MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Squealing Alternator

Hi again,

I have an alternator that makes the fanbelt squeal. Same make (Lucas), same size, same distances, tensions etc. etc. I've measured up and swapped everything a number of times, on the same engine (brackets unmoved).

The only thing I can't measure accurately is the V form of the alternator pulley. Can one pulley be a narrower V than the other and thus cause the squealing.

Or any other thoughts?

Ta,

Iwan
IA Jones

Water Pump?
Pat Gregory

Pour a little water over the belt with the engine running. If the noise stops its the belt, if it does not its the w/pump, alternator etc.
Denis
D M Hill

If the belt and pullies are correct then you can get some proper stuff to spray on the belt/pulley to stop the squeal or try a very little spray WD40 (normally I don't recommend the stuff).

Where a water pump makes a noise I've also as a first try sprayed some WD40 on the pump shaft, my thought is it might wash out a bit of grit or give just a little lubrication, if it works fine if it doesn't you'll probably be replacing the pump anyway, and it has worked previously. Same with whining alternator shaft, a little spray, if it works great, if not no great loss.


Nigel Atkins

Iwan
It's probably caused by getting some oil or something on the belt when fitting the new alternator--Putting WD40 on it will make it slip worse and probably get into the belt and wreck it-it will be quiet,,but slipping
You could try some contact cleaner on it, just give it a good wet squirt while at idle
Is the alt. pulley the same diameter as the old one, if it's smaller it 'could' be a cause
Is the belt tensioned up nice and tight, alternators like them tighter than generators as they work harder at lower revs compared
willy
William Revit

Sorry,

I did not make myself clear. The alternator that is in the vehicle at moment is ok. When I swap it out with the other one I get squealing on the belt only. Positioning (re: backwards or forwards adjustment) of both alternators on the engine brackets exactly is the same. Both pulley centres are 31mm (in front) from the alternator housing and line up with the water pump pulley. I have measured up the position of the alternator out along the adjusting arm (from the engine) to make sure its the same, put the belts at various tensions and tried with 3 different belts. No noise from pulleys water pump etc..

I then swap out the alternator, same position, same tension - everything the same and the belt squeals (and over-heats). Have tried various tensions.

The only thing I'm thinking that is left is a narrower v groove in the pulley. Have not swapped alternator pulleys yet.

Ta,

Iwan
IA Jones

Iwan,
to me your theory seem likely.

Willy,
I've never sprayed WD40 on a fan belt but thought a very little would be OK as there seems to be very little to WD40, its very overrated (and not the brand name on all sorts of sprays is forcing out better makes).

Perhaps, as often, I've remembered wrong but I thought I'd heard of others doing so without poor outcome - but I could be wrong.

I've got a spare fan belt I could try a prolonged soak test with WD40 - but I haven't got any WD40.
Nigel Atkins

Based on what Iwan has done already I don't think WD40 will help long term.

Swapping the pulleys over seems the obvious next step, but getting the nut undone can be tricky. Wrap the belt round the pulley and grip it as firmly as you can, and use an impact gun on the nut. Maybe clamping the belt in a vice if you are prepared to sacrifice it.

If you have Plasticine or similar you could try pressing it into the 'quiet' pulley to get the profile then comparing it with the 'noisy' pulley, and/or vice-versa. Whatever material you use needs to be stiff, and not sticky.
paulh4

Paul, maybe not but like Dennis's method it might locate the source of the noise if it stops the noise if only for a short time.

Twice it's worked on water pump shafts that weren't replaced during several years of ownership, IIRC one was on my mate's RV8 engined TVR which I think he had for 3 years.

I had the same thoughts as you about swapping the pullies to see and the potential hassle if tried but Iwan seems up for effort. I've only done it once and totally against my usual luck I got the nut off reasonably easily so I'll never push my luck by trying again unless I really have to plus I can't remember what method I used.
Nigel Atkins

From what Iwan said this morning I got the impression that changing just the alternator brought the noise on, implying it must be the different pulley that is causing the problem. Yes it could be the alternator itself that is squealing, but then he says the belt is getting hot with the squeal as well. That - and the noise - could be down to a partially seized alternator, but surely while swapping them that would be obvious.

That does leave one possibility, and that is an electrical fault inside the alternator i.e. a short circuit which is putting a heavy load on the belt when the alternator is charging. More difficult to determine, except perhaps by measuring system voltage with minimal electrical load, and maximum electrical load.
paulh4

My enjoyment would be with one working alternator fitted to the car, I'd leave the 'pleasure' of finding out what's wrong with the other to anyone that wanted to take it off my hands for free, I like to recycle but not my own pain, I've had enough of alternators, I just want a fully charged battery and a car that starts easily and runs well.
Nigel Atkins

Hi,

The alternator was going to be a spare. I have spares for everything. Yes, even spares for the spares!

I'm going to pull the pulley when I get a chance and report back. I'm almost certain that it's nothing to do with a malfunction within the alternator.

Ta,

Iwan

IA Jones

I'm with Iwan there, if I have spare I like to know it works, and that includes test-fitting a fan-belt bought as a spare. No point in carrying something if it's not going to work.
paulh4

Paul, excellent idea, when you test fit something like a spare fan belt then make sure it's new and if the test fit is successful leave it on and keep the previously fitted fan belt as a spare.

Provided parts are changed before they become decrepit and the new parts tested for reliability for a reasonable period I can't see the point of carrying all these spares.

I carried the previous fitted fan belt as a spare in the boot once as it took up next to no space but then didn't bother as in my entire life I've never known anyone have a fan belt failure.

I have heard of people being struck by lightening so my boot is full of protective clothing ready for if I should travel through a storm.
Nigel Atkins

I do put my 'old' belt back on, working on the principle that as it has an unknown amount of life left if I kept it as a spare then it could fail an hour after refitting!

The only belt failure I've had was shortly after purchasing a Reliant Scimitar. On the M6 round Birmingham, and before I could pull across to the hard shoulder in peak traffic it had boiled the coolant out. Called the AA, he tried all his belts and they were either too big or too small, apparently there were a dozen or so for that engine (Frord Essex) over the years. He called up the spares van - ditto, so another van was called up. Eventually there were about five vans and none of them had one that fitted. Then I had an idea, that if I removed the adjuster bolt altogether, it would allow the alternator to get that little bit closer to the engine ... and the first belt then just went on! After that I've always carried a spare.
paulh4

I'm a bit lost with your first sentence, unless you mean you buy two new belts and test fit them both and keep one as a spare knowing that it's new and fits. A very good idea if you're going to be traveling in a area where you can't get spares. Otherwise it means a perfectly good belt sits in the boot doing nothing for years, waiting its turn. My thought is replace the existing belt before the end of it's useful life that way you lessen the chances of it breaking whilst in original use and as a, presumably emergency, spare you know it fits and has sufficient life in it to get you home.

With the Scimitar the car was new to you so with a belt of probably unknown age and treatment and before you had the thought to check or change it (or possibly before you had the experiences not to trust what previous owners had done with the vehicle). I'm sure now you'd change many parts and do a full service when getting a s/h car that was new to you.

I'm surprised you didn't carry one of those multi-fit emergency fan belts, remember them(?), IIRC(?) the one I saw was a red-coloured, thick walled round hose that you cut to size and joined by some metal insert, possibly AA brand too - or am I dreaming again.

Nigel Atkins

Take existing belt off, test fit new belt, refit original belt, put new belt in boot. And yes, the new belt sits in the boot for years - Sod's Law i.e. 30 years in the roadster along with the spare inner tube, and 24 in the V8. I'd rather keep a new belt in the boot than a used one of unknown condition.

If you change stuff of unknown condition on a 'new to you' car where do you stop? You said yourself you have never known anyone to have one fail. That's the point of getting a spare when you get the car and is the benefit of hindsight. As for everything else when something fails or gives cause for concern you change it then. The same car had one hose fail, then another, and when the third one failed I changed all the rest along with it, it had about ten as I recall. That car hadn't been looked after, and it was about a year before I had any confidence that a long journey wouldn't result in some kind of problem. Having said that, the belt failure was the only time I've called out the AA in 50 years.

I remember those so-called multi-fit belts, I also remember the comments that they didn't last five minutes.
paulh4

Yeah it's all about the law of averages, Sod's Law, logical and illogical beliefs and experiences.

I was thinking that the used belt would be one that you'd fitted so know the age and use of, so you know it still has good life in it for use as an emergency spare, an unknown belt I'd check and change, probably sooner than later.

If the multi-fit belts were as I remember I can't/couldn't see how they'd even last 5 minutes.

A belt is small and light item whether stored in a boot, shed, garage (for those that have such things) but items like alternators are bulky and very heavy but if you have the space and inclination then fair enough.

Nigel Atkins

Just wondering, Iwan is fitting both alternators at the measured same point from engine on the arm. If the diameter of the replacement pully where the inner belt surface runs is slightly larger than that on the replaced alternator/pully, it would stress the belt more and possibly be a cause of noise and, significantly, heat.

I'd be inclined to measure both pully dimensions at that point. If the same than at least a possible cause would be eliminated.

Regards
Roger
R Taylor

Fair point, I got the impression it was only the v form of the pullies that hadn't been measured but better to ask than assume.

We await Iwan results, personally I like to hear the conclusion - but can rarely remember what it was.
Nigel Atkins

Hi Roger,

Have tried the squeaking alternator at a number of tensions (i.e. slight differences in distance along the arm) - not a fixed distance. Also, the diameter of the pulley is the same, have not measured the internal diam. of the v-groove.

Ta,

Iwan
IA Jones

I recently had the slippng/squealing fanbelt problem on my MGA which has a 5-brg engine and an alternator.

The squealing was getting worse and worse even though we tightened up the belt a couple of times. Eventually the squealing become so bad that we could smell the rubber of the fanbelt burning and re tightening the belt made no difference.

So I fitted a new belt ( I would have fitted it sooner but I found that the spare belt which I had carried in the car for 6 or 7 years was actually too short to fit and I had to order a longer one.

When fitting the new belt I spun the alternator by hand and it seemed to spin easily with no bearing noise.

The new belt seemed to mostly cure the squeal but I heard it again briefly on a long motorway run at around 70 mph (3500 rpm.
This was accompanied by the weird sight of the rev counter needle dancing all over the dial between zero and 7000 rpm.

So I assumed that what was happening was that the alternator was partially seizing up under load causing the voltage output to fluctuate.

I have since then replaced the alternator and all seem to back to normal.

The removed alternator still spins freely.

Has anyone elso had this happen?

Cheers
Colyn
Colyn Firth

Ooops, hence my practice of trial-fitting spare belts.

System voltage shouldn't have any effect on the tachometer unless it drops way below battery voltage. If the alternator stops spinning it effectively disconnects itself from the system because of the output diodes, as it does when the engine stops for any reason. Only if the alternator diodes are faulty would it try to short the battery to earth, which burns the wiring.

I suspect the tachometer action was something completely different, especially if it didn't happen with the original badly squealing belt. If you are doing 3500rpm and cut the power or signal to the tach, then it will suddenly drop to zero. Then when the power or signal is reconnected at 3500rpm the needle will go way past 3500 initially as it rises very rapidly and overshoots, then falls back.
paulh4

This thread was discussed between 02/08/2018 and 09/08/2018

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now