4.6L Alternator Rebuild Kit?

[BimmerM3inGA]

So it's been a bad week for the fleet. On my way to work Wednesday morning, I got a flat in my nearly new 2015 i3. No spare tire, and non-runflat tires mean waiting an hour for Roadside Assistance on the shoulder of I-75. Then, the next day the X5 4.6is that's been kicking my ass for the last 9 months stuck again. There was a very loud sound from under the hood and the engine would die if I let its speed drop to an idle.

Not wanting to attempt diagnosis in nice clothes (the wife and I were on our way to dinner), and not wanting to risk further damage, I called for a tow and waited another hour for the tow truck to arrive and drag its sorry carcass back to the house.

The problem this time is the alternator. The bearings are very rough and it's very difficult to spin the pulley. I've been doing some research and it seems that the bearing failure is fairly common, and the bearings themselves are available from BMW.

Has anyone tried this repair? What were the results? Is it worth it to spend $40 on a set a bearings, or should I just order a newly rebuilt Bosch alternator?

[X53Jay4.8is]

Originally Posted by BimmerM3inGA

So it's been a bad week for the fleet. On my way to work Wednesday morning, I got a flat in my nearly new 2015 i3. No spare tire, and non-runflat tires mean waiting an hour for Roadside Assistance on the shoulder of I-75. Then, the next day the X5 4.6is that's been kicking my ass for the last 9 months stuck again. There was a very loud sound from under the hood and the engine would die if I let its speed drop to an idle.

Not wanting to attempt diagnosis in nice clothes (the wife and I were on our way to dinner), and not wanting to risk further damage, I called for a tow and waited another hour for the tow truck to arrive and drag its sorry carcass back to the house.

The problem this time is the alternator. The bearings are very rough and it's very difficult to spin the pulley. I've been doing some research and it seems that the bearing failure is fairly common, and the bearings themselves are available from BMW.

Has anyone tried this repair? What were the results? Is it worth it to spend $40 on a set a bearings, or should I just order a newly rebuilt Bosch alternator?

Please just order a Bosch premium rebuilt alternator which includes the new pulley bearing rather than DIY repair the alternator yourself. I just put one on my 4.6is all is good .

[BimmerM3inGA]

There is some question about the quality of the parts used in the Bosch rebuilt alternators. IE: Chinese bearings. If I buy the parts myself, I can control what goes into it.

Even with the lower quality parts, the rebuilt units are expensive. The best price I've been able to find is about $400.

[X53Jay4.8is]

Originally Posted by BimmerM3inGA

There is some question about the quality of the parts used in the Bosch rebuilt alternators. IE: Chinese bearings. If I buy the parts myself, I can control what goes into it.

Even with the lower quality parts, the rebuilt units are expensive. The best price I've been able to find is about $400.

Well if you can get a better set of replacement parts then what is being used in the rebuilt bosch premium alternator and can complete the repair on the alternator yourself then its a no brainer. Get the parts and do the rebuild yourself. As matter of fact this will probably make a good DIY video for those that want to take the same route as you when the alternator fails.

[BimmerM3inGA]

I've been doing more research on this and it appears that the "Premium" Bosch rebuilt alternators do, in fact, use German-made parts. While all of the individual components that I've been able to find so far except for the bearings have questionable origins. It doesn't make sense to go to the trouble of removing the alternator and cracking it open to only change the bearings. Might as well do a full rebuild.

If I can find a source for the Bosch parts, I want to rebuild it myself - it doesn't look that complicated. But if I can't find authentic parts, I'll have to go with the rebuilt unit and hope that it really does contain the parts they say it does.

[oldskewel]

If you go the rebuild route, I would not order any parts until you are sure of the exact Alt you have in there. My '01 3.0i has a Valeo 120A, and my understanding is that the Bosch and Valeo's were used fairly interchangeably in that era.

The mileage on your car is probably important, since the brushes are a wear item. Mine lasted about 170k miles.

When you get to it, I'm sure you'll find that neither Bosch, Valeo, nor BMW actually makes the bearings in there. Probably Koyo, NSK, SKF, FAG, etc.

Since you mentioned your i3 problem ... if the car has no spare, would it make sense to carry a tire inflator (compressor) and a plug kit? I know that would not work for most people, but you sound like you'd be able to use it and be gone before a tow truck even gets there.

[BimmerM3inGA]

If you go the rebuild route, I would not order any parts until you are sure of the exact Alt you have in there. My '01 3.0i has a Valeo 120A, and my understanding is that the Bosch and Valeo's were used fairly interchangeably in that era.

The mileage on your car is probably important, since the brushes are a wear item. Mine lasted about 170k miles.

FWIW, V8 models like the 4.6is have water-cooled, brushless alternators. They are a very simple design. The only moving parts that touch anything are the bearings.

Since you mentioned your i3 problem ... if the car has no spare, would it make sense to carry a tire inflator (compressor) and a plug kit? I know that would not work for most people, but you sound like you'd be able to use it and be gone before a tow truck even gets there.

The i3 comes with a compressor and sealant. It doesn't have a jack, lug wrench, or any kind of patch kit. Whenever I get it back, I plan to get a small bottle jack, patch kit, and lug wrench to carry with me. In this case, though, none of that would have mattered. The hole in the tire was big enough for me to stick my finger through it.

The whole tire deal was very aggravating. What should have been a 15 minute inconvenience turned into a 2 1/2 hour ordeal. I get why BMW configured the car the way they did. But, sheesh, what a PITA!

[BimmerM3inGA]

I had a very enlightening conversation with a starter/alternator/generator engineer with Bosch. He was very familiar with this particular alternator and as luck would have it, I happened to talk to him on the same day that he was researching options to rebuild the alternator in his E39 540i M Sport.

To make a long story as short as possible, his advice was to buy the bearings, replace them, call it good. So I ordered the bearings. But when I opened up the alternator, it was nasty inside. The rotor had been rubbing on the stator and part of it had actually melted. I talked to the engineer again and his "gut feeling" was that it would probably still work fine. But that didn't give me much confidence. So I just coughed up the 400 bucks for a premium rebuilt alternator from Bosch - which is the only way to get a rebuilt alternator with genuine Bosch parts instead of Chinese junk.

So it's back together and running again. But for how long this time? I think I'm going to open a betting pool on what the next failure will be. Anybody want a piece of that action? Here are the top 10 potentials, in no particular order:

1. ABS Module
2. Transfer Case
3. Catalytic Converter(s)
4. SRS Module
5. Transmission
6. Power Steering Pump
7. A/C Compressor
8. Suspension Air Spring/Compressor
9. Oxygen Sensor(s)
10. I would say Navigation Computer, but it's already on the fritz

[X53Jay4.8is]

Originally Posted by BimmerM3inGA

I had a very enlightening conversation with a starter/alternator/generator engineer with Bosch. He was very familiar with this particular alternator and as luck would have it, I happened to talk to him on the same day that he was researching options to rebuild the alternator in his E39 540i M Sport.

To make a long story as short as possible, his advice was to buy the bearings, replace them, call it good. So I ordered the bearings. But when I opened up the alternator, it was nasty inside. The rotor had been rubbing on the stator and part of it had actually melted. I talked to the engineer again and his "gut feeling" was that it would probably still work fine. But that didn't give me much confidence. So I just coughed up the 400 bucks for a premium rebuilt alternator from Bosch - which is the only way to get a rebuilt alternator with genuine Bosch parts instead of Chinese junk.

So it's back together and running again. But for how long this time? I think I'm going to open a betting pool on what the next failure will be. Anybody want a piece of that action? Here are the top 10 potentials, in no particular order:

1. ABS Module
2. Transfer Case
3. Catalytic Converter(s)
4. SRS Module
5. Transmission
6. Power Steering Pump
7. A/C Compressor
8. Suspension Air Spring/Compressor
9. Oxygen Sensor(s)
10. I would say Navigation Computer, but it's already on the fritz

I'd say ABS module next in the form of trans fail safe error. I would strike the Navigation Computer off the list because its on the fritz and it wont leave you hanging from driving. It sounds like you are ready to sell your 4.6is?

[BimmerM3inGA]

It sounds like you are ready to sell your 4.6is?

Been ready. But I kind of shot myself in the foot by chronicling all the problems here!