Fan belt/alternator problem

blue beasty said:

Check alinement of pulleys and for play in the bearings. He should be able to adjust to the right tension, which might need to be more than normal to spin the oversize alt to avoid slipping.

I assume they know a new belt will need re-adjusting after a few days due to intial stretch?

Is that oil splatter on the chassis? Is power steering fluid getting on the belt?

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gse1986 said:

The belt needs to be tight, otherwise it probably would shred.....the haynes manual says something like 0.5mm of slack for every 10mm of belt i think, or something to that effect.

I got someone to tighten the bolts while i was pushing the alternator, and that worked fine for me.

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JonnyP said:

I am asking this on behalf of a mate of mine who has an uprated alternator (130 amp) in his 90 (200tdi). His fan belt keeps shredding.
He thinks its something to do with the alternator, because it never used to shred belts as standard, but also to do with the slack in the belt between the two pulleys, where I am pointing in the picture.
He would like to know if some sort of tensioner can be bought or made to fit in there to help stop the belt moving about
Or is the alternator just too powerful..?

Anyone know about such things..?

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discomania said:

Does he have increased electrical load that the 130A alternator was installed for?

As said previously, check the pulleys are all in correct alignment first.

That alternator alone will put a load of over 2HP onto that belt if it was loaded up. Consider that, that is a fair bit of tension to put on a small belt.

The proper tension of the belt, is the lowest tension at which it will not slip at peak-load conditions, however as the engine is variable speed, it must be tensioned slightly more to allow for increase slip possibilities during quick increase or decrease in engine revs.

Over tensioned belts will generate heat which can cause them to stretch, which then leads to the belt probably being under tensioned...

Under tensioned belts will slip leading to more heat, which will damage the belt, from the looks of the black marks on the chassis it looks like the belt is throwing a fine rubber dust, often a sign of heat wear.

I would talk to a belt supplier, give them the dimensions of the belt and see what they can do, they will almost certainly have an uprated version. Look for a belt designed for increased power and torque and one that has good dynamic balancing; that is it's ability to stay true even if the belt is being diverted in such a way it may not run straight and flat.

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discomania said:

Magneti Marelli, Bosch etc... these are all good alt's.

Try Tom at CCW tools, phone him up, they do great alternators and starters at good prices. I wouldn't buy an alt or starter from anywhere else now.

Bearing change is not bad, again, get onto a local engineering suppliers and get a bearing of the right dimensions but uprated. I do this with bearings I replace, if it needs to be rated to 20,000rpm I will get one rated at 50,000 etc. See if you can get a fully sealed bearing too, they withstand the wet better.

Tell him to call his local Brammer and ask about bearings and belts. Or if you give me the dimensions of the belt I'll get you a Brammer code for it.

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