameter and has a 7/8" bore. Measure yours to make sure it has a 7/8" shaft before you buy though.
 

grendel

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You guys should buy through 74M. Outstanding products, service with decent pricing. My father always said quick, fast or cheap. Pick two, no one gets all three. I bought two complete truck's electrical systems from him. He's helping me retrofit a serpentine belt set up on a Caterpillar 3406B that never had it.
 

Swamp Donkey

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You guys should buy through 74M. Outstanding products, service with decent pricing. My father always said quick, fast or cheap. Pick two, no one gets all three. I bought two complete truck's electrical systems from him. He's helping me retrofit a serpentine belt set up on a Caterpillar 3406B that never had it.
I completely agree that what he is selling is a really nice upgrade for the 8.3L and he supports the product very well. He has also said that he doesn't have anything for the NHC250. This shouldn't detract from what he sells because I support what he's selling too. I just can't put it on my truck. :mrgreen:
 

74M35A2

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First off, get the best deal you can for what you want. I could buy $89 Chinese Delco clones and resell them to you for the 250, but you guys can do that yourself without a markup. So instead, I bring over 24v high output 130 amp non-Chinese units from the European market where they utilized, they fit 8.3 only due to their serpentine pulley and non-standard shaft diameter. A few members sell the Chinese 24v Delco cloner for 250 engine use, and they offer a fair price and warranty, and actually answer the phone. What is nice there is that they include all the required fasteners and such to adopt it to the military bracket. I'm a meanie and just tell you to buy the proper cast Cummins bracket. The people that buy my alt really want it, because they pay for it, about $490 all inclusive by the time it is properly on their 8.3. I do offer a 3 year warranty though. We had a supplier come in one time and their opening line was "Buy the best components you can.". It kind of stuck with me. I'll support anybody on any issue I can, especially starter/alternator stuff, regardless of where they got it from. There are so many better options today, and most reasonably priced. By everybody here contributing, it makes it just a little bit easier for all of us to enjoy these. I honestly sell less than one starter or alternator a month, and when doing so the profit margin is minimal, so it for sure is not making the house payment. I do it more to bring the modern technology into your hands via knowing what fits and not.
 
Last edited:

davo727

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This is a good thread. Do you guys know if the 33si style that you used will fit ok on a 939A2 8.3? I see that it will have the hinge mount at the top on 8.3 as compared to the bottom on your 250 cummins. I see in the 33si specs that they weigh about 30% more than a 21si so maybe more reliable??
 

74M35A2

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Yes it will fit and work, the alternator is just flipped over. J-180 defines an SAE mounting pattern. The only difference is the 250 engine requires a double v belt pulley with more standoff to it or to shim the alternator forward like done here. The 8.3 uses an 8 groove with no additional standoff built into it. The mass of an alternator has nothing to do with its longevity, that is kind of a misconception here. The cooling ability of the design and the thermal rating/quality of the power electronics are mostly tied to the reliability of the unit.
 

Shirehorse

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Dead thread revival.

What did you do with wire 566?

From my research, wire 568 is the excite wire, and wire 566 is the starter engagement with engine running prevention.

Brian
 

gstirling

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hey my new post and your old one... almost the same... i missed finding yours when i searched around on the site. guess i should have put mine on the back of yours and kept the thread topics clean. 74M35a has good stuff/advice. prices has gone up a a bit...LOL
 

simp5782

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Dead thread revival.

What did you do with wire 566?

From my research, wire 568 is the excite wire, and wire 566 is the starter engagement with engine running prevention.

Brian
Just tape the wires up. Run a direct power wire from alternator to the batteries since it's closer and run a ground from the alternator to the block there or the frame stud under the radiator support. Basically eliminating that harness section completely

Sent from my SM-G965U using Tapatalk
 

74M35A2

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Engine block ground wire is pretty weak since the block grounded loads are small to none. If you are upgrading the alternator output, best to run both alternator + and - wires back to the starter + and - terminals, since these are heavy cables back to the batteries. That is how todays over the road trucks are wired.

The starter re-engagement prevention wire (small circuit board within some PCB’s) goes to the alternator AC output terminal, R on the Delco/clone you are installing.
 

Owen0326

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I didn't sell SD that alternator, I just advised him about it and fitment/wiring/etc. He was kind of surprised I talked him through it even though it didn't come from me. I don't really care, mine are pricy and I don't blame people for going elsewhere to get a better deal, we all do it. The above is a unit I don't sell anyway. G, the alternator 8.3 24v alternator heading your way does require switched 24+ ignition lead (already there anyway). The 12v 277 amp one likely does not. I will test that today before it ships out.

Do you still sell the needed parts to upgrade the alternator on a m818??
 
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