Which alternator?

[parlant]

Hello,

As I progress on achieving the full Street worthiness of my e24, I’m considering a new alternator: when the engine is on, at idle I can see a very faint flicker of the battery light now and again. However, It becomes stronger and more frequent when I turn on the air conditioner.

Also, in the instrument panel, the fuel indicator twitches a bit.

I’ve cleaned out the main electrical ground points in the engine bay, to take that factor out of the equation: Chassis to hood, bottom left of valve cover, and the ground point next to the battery. I also don’t believe there are any vacuum leaks though I have yet to replace the air slide valve that’s located under the MAF. It doesn’t look bad though.

I believe this leaves me with checking the alternator and voltage regulator. I think I might as well buy a new unit. Also, looks like the one I have right now has been fixed already. There’s a warranty sticker on it and on the VR.

I’ve visited FCPEuro, Pelican, and Amazon and they all lead to Bosch model AL46X, 80 amp. The part number I see on realoem.com states that it’s a 90amps alternator though.

I’d like to get advice on the group here about the correctness of the suggested alternator or alternate (better) models I can buy instead. My e24 is a Euro, late 1982 635csi.

thanks in advance for any help!

[parlant]

Bump
Seems like I can put a 90 amp alternator (such as a Bosch AL49X) from the later model e24s, the only difference being that the early model alternators have rubber bushings while the later model ones have solid fixings. This aside, I can simply install a later model alternator? Can anyone please confirm whether it's that simple? Might as well install a later model especially since there seems to be hardly any difference in price.

[dcains]

You can definitely use one of the later 90-amp alternators without the rubber bushings. I've got one on my '85.

[parlant]

Thanks Dcains, really appreciate it!!!

[DesktopDave]

Yep, it's that easy. All the mounts are in exactly the same places and use the same size bolts. Even the battery studs use the same rubber covers. I did the same thing on mine but used a spare 80A unit from an '85 325e. They're very similar units, it's a direct swap.

I was surprised to learn that BMW used a few sizes of M30 alternator pulleys. Offhand I recall that the early cars (M90, B32, Euro B34) had a smaller alt pulley. An overdriven alternator is more efficient: less parasitic drag and slightly more power since it's spinning faster at all given engine speeds. Downsides are a shorter lifespan. I'll see if I can't get some type of picture or measurement for you.

I'm sure you're aware, but avoid the >'88 B35 alternator. It's a really nice 140A unit but the case is totally different. It even uses a completely different engine mount.

I had a pretty similar problem on my old '81. I cleaned the grounds but that didn't fix the problem. Turned out that the gauge cluster bulb holder had an intermittent contact; I bent the bulb holder contact gently & cleaned the gauge circuit board contacts. I also replaced the (original?) bulb since early E24s won't charge the battery if it's burned-out.

[parlant]

Hi DesktopDave. Thanks for sharing your advice!

[Dash01]

Before replacing the whole alternator, try a new voltage regulator, as the brushes on your old unit may be worn. Very cheap and easy fix.

[parlant]

Yes, I bought an original Bosch unit and coincidentally went to replace it this morning. However, although a theoretically easy job, the right side screw of the VR has the oil filter canister right behind it, which makes it pretty damn hard to unscrew as a traditional screwdriver's long axis does not give it enough angle. I even tried with a slightly pivoting adapter and still found it pretty difficult. The current VR installed, although a Bosch unit, is not original to the alternator, I looked it up online and it's a Renault VR--it's a bit bulkier maybe that's why I'm having a hard time unscrewing it.

[dcains]

It is bit tricky to get those two VR screws out. I use a screwdriver bit in my 1/4" socket. Don't worry about which car the new VR is referenced to, as theyre really all the same.

[parlant]

Hi Dcains,
Problem is, if it’s not the proper VR, as much as it does its job, it cannot regulate the load in a timely enough manner so as not to resort to the battery, occasion in which the battery light flickers and the whole system tilts a bit—engine almost stalls, and everything goes a little screwy. Will bring in my mechanic, with more experienced hands than mine, to replace the VR and hopefully a new alternator won’t be needed.
thanks!

[carsnplanes]

VR is easy to replace and to get the screw you mention, you just have to loosen the belt adjusting screws and loosen/rotate the alternator towards the engine.
regulator BMW.jpg
I was measuring a less than optimal voltage of 14.2 volts. it was about a volt low and may not have been keeping my batt charged. With all lights on, blower and wipers, I was measuring about 13.1 and was dropping down to 12.5 at the lowest. I figured it was the regulator and was the fastest and cheapest change i wanted to do first. No, i wasn't getting any flickering charge light, as it never dropped below 12volts. You could throw a meter on the battery while the engine is running and see exactly what it's reading so you'll know exactly. Wait for the light to flicker and measure at that moment and see what the numbers are. You can see the difference between worn and new brushes. Proper charge voltage should be reading between 13.8 and 14.2.
Reading after I replaced regulator:
volt regulator after reading.jpg

[dcains]

You're correct about what the optimal voltage should be, and I can observe mine on an in-dash meter I installed. I can't imagine why your regulator is making voltage that low, as it won't charge a battery like that in any car.

[parlant]

Hi guys,
I replaced the voltage regulator. Car seems a bit better but I suspect the real culprit of the flickering battery light when things are turned on/when revs drop to idle, is the air slide valve. If not that, the alternator itself, as the problem persists.

I still have an electric load problem: if I turn on the lights and then try to turn on the radio, the Becker display goes screwy and there is no sound, instrument panel indicators, especially fuel gauge, twitches. If I turn the lights off and then attempt to turn on the radio, it works fine. Alternator problem or a short somewhere?

[carsnplanes]

Hi guys,
I replaced the voltage regulator. Car seems a bit better but I suspect the real culprit of the flickering battery light when things are turned on/when revs drop to idle, is the air slide valve. If not that, the alternator itself, as the problem persists.

I still have an electric load problem: if I turn on the lights and then try to turn on the radio, the Becker display goes screwy and there is no sound, instrument panel indicators, especially fuel gauge, twitches. If I turn the lights off and then attempt to turn on the radio, it works fine. Alternator problem or a short somewhere?

What are you reading (voltage), when you probe the battery terminals, loaded and unloaded? Just need to know a number, especially when the dash is twitching and flickering, radio not turning on, and when it's not. Feedback please.

[parlant]

Hello,

Sorry for for the late reply. Been traveling for work for the past 2 weeks. Finally had chance to spend some time with the shark.

on the multimeter:
12.39 volts with the engine off for over 2 weeks
12.29 volts at cold idle
11.86 volts with lights on
11.76 volts with lights and high beams on

[dcains]

Pull the voltage regulator and substitute another, if you can. The alternator is clearly not charging at all, and the VR is always the most likely failure. Charging voltage should be 14-14.5V.


Engine/alternator COLD


Engine/a;ternator HOT


Engine OFF

[parlant]

Thanks Dcains.
I changed the VR about 1 month ago. Bosch original unit.
thanks

[dcains]

Time too change the alternator.

[parlant]

Unfortunately the later Bosch 90Amp model alternator does not fit: the pulley goes forward way too much and becomes misaligned with the engine pulley. The belt gets diagonal by 1/3 of an inch. If I turn on the engine the belt will probably escape the pulley.

Are the pulley and alternator fan from the later model alternator slimmer so as to align properly?

[parlant]

Per my previous post above, I upgraded from the Bosch AL46X (80 amp) to the AL49X (90 amp) and maintained the alternator fan and pulley from the first one. Does the alternator fan and the pulley change too for the 90amp alternator? As demonstrated in the photo, the pulley is way too forward so the belt is diagonal. There is no adjustment for this besides changing the pulley and fan as a way to bring it back a bit but I don't know whether these parts change too. If they don't, I have to buy a new 80 amp AL46X and return the AL49X.
20171202_120849.jpg

20171202_120659.jpg

20171125_183709.jpg

[bmw6fan]

Can you flip that pully over?

[dcains]

Mine isn't like that - this is the one I bought:

https://www.napaonline.com/en/p/RSE2138239

It's a Bosch, but not rebuilt by Bosch. In terms of one that is rebuilt by Bosch, NAPA shows the AL48x, which comes without a pulley.

[parlant]

The one I bought also came without the pulley so I used the original one, which is a 2-piece pulley and a “closed” alternator fan, per the photo. I’m hoping that the one-piece pulley and an “open” fan will slim it down so as to align with the belt.

[parlant]

The one I bought also came without the pulley so I used the original one, which is a 2-piece pulley and a “closed” alternator fan, per the photo in my previous post. I’m hoping that the one-piece pulley and an “open” fan will slim it down so as to align with the belt, such as the ones on the photo below.

A123117189839121801-pfand-Exch.-alternator-90A-for-628-CSI+633-CSI+635-CSI-up-to-04-1981,-633-CS.jpg