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E34 M50B25TU Bosch Alternator

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Checked the alternator fitted to my 525i with VANOS and it's rated at 140A, which is a bit strange, considering that I've got a bog-standard 525i with no A/C, OBC or anything fancy like that.....Well, I've got a sunroof if that makes a difference.

 

It's genuine BMW, but it's difficult to say whether it's the original from factory or possibly it was changed in the past.....How would you find out what's the correct alternator rating required for the car? Can it be 140A, despite not having any special equipment?

 

The BMW part number on mine is 12311738351, which RealOEM says was only fitted to E34 520i, 525i and 525ix Tourings for some reason? Makes no sense...Why only Tourings?

 

Putting my VIN into RealOEM brings up a choice of 2 alternators - 80A and 140A. The Bosch parts catalogue also gives me a choice of 2, being 90A and 140A. EuroCarParts has a choice of 3 for Bosch models, including 90A, 140A and 105A.

 

I will probably go with whatever's on the car, but I found it a bit unusual having a high-rated alternator on a low spec model?

 

Any thoughts?

 

 

 

 

 

 

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I think most were given the higher rated alternator as standard to allow options to be added by the dealer. You can use a vin decoder and see what it was fitted with. It’s option s571a reinforced power supply.

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20 hours ago, MikeTheSmith said:

I think most were given the higher rated alternator as standard to allow options to be added by the dealer. You can use a vin decoder and see what it was fitted with. It’s option s571a reinforced power supply.

 

Checked the options list from my VIN and yes, you're right, mine has the S571A reinforced power supply....That explains things then. Thanks

 

boiliebasher, 140A alternator on a V8 model would make sense, even on a basic spec one - at the end of the day, it's a V8, so whatever part you look at, it's going to be bigger and stronger vs any straight 6 engine or any smaller engine.

 

Called ECP today to confirm if they had the correct Bosch 140A alternator, and they do, which is good news, so that's sorted.

 

Don't fancy creating a separate thread for the starter motor, but ECP gives me a choice of 2 - essentially, the only difference is that one has plain bolt holes and the other one has threaded holes...

 

I've read somewhere that starter motors with threaded holes were fitted to later models, but you can also fit them even if your original has plain holes? Is this correct? Worst case, I may have to buy both and then just return the wrong one...

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Mine has the same alt.

 

Ac model with no extra electrics tbh

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Just out of curiosity what's the issue with your alternator?! Depending on what exactly is wrong with it, they can sometimes be refurbished. 

Edited by boiliebasher

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7 minutes ago, boiliebasher said:

Just out of curiosity what's the issue with your alternator?! Depending on what exactly is wrong with it, they can sometimes be refurbished. 

 

It's just making a slight whining noise all the time.

 

I'm sure there are more cost-effective ways of getting this sorted, possibly just replacing the voltage regulator, but it looks to be the original alternator from factory, i.e. 27 years old, so I don't really want to take any chances of doing any repairs - better just put a new one and be done with it.

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Anyone changed the starter motor on the M50? Any difference between the one with plain bolt holes and the threaded one? Are they interchangeable or better get both and fit whatever matches with the original on the car?

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What is the starter motor out of I changed mine with one out of an e39, mine is a 94

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Regarding the starter motors, turns out both types were used, depending on the manufacturer year - the threaded ones are more modern with reinforced mounting holes, so no need for a support bracket, as the starter motor is shorter, and also easier to install, because it's only held with bolts from the transmission side - no nuts required on the engine side.

 

Here are some useful threads on the subject, they mention E36, but it's the same thing on the E34:

 

https://www.bimmerforums.com/forum/showthread.php?558140-Replacing-your-starter-in-an-E36-Read-this!

 

http://m3forum.net/m3forum/showthread.php?t=271146

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I think I managed to fit an E36 starter motor on my M50'd E34 a few years back. Had to swap some parts over as it wasn't an exact match but it got me out of trouble as I was in France at the time and the local motor factors wanted ridiculous money for a new one!  

Edited by boiliebasher

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