MG Sports Cars

Greetings all,

The alternator on my factory V8 prototype decided to stop working. It still has the original Delco alternator (P.N. 7982707 / DN460) and I'd like to keep it with the car. I've been having charging issues for a bit and now it's given up the ghost. Voltage at the battery while running is only 12.2V. Based on this, I suspect the rectifier is toast (please correct me if my reasoning is faulty). I'm willing to rebuild it myself and figured I'd change what internals I can in the process (rectifier, voltage regulator, bearings, and brushes).

Back in the 80s, my father was able to get this alternator rebuilt at the Delco factory in our hometown of Anderson, IN. Alas, that factory is long gone so I sharpened up my google-fu to find part #s for key components.

Rectifier: OEM# 7982623, 7982659, 7982756, 7982772; non-OEM reference# RTF3983; Lucas# 21226107 and UBB700; Marelli 940038217
Regulator: OEM# 50551, 21226043, 7982685, 94648534; non-OEM VRG3693B; Lucas 21226043 and UCB702; Marelli 940038033
Brushes: OEM RX103E; non-OEM ABR5252
Front end bearing: OEM BRG6203; non-OEM BRG62032RS
Rear bearing: OEM 3472455; non-OEM BRG3906

I was able to find these from UK/Euro based auto electrical suppliers. Extensive parts cross reference searches at a couple of local autos parts stores yielded no results.

My questions to you gentlemen, does anyone know of a US based source for European Delco parts (or someone that might have these parts squirreled away)? I am also considering approaching two local and reputable auto electric rebuilders. Pending going to these guys, it there any shops in the US that any of you recommend?

Thank you,
Andy

That looks like a bog standard Delcotron from what I can see in the picture. If you want to keep the cases due to numbers or such your best bet is to go to the parts store and just buy a cheap rebuilt Delco to fit any GM and swap out the internals. The parts from any will work just fine, they are all interchangeable. If you want to upgrade you can get one with a higher amperage stator and use that. A matchstick or brake cleaner spray tube works to hold the brushes during reassembly. Or you could just take the new one and clock the cases to match yours and be done with it.

Jim

I just looked at the Rock Auto parts web site. A rebuild kit costs the same as a rebuilt alternator - about $30. You'll save $5 on the core charge and the lower cost of shipping the parts rather than the heavier alternator. It's not hard to rebuild an alternator, so if you're handy, I suggest doing it yourself.

Seems like that part number on the alternator, 7982707, is specific to MGB V8. Doing a web search gets a few hits related to original MGB V8 cars. Might as well keep it with the car.

Here are some more pics of the overall alternator. Alas, I don't believe it's a standard delcotron (e.g. 10SI, 12SI, etc.). That would make things far too easy! This one has 3 case screws and a Lucas connector. That's not to say that the internals aren't the same, or close, though. It may be worth dissecting one to see.

I had completely neglected to check Rockauto. They truly surprised me to even list the 3.5 as an engine option. They list a rebuilt alternator, brushes, and drive end bearing. However, the picture appears to be a Lucas unit (maybe the standard MGB unit?) With a bit more digging, I don't have much faith in their parts listings for the 3.5 cars as their dizzy cap listed is the 4-banger one. Ugh...

One other thing to note, I did learn that BL also put these alternators in Jensen-Healeys and some TR6 (other TR6 had a Lucas unit). Not sure if that helps, but it does open up asking around to some Triumph folks.

Yep, that one's different. Looks a bit like the old Delco with the external regulator but isn't that one either quite. The three tab connector is the unique bit.

Have you had it open yet? It could use the same diode pack, though obviously the regulator is different.

Jim

I'm pretty sure it's not at all hard to split the case if you wanted to look at the internals. There are some youtube videos that illustrate how to rebuild these alternators and it looks like they are quite easy. I've repaired alternators before, replacing rectifiers. It's not rocket surgery.

Open it up and post some pictures of the internals Andy.
I'll bet that one of us can match you up with the needed pieces.
More than likely your going to find a worn brush if it was charging sporadically.
That would make it a very easy fix.
The same alternator came on the non A/C TR7. The rebuilt Delco # is 334-1527, but you need to see it first as they interchange at will with the Lucas style.

Cheers
Fred

Well, I tried to open it up this weekend, but I'm having quite the difficulty removing the pulley/fan with hand tools. 30 years of corrosion has firmly cemented the nut onto the shaft and multiple days of penetrating lube didn't help. Fan orientation shows this thing rotates CCW, so I would think standard righty-tighty applies. Before I break out the flame wrench and/or other possible forms of automotive torture, any hints on getting this thing loose? A cohort suggested sticking a screwdriver into the fan / cooling holes, but I don't like the prospect of damaging the fan. I was thinking to try to loop the old V-belt in the pulley, tie it off somehow, then hit it with an impact.

Don't alternator shafts have an Allen head end that can be used to hold while undoing the nut?....nut should be standard right hand thread.
Edit: added photo from the 'net




Edited 1 time(s). Last edit at 03/07/2016 04:53PM by ex-tyke.

I use an impact wrench to take the nut off. Seems to work every time. The pulley is usually a fight.
Steve

Andy, Graham shows how to do. Looking at the pictures you posted there is an allen hole in the center of the shaft. Soak the nut and shaft over nite with PB Blaster, then add a little heat.

charles

Greetings,

Popped open the alternator over the weekend. After liberal applications of PB Blaster, some encouragement with a flame wrench, and two grown men leaning into it, that stubborn nut finally broke loose.

Here are pics of the business end of the alternator as well as the rectifier and voltage regulator.




I am able to discern the following part #s
V. Regulator - 7934605
Rectifier - 3472311

Google found some available parts for these #s, but all are overseas. I'll try to cross them at Napa /Autozone this evening.

Any idea what this piece is which connects the VR to the Rectifier?

That is called a diode trio, It provides a voltage signal to the regulator from the stator winding so the regulator can maintain the output. That and the rectifier package should be the same as in any domestic Delcotron. From your photos only the terminal lug position of the regulator is different.

Jim