Hi,
I replaced the failed Valeo 80amp alternator on my 1993 325is with a new Bosch 140amp alternator. I used the original pulley. But when I installed the new Bosch alternator, the pulley did not line up with the other pulleys- it protruded two ribs of the 6-ribbed belt further out than with the original alternator, so when I turned the engine over, the belt moved two ribs closer to the alternator, (leaving only 4 of the 6 ribs on the pulley) to its natural position in which it was running true.
Before buying anything, I had gone to the dealership to ask about the correct alternator. They gave me the correct 140amp alternator part as 12-31-1-744-567 which agrees with the ETK. I ordered the car-specific Bosch 140amp alternator from Zygmunt Motors- there were no numbers on the alternator I could match with BMW numbers but I assumed it was correct. Closer comparison of the two alternators revealed that the face of the Valeo alternator was flat while the face of the new Bosch protrudes somewhat, about the width of two ribs. There is a collar on the pulley (~8mm) which is about the same as the width of two ribs but I couldn't find any information about a different pulley. Is there a collarless pulley?
Anyway, all that is to tell you that I thought I did the necessary homework to get the correct parts. The question is- can anyone help me resolve my problem? Thanks.

David Lamson
Durham, NC

Is the pulley reversable?

Is the pulley reversable?

That's a good question- in addition to the collar, the pulley also has a flange (or whatever it's called.) The collar and flange combined are as long length as the shaft that the pulley is bolted to, therefore it would be impossible to reverse the pulley. I took a picture of the two alternators (Bosch has the pulley.) You can sort of see in the picture the flat face of the Valeo and the somewhat protruding face of the Bosch. Thanks.

David Lamson
Durham, NC

At least I hope the picture comes through- it doesn't show up in the preview.

Places that sell underdrive pullies, like Evosport, ask whether you have a Bosch or Valeo alternator when you order their kit. Kind of indicates that there is a difference between the pullies for the different alternators. I also remember that someone on this board got the pulley for the wrong alternator from Turner, and it caused all sorts of problems.

So, I suggest you get back together with your parts guy and find the part number for the pulley for the Bosch alternator. Or, you might want to talk to the guys at Evosport, since it sounds like they've already done the research...

Jim

Does anybody know what model year bmw started using the Bosch alternator?

BOM, there is another pulley from another BMW model that uses the 140 amp alternator that will work. You will need to search your ETK to locate it. The 140 amp specific pulley must match up to the alternator.

I also recall that someone else did the same replacement and ground down the stock pulley's flange. Don't do that!

Good luck

Thanks all, I'll take a trip to the parts department with my two alternators and let you know how it works out.

David Lamson
Durham, NC

any results?

What were your findings?

Cobra Jet and others,

My old alternator was an 80amp Valeo, BMW part number 12-31-1-735-743. I don't know the part number of the pulley. My dealer told me the correct Bosch 140amp alternator for my '93 325is was BMW part number 12-31-1-744-567. Since Bimmerparts.com had a Bosch 140amp alternator which is supposed to be specific for my car for $100 less than the dealership price (even with my BMWCCA 10% discount) I bought my alternator from Bimmerparts.com ($260.+ $60. core.) There is no associated BMW part number- the Bosch number is ALU739X, Bimmerparts.com number F4000-51082.
I went to my BMW dealership today (Performance in Chapel Hill, which has a very nice parts department.) They told me the correct pulley for that Bosch alternator was BMW part number 12-31-1-432-988 which I ordered for $21. + tax. That BMW number is listed on ETK as a pulley option for the Bosch 140amp alternator 12-31-1-738-352. Whether it works or not I will find out later this week when I get my new pulley. I will let you know how it goes so that maybe others won't have this problem.

David Lamson
Durham, NC

thanks for the response David. The reason I was was asking was because I was going to upgrade my 95 M3 alternator to the 140 unit such as you did.

The pulley problem peaked my curiousity more than anything, because I cannot do the job and have excessive "down time". I was planning on doing what you did - simple purchase & swap... although, it seems the swap was not just "plug & play". :)

Please let us know how it all works out. There must be some difference in the design of the pulleys, maybe not as large of a "collar" on the one for the Bosch alt...?

You might want to think about just upgrading to some underdrive pullies. Specify that you need one for a bosche unit.

Dan

Hey David - was your parts swap a success? Did the other correct pulley come in, if so - can you list the correct parts (alt & matching pulley)?

If you did get it to work, do you notice any difference with the new 140a alt installed?

Thanks again and have a great upcoming New Year!

Guys, can you tell me whats the advantage of upgrading to the 140amp unit over the 80amp unit?

Im planning on getting the evosport pullies, and im contemplating whether I should purchase the 140amp unit. But because the evosport pullies would be underdriving it, I dont see what difference it would make.

If you have a high powered stereo, you're gonna want the 140 Amp unit over the 80 Amp unit. I don't think the belt will 'drain' more power from the engine, it's just that the coils are bigger to produce more amperage.

Good luck!
Wes
'95 M3

How can you tell which alternator you have? I'm about to do a stereo install and would prefer to have the 140, but don't want to buy one only to find out I already have one in the car!

I almost hate to post this reply but here it is.

This from my previous posts in this thread:

My old alternator was an 80amp Valeo, BMW part number 12-31-1-735-743. I don't know the part number of the pulley. My dealer told me the correct Bosch 140amp alternator for my '93 325is was BMW part number 12-31-1-744-567. Since Bimmerparts.com had a Bosch 140amp alternator which is supposed to be specific for my car for $100 less than the dealership price, I bought my alternator from Bimmerparts.com. There is no associated BMW part number- the Bosch number is ALU739X, Bimmerparts.com number F4000-51082.
But when I installed the new Bosch alternator, the pulley did not line up with the other pulleys- it protruded two ribs of the 6-ribbed belt further out than with the original alternator, so when I turned the engine over, the belt moved two ribs closer to the alternator, (leaving only 4 of the 6 ribs on the pulley) to its natural position in which it was running true.
I went to my BMW dealership today who told me the correct pulley for that Bosch alternator was BMW part number 12-31-1-432-988 which I ordered.

OK now the new. I didn't take a picture, but the shoulder on the new pulley is shorter by about the width of two ribs of the belt, which is what I expected if it were correct. I installed the new alternator/ new pulley, and the belt lined up properly- all good. I turned the key and a small puff of smoke came from the front right of the engine compartment (standing in front of the car looking at the engine.) I couldn't tell what the source was. It could have been the alternator- it's in that general area.

All I did to get the new alternator in was:
1) Remove the negative terminal from the battery.
2) Remove the upper radiator hose.
3) Remove alternator belt .
4) Remove the fan.
5) Remove the intake air temp. sensor? from intake air filter housing (I have cold air intake, not entire filter housing.)
6) Remove radiator fan.
7) Remove upper and lower alternator bolts.
8) Remove alternator wires.
9) Remove alternator.
Change pulley and reverse procedure. So other than the different alternator, I can't think of anything that would have caused a puff of smoke. I'll check the alternator wires to see if it's anything obvious, but unless I come up with a new idea, I wait until after January 6 when my mechanic gets back.

DocWyte, from underneath the car, I could just see the dirty plate on my old altenator. You can see it in the picture in one of my previous posts. But you're talking several hundred dollars if you do the work yourself, so I would avoid it unless necessary. I did it only because my old one died at 175K miles.

Check your fuses, sounds like you may have cooked one. You may need a larger fuse given that you are running alot more amperage now. Cehck the connections on the back of the alternator also. good luck

The story ended happily...

I checked all the fuses- all OK. I could see no wires that showed a sign of a short or anything else that might have caused a puff of smoke. I removed the alternator and checked out its wiring- looked OK. I reinstalled the alternator and tried to start the car again. Three times I cranked the engine for 12-15 seconds- the engine was firing on some cylinders, but just not starting. I could smell gas afterward so I suspected that I had flooded the engine.

My friend and I surmised: if the car was firing it was getting a spark. If it was getting a spark then it should be getting fuel and the car should start. We jumped the car from his Chevy van and with both clutch and accelerator fully depressed, I let it turn over until it finally started- probably 20-25 seconds. What caused the puff of smoke I had seen the first time I tried to start the car? A backfire through the cold air intake perhaps?

Anyway, bottom line. I'm now getting 12.2 volts across the battery with the engine off, and 14 volts with the engine running, so the alternator is working. Thanks for all your suggestions and if you have any questions let me know.

David Lamson
Durham, NC

David,

Can you just list the correct part numbers for the 140a alternator and the correct pulley for that unit?

I keep reading through the threads here that you posted, but I don't want to be confused with getting the incorrect #'s.... it's a little confusing deciphering what your final results were (corerct parts).

Thank you very much and this is a VERY informative thread about the 140a alt.

Best regards,
Phil

I am also interested in knowing.

The interest from Cobra Jet and babybluem3 raises a good point. My car is a 1993 325is. The information I am giving is for that car. I don't know for sure what the correct part numbers are for an M3 from the same year for example- they may be the same but they may be different (I just gave a quick look through my ETK for mid-90's M3 alternators, and it looks like they either came with 105 amp or 115 amp alternators- different than mine.) But here are the numbers I found for my car.

Bosch 140 amp alternator- BMW number 12-31-1-744-567.

Pulley for that alternator- BMW number 12-31-1-432-988.

Bosch number of the 140 amp alternator I put on my car- ALU739X.

Bimmerparts.com number for the Bosch ALU739X 140 amp alternator- F4000-51082.

The diameter of the two pulleys I have (one for the Valeo 80 amp and the other the 140 amp Bosch) are the same (55mm.) It is only the depth of the pulley that is different. I recommend that you either call your BMW parts department (hit or miss depending on your local dealership) or call Chris at bimmerparts.com (Zygmunt Motors) and ask him. I'm sure he could give you the correct information. (I am only a customer of Zygmunt.)
phone- 215-348-3121
email address- cmuzyy@aol.com

Good luck. See you on the track.

David Lamson
Durham, NC

'I don't think the belt will 'drain' more power from the engine, it's just that the coils are bigger to produce more amperage. '

the above is incorrect...u never get something for nothing....the more power an alt produces is the more power u lose from the engine that can be doing work (wooping mustangs :) )....that being said lets do a little math....lets go from 80 to 140A and see approximately how much power you are losing....140-80=60A.... Power=Current x Voltage .. 60Ax14.4V=864w.. 1HP=~746w.. so with losses u might lose 2HP or a little less with this upgrade when the alt is under max load..the above numbers are approximate but pretty close.....
Kevin

Kevin, I'm planning on using the evosport pullies. So in theory, would the performance pullies on a valeo free up more power vs having them on the 140amp bosch?

u will have the same gains from the pullies either way, its just that now u have greater losses from the larger alternator whihc will cut your TOTAL gain HP....whether u will feel the difference either way is moot and i honestly doubt u will...
Kevin

I agree the difference between the two alternators will be slight enough to be insignificant.
Just remember, if you use underdrive pulley on any alternator, your charging rate at idle will be severely diminished. Use wisely.

Hmmmm. I wonder if this setup that davidlamson did will work on my 95 M3? Can anyone confirm that the 140A alt will work in my 95 M3 with the parts descrived above for the 140A alt and alt pulley?

TIA

Also, Did you have to but the voltage regulator and other accessories seperately or was the pulley the only other part you had to buy to get this working in your car?