Noisy Alternator?

The other evening just after starting and putting the lights on I got a nasty noise from the engine compartment. A mix of auxiliary belt slip and a metallic grating that rose with revs. I sat contemplating going to get my other car for around a minute or less when the sound stopped dead and hasn't come back so far. The belt was new around 1K miles ago.

Any ideas? I thought the bearing in the alternator had gone but a worn bearing wouldn't instantly silence itself in my experience.

2004 TF.

I have experienced the exact same thing, normally on start up after turning on lights and putting the electrical system under load. A load squealing noise which eventually goes after one or two minutes. My belts have not been touched since I bought the car a year ago!

As you will not require me to tell you, the squawk is the belt slipping on one of the pulleys, generally the alternator & is either due to incorrect tension, excessive current being drawn or a combination of both. There’ll be an ideal tension for the belt in figures layed down in the manual, but I’ve always set mine & this goes throughout my car history to “that feels about right” & it usually is.
As the belt pulls tight against the shaft & thus the bearing, the balls in the “slack side” of the race can dance within the race cage, don’t forget that these aren’t the highest quality bearing & can produce a sound similar to a bearing close to failure. As soon as the load is reduced all systems return to normal.
A bearing made to closer tolerance & greased will very rarely exhibit this aspect.
I would like to thank my son Edward for this, he spent ages tracking the problem as described with a Kubota tractor he had through his workshop.
Tah Ed.

As a possible useful addendum to this. When I first got my MGTF the previous owner informed me it had a new alternator but despite this it had started to slip.
Once I got it all opened up with the wheel off I decided to replace the pulley and belt. I was horrified to discover that despite the garage seemingly fitting and adjusting it. They had a failed to adjust it properly by tightening the fine adjustment screw on the rear of the alternator itself and simply must have done it by slackened slide bolt assy. This is a sure fire reason it slipped back and knackered the pulley and belt. I reassembled and all has been well. The belt did need a retightened
after few hundred miles as per usual methodology but since then been fine. I agree with the methods used to determine this as a motorcyclist and a defection of about 2cm is good for the Goldilocks setting.
My first port of call would be to check this screw to determine if tight or indeed if used at all…

Invest in the rose jointed offering, once your hands have stopped bleeding & A&E have discharged you they are straight forward to adjust, retaining their setting ad infinitum.
Having just said that I had a look in everybody’s favourite rubbish bin (eBay) & couldn’t find a reference, someone will know & clue you in; it’s a long time since I fitted mine.

Airportable wrote:

Invest in the rose jointed offering, once your hands have stopped bleeding & A&E have discharged you they are straight forward to adjust, retaining their setting ad infinitum.
Having just said that I had a look in everybody’s favourite rubbish bin (eBay) & couldn’t find a reference, someone will know & clue you in; it’s a long time since I fitted mine.

The problem with doing this is that there is the possibility of no blood sacrifice being made…..and the car gods always require a blood sacrifice to be appeased, otherwise the car either won’t work or suffer a catastrophic failure soon after! :hgf: :bust:

Airportable wrote:

Invest in the rose jointed offering, once your hands have stopped bleeding & A&E have discharged you they are straight forward to adjust, retaining their setting ad infinitum.
Having just said that I had a look in everybody’s favourite rubbish bin (eBay) & couldn’t find a reference, someone will know & clue you in; it’s a long time since I fitted mine.

These are available here from MG Mania (and possibly others).
I've seen an article somewhere on how to put your own together but I can't remember where.
There is a how-to here on The T Bar and a video on YouTube here.