Grumbling, growling alternator.

WarrenL

WarrenL

Active Member
The other day I tracked the source of grumbling bear sound in the engine bay. Unexpectedly, it was the 11AC alternator, which I fitted with new bearings only quite recently. The culprit was the small closed-end needle roller bearing, bearing (get it?) the number BCE89.

- If I hold that half of the housing, sit the rotor shaft in the needle roller bearing and spin the rotor, there is quite a noise, and the housing vibrates unpleasantly in my hand.

- If I push out the needle roller bearing and place it over the end of the rotor shaft and turn it back and forth with my fingers, it feels a little notchy but not dramatically so.

- The rotor shaft shows some pitting, extending back as far as 4mm from the end of the shaft, however the next few millimetres of shaft length are smooth and show no visible sign of wear.

So, has this rather new bearing worn out, and could those 4 millimetres of pitting have something to do with it? If so, then simply putting in a new bearing is going to result in the same outcome in a few months time, so how would you advise me to proceed?
 
Sounds like the shaft is the cause of the bearing failure, Warren. So that'll be a new alternator then. Bother, Just when you're skint from everything else.

So now decision time looms. Do you want to keep it looking standard under there, in which case sourcing a replacement 11AC looms. Or are you prepared to do a bit of updatin? In which case you need the later alternator bracket - which pushes the alternator out clear of the cam cover - and a modern Range Rover or similar alternator. These are quite cheap on Ebay from all sorts of sources with all sorts of power outputs up to as high as 130A. They have the secondary advantage that you can abandon the regulator under the passenger shin bin and have everything integral on the end of the alternator. The mod is a pretty standard one, so we can all help with the wiring change if you go this route.

Chris
 
I fear you're right, Chris. Pain in the arse right now, but that's the way the cookie crumbles. A bearing is only a few dollars though, so for now I'm going to stick a new one in, pack it with moly grease and hope that the previous one was duff, or perhaps I managed to get crap in it during installation. It'll buy me time, if nothing else. Alternators are easy to pull out and put in.
 
Well, I gambled and lost. A new bearing and the racket from the spinning rotor is still the same. However, this is still with the half-housing sitting on the palm of my hand, and the other hand spinning the rotor. Final judgement shall be passed when I actually bolt the alternator together and the rotor shaft is held correctly in position by front and rear bearings.

Is it possible that a worn rotor shaft could cause such a noise?
 
Update: problem located.

Curious indeed! By borrowing a friend's spare alternator and swapping bits around in a process of elimination, I've tracked the source of the racket to the rear alternator casing. I can't explain why it would be so, but if I put my friend's rear casing on (complete with cruddy old bearing), the noise disappears. As soon as I reattach my own rear casing (with a choice of bearing; old, new, or cruddy from my mate's casing), the racket reappears. I repeat, the only thing that I change in this experiment is the rear casting. I even swap over the brush box etc to make sure that the one and only variable is the casting.

There is nothing visually amiss with my rear casing, but something must be distorted or misaligned, or invisibly cracked, or something. Any metallurgists about who might care to shed some light on this mysterious affliction?
 
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