"burning fan belt"

[pmansson]

Why does a 6 month old fan belt break? Car in question is an XK150 with a Hi Torque 4.2 engine with twin HD8 carbs, built by CMC. The car has done 1300
miles since rebuild, hence still being run in. This morning?s drive was fine, but this afternoon I heard an odd noise when driving off. Fortunately I didn?t get very far from home before I had an alarming noise and fumes looking like they came from the wiring behind the dash board. Got back home within 3 mins and with the bonnet open, saw that the fan belt was missing. Took another car and found it 1.4 km from home (small country roads). Why does this happen.....?

[paulsco]

Are your pulleys out of alignment?

The belt would wear on the edges and eventually fail.

Paul

[pmansson]

Sure it will, but this car and fan belt has done about 40 drives in 2 months, since the engine rebuild, and done less than 1500 miles......

[PeterCrespin]

The bad news is that it sounds like a very unusual failure. The good news is that therefore it should have an obvious cause. Look more closely and try turning the pulleys by hand to check for binding and look for asymmetric wear marks in the grooves?

[christopher storey]

Check for either seized dynamo/alternator or water pump, as Peter suggests. The unusual noise ( was it squealing ) and even more so the smell suggest either a very loose belt ( unlikely to make it smell ) or a seizure of some kind
( very likely to make it smell )

[pmansson]

Thanks to Christopher and others for advice. Yes, the alternator had stuck, because one of its 3 very long screws had come undone and moved out and blocked the entire mechanism. Can?t see the make of it but it appears to have an internal regulator. Not the Lucas 11 that I have on another Jaguar. Problem is that none of my large selection of sockets will go into the opening far enough to fully tighten it. While I wait for a new belt, I will first of all determine the size of the screw and then Loctite it when I find a suitable socket. Looks proprietary Lucas? to me. Perhaps the entire alternator has been damaged in the process. The pulley doesn?t spin like a roulette wheel at any rate.
Why do these screws come undone on a new alternator....?
Peder

[PeterCrespin]

The pulley doesn?t spin like a roulette wheel at any rate.
Why do these screws come undone on a new alternator....?
Peder

Can't say I'm sufficiently familiar with casinos to know how a roulette wheel spins, but you could remove the belt from one of your other Jags to compare? Perhaps there is one being worked on at your place? I got turned away from the Monte Carlo casino for wearing my motorcycle jacket. Then when I gave it to my young wife after she'd been inside, the doorman decided he didn't like my footwear. So we wandered across the street to the Cafe De Paris and got shooed away for looking in the windows!

As for the 'Why?' question, who can say? One soon learns with young children that after ten follow-up 'Yes, but why?' enquiries (by which time one is approaching existential 'meaning-of-life' questions) the simplest answer is to say 'Just because.'

Perhaps the builder had a screw loose? On the other hand, perhaps he was thinking about his wife in the French Maid outfit he'd just bought for her birthday? On ne sait jamais.

[malcolm]

I went through dozens of belts on a boat engine in this fashion, after a new alternator had been fitted. Looked in perfect alignement, but eventually discovered that the replacement alternator was about 1 mm different in bracket depth, and was enough to wear out belts at a fast rate of knots. Tiny bit of grinding off and all was well.

[Heuer]

Belts normally snap due to age as the rubber cracks which can be easily seen by turning it inside out. If the pulleys are out of line the belt will begin to flay and you have advance notice because of the noise of the cotton strands whipping against the car. If the belt becomes contaminated with oil it will begin to disintegrate fairly quickly and you will again get a warning by the flaying cotton. A seized alternator will usually cause a squealing sound accompanied by the smell of burning rubber.