A long post here, which might be of interest to anyone with alternator problems.
Part One – The Problem - Friday
I thought I would round off 2010 by treating my 1988 3.5 EFI Vogue SE Auto to a wash after its last pay and play day a couple of weeks ago. It had been working fine since then.
I gave it a hosing under the bonnet, not deliberately directing the jet on the alternator, but it did get wet.
I then turned the car round and noticed the ignition warning light flash briefly, but thought nothing of it until I parked the car back on the drive and a harsh grinding noise started. On investigation this was coming from the alternator. It sounded like something was stuck inside and had been caught between the rotating and static parts. Also the rev counter does not work until the engine is reved a bit and the ignition warning light is glowing until revs are increased. Sometimes the noise will come and go instantly i.e. not start gradually or fade away. Other times when I start the car there is no noise for a few seconds and then it starts when revs are increased.
I replaced the regulator, brushes, slip rings and rectifier in November and all had been working perfectly until today.
So I stripped the alternator down and found no signs of any parts rubbing against each other, or other damage. No mud inside anywhere near the working parts, and the brushes and slip rings are fine. While I had it apart I put new bearings in, just in case one of them had been damaged somehow. So I have had a good look at every component from all angles, and when reassembled the shaft spins as smooth as silk.
All to no avail - when I put it back on the car the noise was just as bad.
I also tried running the car without the alternator drive belt in case the noise was coming from an adjacent component like the power steering pump, but the noise stopped.
I had done nothing to the car today apart from hosing under the bonnet - could this have damaged the rectifier? If so I could understand the symptoms, apart from the noise.
Part Two – The Solution - Today
I started the car again today and unlike Friday, this time there was no life from the alternator at all (last time it would work if I rev'd up), and no noise!
So on the basis that I had replaced everything else in the alternator recently, that only left the coils to check. A few minutes with the multimeter confirmed that there was indeed a short from the wires in the field (static) coil to the frame.
So, the problem was identified but where was the fault? I gave the coil a good clean with a toothbrush and warm water to get the mud off (not a lot really, it was dirty rather than caked with mud) so that I could see what was what.
The only place I could see a possible fault was on one of the wires where it looped round into one of the slots in the frame - it looked like there was a little bit of spark damage. It wasn't easy to see because it wasn't the top wire, and all the wires were hidden under one of those cardboard(?) inserts which hold the wires in some of the slots.
On the basis that I had nothing to lose, I thought I would have a go at a repair, although to be perfectly honest I didn't hold out much hope.
So, the first step was to very gently prise out the cardboard so that I could get at the wires, and then one by one lift them out of the slot so that I could examine them. The 5th wire was missing it laquer and it looks like the insulation had broken down just on the cormer of the slot where the wire pressed against it, thus causing the short to the frame.
I then painted the wires with nail varnish in the hope that this would repair/maintain the insulation, and then lay insulating tape between the first three wires which I pressed back into the slot. I didn't bother with tape between the remaining wires because the lacquer on them seemed OK, and there wouldn't be room in the slot for that many layers. Even then it was touch and go that everything would fit back in. There is very little clearance between the field coil and the rotor, so everything needed to be flush.
As the wires had been bent outwards when I lifted them out of the slot, I had to hold them in place with small cable ties, for which there was just enough room.
After a few reassemblies, I was happy that I had everything fitted correctly and that the surplus edges of the insulating tape were trimmed back enough to avoid any rubbing.
I then refitted the alternator to the car (I am getting quick at this!) and started it up. At first I though it hadn't worked because the ignition warning light didn't go out, and the rev counter didn't function. After a few seconds both returned to normal, and were fine on subsequent restarts. The grinding noise has also gone, so it looks like this was generated by the short somehow!
It remains to be seen whether this will be a permanent repair, and I do wonder whether the water was the cause or whether this was just a coincidence.
Anyway, I have gone into some detail here in the hope that this might help someone else. It's just a shame that this problem prevented me from going to Sibbertoft for Pay & Play today!
Happy New Year everyone!
Pete