Upgraded the alternator

[m3f_Longboardsteez]

I recently replaced my alternator (from an 80a to a 140a). Both are bosh, so I expected an exact fit, but I was wrong. I had to file down part of the alternator housing to get the new one to fit. This was the least of my worries. After installing it I thought it was easy sailing from there. I reinstalled the serpentine belt and it broke in a matter of 20 minutes of driving. Mind you that that this belt is only 2 months old and had no issues until I reinstalled it. Could the new alternator require a longer belt to compensate the bigger pulley or did I just install it wrong? I uninstalled the idler puller to create more slack and make it easier to install the belt. After I reinstalled it, I ran the car. It ran for a good 20-30 minutes and broke while I was backing out a spot. Any suggestions?


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[m3f_M_Parallel]

Bigger pulley should be compensated for by the tensioner, unless it would be way bigger.


I can only guess it's not aligned perfectly straight. This would but side friction on the belt and than it won't last long.


You run a huge ICE install to need 140A? Or because it sounds cool?

[m3f_pbonsalb]

Is it possible you did not reinstall the belt properly or the idler pulley properly? There is a dimple in the idler that fixes its location and it is spring loaded. The belt wrap goes a certain way around all the pulleys and you may need to refer to a diagram to make sure you got it right.


It is also possible you got the wrong alternator. I converted from a Valeo 80 to a Bosch 140 years ago and have had no issues. I recall that there was a difference in pulley spacing between the Bosch and Valeo that was compensated for in alternator mounting, meaning the pulleys were not interchangeable without affecting belt alignment. If the Bosch unit you bought was not designed for the M50/S50/M52/S52, it may have a pulley alignment issue.


I changed to a 140A because I was running 2 small puller fans on the intercooler, 1 large puller on the radiator, 1 large pusher on the AC condenser, a larger fuel pump and a larger amplifier and did not want any issues with all the fans running at idle speed when they are often needed most and the alternator is putting out the least. But an 80A is lighter, saps less engine drive power, and works fine for most people. I would change back to one if I had one since I an running only 2 fans now (though both have 265 watt Bosch motors and can draw 20A each).

[m3f_M_Parallel]

Is it possible you did not reinstall the belt properly or the idler pulley properly? There is a dimple in the idler that fixes its location and it is spring loaded...

The idler (or deflecter pulley as BMW calls it) is a fixed position pulley with an offcentric bolthole. There is nothing to adjust.

[m3f_pbonsalb]

The idler (or deflecter pulley as BMW calls it) is a fixed position pulley with an offcentric bolthole. There is nothing to adjust.

There would be something to adjust if the OP did not reinstall the idler correctly with it rotated so the dimple is in the hole. Always worth suggesting someone who had issues after an install check the simple stuff that the OP disturbed immediately prior to the problem occurring.

[m3f_Braymond141]

The idler (or deflecter pulley as BMW calls it) is a fixed position pulley with an offcentric bolthole. There is nothing to adjust.

There is a locating pin on it, but it is not spring loaded. It must be held in place while tightening down otherwise it can be installed wrong.


Also, define "upgrade"? What is the increased parasitic drag from the 140 alt upgrading?

[m3f_M_Parallel]

There is a locating pin on it, but it is not spring loaded. It must be held in place while tightening down otherwise it can be installed wrong.

..

Oh yes, but that is so self-explanatory I didn't mention it. I meant once in place, there is no spring or hydraulics that put pressure on the belt i.e. fixed.

[m3f_pbonsalb]

I am one of those people who wants to help the OP get the job done. I'll leave you two to fight over details.

[m3f_Braymond141]

I am one of those people who wants to help the OP get the job done. I'll leave you two to fight over details.

I was actually helping you, but okay.

[m3f_terraphantm]

Also, define "upgrade"? What is the increased parasitic drag from the 140 alt upgrading?

The difference in parasitic drag will be minimal until you actually load the alternator past 80A, at which point you'll be glad you have the extra capacity (though I guess your point is it's useless if you aren't running anything that will draw the extra power like an audio system or large electric fan)

[m3f_Longboardsteez]

There would be something to adjust if the OP did not reinstall the idler correctly with it rotated so the dimple is in the hole. Always worth suggesting someone who had issues after an install check the simple stuff that the OP disturbed immediately prior to the problem occurring.

This is what I was hoping was the issue. I ignored in quick attempts to get my car running but next time around I'll take my time


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[m3f_M_Parallel]

I was actually helping you, but okay.

So was I.



Re-read if not clear (to OP).

[m3f_Braymond141]

The difference in parasitic drag will be minimal until you actually load the alternator past 80A, at which point you'll be glad you have the extra capacity (though I guess your point is it's useless if you aren't running anything that will draw the extra power like an audio system or large electric fan)

Yes I know. Similar to arguing the increase of removing the mechanical fan (on the E36 the single front AUX fan is more than sufficient to run alone so a puller fan adding power draw is irrelevant).


I am very partial to keep it simple and light while remaining well within in the means of the components. The 80amp fits that just fine. This is not an upgrade unless, as you said, the additional capacity is needed.


From another member.

140amp - from what I remember came on "cold-weather" package BMWs and convertibles.


+: higher amp ratings for cars with high amperage loads like powered convertible tops or higher power stereos


-: heavier in weight (like 1/3 easily), and parasitic drag of 1-2 hp.

[m3f_fiveightandten]

I'm surprised you had to do anything to the alternator. I didn't have that issue: http://www.m3forum.net/m3forum/showthread.php?t=213199


-Check the locating pin on the alternator idler pulley, as they suggested above.

-Check the belt routing.

-Slack the belt up a bit and spin all the accessories and pulleys by hand to make sure none of them are seized up and dragging on the belt.

[m3f_Longboardsteez]

To follow up, it was because the pin wasn't properly aligned. I fixed it and got everything working properly. Here's what's left with the old belt.


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