Delco 24si alternator install on nhc250

[BenRoberts]

Got a 24si alternator from 74m35a2 and here is how the installation went. On first mock up it was clear the pulley was going to sit to far forward. To combat this the bracket was removed and machined to make it adjustable next since the 2 tabs for mounting on the bottom of the alternator were nowhere close to fitting the stock bracket a new spacer was machined with a 3/8 hole. I went with a 3/8 hole to make the spacer more stout. Before spacer after spacer since this unit has a smaller pulley shorter belt were a must to get proper tension on the belts. I found napa 7460 to work just fine the larger pulley off the stock unit I was informed would not change properly at idle. No modification is needed on the top bracket. It's flexible enough to bend as the lower bolts are tightened. as far as electrical goes if using the stock wiring the plug in exciter wire from the PCB is not used and will be tied up out of the way. The small wire is power and the slightly bigger wire grounds to the case. I bigger eyelet on the power wire will be necessary. Alt performs great and I hope I covered it all. Not a bad install at the end of the day.

 

[74M35A2]

Glad you like it. I have a shorter pulley available next time, this was kind of an experimental install of a nice compact modern unit onto a 250 engine. Bracket slots were a great idea!

I do have one more of these units available for a bargin basement price. Genuine Delco unit, not Chinese. Will fit 8.3L or 250, with bracket mods or civilian bracket.

Great output, single B+ wire operation, twin internal fans, light, compact, fail-safe, and reliable. They do not over-volt. Ben can now shut his truck off in any switch order safely, and not wipe out his ABS module.

 

[Dwnorton1]

Installed one on M813A1, NH250. Truck came without alternator. Stock belts worked fine, which is blessing because it would take 1/2 day to get everything loosened up to install new ones. Had to add one washer as a spacer or rear of bracket. Ordered the one listed for the for M35 multifuel. Cannot beat the price. Will send some pics when I get home.

 

[Dwnorton1]

As promised.

 

[BenRoberts]

That must be the other pulley he spoke of. The one on mine stuck out a mile

 

[74M35A2]

The unit above appears to be a Chinese Delco clone. I don't think that one was sourced through me (which is OK, I don't care), as I only had one Chinese unit for benchmarking, and it sold to a guy in an emergency need for a low cost unit.

There are 2 different common pulley stand-off heights available. I don't have access to a 250 engine, so just trying to guess as to what is needed. Have to fab the mount somewhat anyway. Still worth it in the end, even with a clone unit.

Ben, you did a great job on your bracket. Always encourage adjustability.

 

[Dwnorton1]

I'm sorry. Not sure where I got it now.

 

[BenRoberts]

Mine is still charging great. Should have done it in the beginning

 

[jonesal]

I'm trying to do this conversion on my M923 with a NHC250. Are there any part numbers anyone can provide for both the alternator and especially the pulley. Finding the right pulley seems to be the key but I can't find any part numbers anywhere! Thanks.

 

[74M35A2]

I'm trying to do this conversion on my M923 with a NHC250. Are there any part numbers anyone can provide for both the alternator and especially the pulley. Finding the right pulley seems to be the key but I can't find any part numbers anywhere! Thanks.

Not a fixed number. The 250 installs are pretty much backyard brew. Of the available pullies, some have different offsets. So, the amount of pulley offset will coincide with however you are configuring your bracket.

 

[Superthermal]

In looking at these 33SI series style alternators I do not see a balance wire for the 24V system pairs of batteries (For this example lets just say we have two batteries). This would normally give the "lower"-"A" battery a boost of amps to ensure the two batteries "A" and "B" are equal in voltage/charge level.

A reasonable explanation of this issue is described here along with a bunch of pages trying to sell a solution to the issue.

https://www.waytekwire.com/datasheet/extend%20battery%20life.pdf

One reason I ask, is I had planed on running some 12V accessories like the link above points out will create this imbalance issue. How are we working around this when a 33SI or similar alternator is used in the 24V system.

One way I guess would be to use a 24 to 12V converter and use that for all 12V accessories.
I have two matched batteries currently with the original balance wire style alternator, but know its days are numbered. Looking for the clear road to follow down the road.
Thoughts?

 

[74M35A2]

In looking at these 33SI series style alternators I do not see a balance wire for the 24V system pairs of batteries (For this example lets just say we have two batteries). This would normally give the "lower"-"A" battery a boost of amps to ensure the two batteries "A" and "B" are equal in voltage/charge level.

A reasonable explanation of this issue is described here along with a bunch of pages trying to sell a solution to the issue.

https://www.waytekwire.com/datasheet/extend%20battery%20life.pdf

One reason I ask, is I had planed on running some 12V accessories like the link above points out will create this imbalance issue. How are we working around this when a 33SI or similar alternator is used in the 24V system.

One way I guess would be to use a 24 to 12V converter and use that for all 12V accessories.
I have two matched batteries currently with the original balance wire style alternator, but know its days are numbered. Looking for the clear road to follow down the road.
Thoughts?

That’s a separate new thread topic, and you’ll get a wide variety of responses on this topic, but the original military design and installation of pulling 12v in these trucks is to just take it off of the ground side battery with no regard to balancing anything.