Splitting an Alternator - How?

[James76G]

This is the Bosch alternator from my 1992 E36 325i



It came out of the car relatively easily despite it having been there 30 years and it was working fine electrically but the bearings were very noisy. So my plan was to take it apart, replaces the bearings, tidy things up and reinstall it.

I've removed the end cap, regulator and the 4 case screws so in theory the two halves should now come apart. Well according to all the YouTube videos I've watched anyway.



But it just isn't happening. It's moved about 5mm and now it won't budge. I've used screwdrivers, cold chisel, punches and various hammers with no joy. So clearly something isn't right and I've already taken a small chunk out of the case.




So, has anybody got any tips on what to do next and/or differently. Obviously I could buy a new one, but they seem expensive and hard to source so I'd rather not if I can help it.

[GreenV8S]

I expect the brushes will be holding one end. If either of the bearings is tight you might need to tap that out too.

[Polly Grigora]

Refit the 4 through bolts by a few threads (5 or 6 turns in, you don't want to be trashing the threads) and hammer their heads while holding the slip-ring end shield

If the through bolts aren't long enough to give a good distance for knocking their heads through flush to the end shield, fit some longer bolts and hit their heads

All the above achieves is to allow the slip-ring end shield to be driven off the slip-ring end bearing of the rotor as they are a tight fit

You are punching the drive end shield, rotor and its slip-ring end bearing away from and out of the slip-ring end shield by bashing like fk at the bolts rather than trying to prise the end shields apart

Don't worry about small damage already caused to the casing

Once the shields are coming apart by a few mm you might need to prise or knock the stator out of the drive end shield, the stator must come away with the slip-ring end shield, be careful when prising the stator as you don't want to be shoving a lever into its windings

The final separation can be achieved by prising between brackets at their strongest points where the through bolts go through @ 180 degrees apart with two levers



Check all corroded joints

Edited by Polly Grigora on Saturday 30th July 16:49

[James76G]

GreenV8S said:

I expect the brushes will be holding one end. If either of the bearings is tight you might need to tap that out too.

Brushes are already out as they integral with the regulator so corrosion holding this one together I think.

[James76G]

Polly Grigora said:

Refit the 4 through bolts by a few threads (5 or 6 turns in, you don't want to be trashing the threads) and hammer their heads while holding the slip-ring end shield

If the through bolts aren't long enough to give a good distance for knocking their heads through flush to the end shield, fit some longer bolts and hit their heads

All the above achieves is to allow the slip-ring end shield to be driven off the slip-ring end bearing of the rotor as they are a tight fit

Thanks, this is a great suggestion so I will give it a go.

Regarding those terminals, it was all working before I pulled it from the car so hopefully they will just need a clean up with some wire wool.

[Polly Grigora]

Great you've returned

Bash one then bash another and so on working around the 4 of them, it never fails, ruthless does come into play, most important part is the stator staying with the slip-ring end shield otherwise the stator leads will break or pull on and break the rectifier

[James76G]

There has been some progress, of sorts.

Using your suggestion of inserting the screws and hitting them I managed to get the front case free. Thanks for the tip.



That meant I could access the front bearing but that required removing the cover holding it and inevitably the screws for that are beginning to round out...

Also I could not remove the rotor at all. From what I can tell there's a bearing on the rotor shaft, then there's a plastic collar and that is an interference fit in to the rear case.

I tried using a punch to tap the bearing and thus free it but there's so little room. I put a nick in plastic to check that was what it was but for whatever reason it just isn't letting go.



While this is on my 2nd car, it's now in the way and I need access to the space it lives in so I have bought a replacement alternator to get it mobile again. But I would love to get this one apart so I can at least have a go at replacing the bearings (which I have already bought)

[Polly Grigora]

Screws need a good screwdriver or socket for no slip-off, a little heat and wd40 may help (don't melt the alloy casing). Pressure on the end of the screwdriver handle also stops slip-off. Cutting slots in the screw heads and using a flat bladed screwdriver can also do the job

If all else fails, drill the heads off the screws, prise the retaining plate off and one at a time grip what's left of the protruding threads in a vice and turn the plate to loosen them off, mole grips will then turn them out of the plate

Shock horror in seeing that the drive end bearing was pushed off the rotor shaft rather than the rotor with slip ring end bearing being pulled out of the slip-ring end shield

You can blame me for the above, I should have told you to leave the pulley on the rotor drive end to prevent the drive end bearing being pushed off the rotor shaft, it doesn't happen often but......Sorry about that

Best to knock the drive end shield back on the rotor, put the pulley back on and bash away again at the through bolts

Am pretty sure that the plastic you mention is the bearing grease seal, it's a fully enclosed bearing

You might find that the slip ring is bigger than the inner diameter of the bearing and if so it will need removing before pulling the bearing off. If the slip ring does need removing it's a bin job, a new slip ring is needed and that would need skimmimg in a lathe after pressing it on the shaft and soldering it

Out of the hundreds of alternators that I've had dealings with, approximately 20% of the slip ring end bearings were good enough to go again even though they were replaced, the drive end bearing takes most of the punishment

Edited by Polly Grigora on Sunday 7th August 16:44

[GreenV8S]

Polly Grigora said:

wd40 may help

Proper penetrating / easing oil is far more effective at freeing stuck fasteners.