Help: chewing up belts...

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ifloochies said:
Thanks guys for all the responses...
So I went about checking the alignment, and as far as using the straight edge of a meter rule, it seems to be spot on. The alternator is a 100 amp Bosch unit as seen in some of the RR classics, and it bolted straight on to the seat without modification.
Been motoring around town for some time now with the AC off and so far, the last belt seems to be holding up... Back at home, I turned the AC and lights on as the truck sat in the yard idling, and the first thing I noticed after I turned the engine off was that, the temperature of the alternator belt was bordering on hot.... Could this problem really be related somehow to loading on that poor little belt?
Click to expand...

If the belt is getting hot then I'd check that it's tight enough and stiff enough to not stretch and slip. Aftermarket belts may be variable quality and it might be worth trying a number of different belts .. though to be honest I have a 300 tdi so dunno how hot a 200 alt belt gets ... Does the alternator spin freely when the belt is off it? Any movement in the alt shaft, bearings etc. It should rotate freely with no easily discernible play side to side or front to rear.
 
Just had the charging system checked by an auto-electrician who told me that the problem lies with the pulley of the high-output alternator.
It has a smaller pulley which he explained, is designed to have the alternator run at a greater speed, especially at idle. Problem is, diesel engines have lower idling speeds, coupled to the fact that the speed drops a bit more as its burdened with the load of the AC compressor or any other ancillaries that are turned on.
The electrical load of energizing the clutch of the compressor and running all the other vehicle electrics induces a resistance between the stator and rotor of the alternator which tends to make the belt slip as a result of the smaller contact area on that size of pulley.
He explained that that is what causes the belt to heat up, degrade and finally fail. (I hope I got all of his explanations down right)

So as it turns out, the options left to me are:
1. Increase the idling speed of the engine so the alternator never lags under load. (Not an option because its coupled to an auto box, ZF 4HP 22. I hear they don't like to be treated that way)
2. Change the alternator or try to find a bigger diameter pulley that would fit so the belt has a larger contact area.
3. Change out all the pulleys and have the single serpentine belt and pulleys installed,(if it can be done)
4. Having to do without AC and the in-car entertainment system whiles the car sits idling in traffic (kids would just love that).
Help me out here folks. Didn't think an alternator swap would get so complicated.
 
Theres loads of info out there out split charge systems. If you need some extra power and this alternator issue isn't solved. I would go for the split charge,as you've got AC,a second alternators a no go. With 2 batterys you can put all non improtant things on the second battery.
 
freelance said:
try a better quality belt, one containing kevlar preferably
Click to expand...
:crazy_driver:

said that previously,
go get an engineers supplies shop,
get one size fer size replacement,
one wiv the cuts on the inside to enable tighter radial bends of the belt.

I used to get one fer my race engines, no adjustment, just bottom pulley to water pump pully.

Conventional V-Belts - Belts Sizes A - B - C - D - E Section Belts

or
Belt Size Chart

as a referance guide..

used that Idea on my lawnmowers drive belt...cheeper then original part & so much better.
 
ifloochies said:
Just had the charging system checked by an auto-electrician who told me that the problem lies with the pulley of the high-output alternator.
It has a smaller pulley which he explained, is designed to have the alternator run at a greater speed, especially at idle. Problem is, diesel engines have lower idling speeds, coupled to the fact that the speed drops a bit more as its burdened with the load of the AC compressor or any other ancillaries that are turned on.
The electrical load of energizing the clutch of the compressor and running all the other vehicle electrics induces a resistance between the stator and rotor of the alternator which tends to make the belt slip as a result of the smaller contact area on that size of pulley.
He explained that that is what causes the belt to heat up, degrade and finally fail. (I hope I got all of his explanations down right)

So as it turns out, the options left to me are:
1. Increase the idling speed of the engine so the alternator never lags under load. (Not an option because its coupled to an auto box, ZF 4HP 22. I hear they don't like to be treated that way)
2. Change the alternator or try to find a bigger diameter pulley that would fit so the belt has a larger contact area.
3. Change out all the pulleys and have the single serpentine belt and pulleys installed,(if it can be done)
4. Having to do without AC and the in-car entertainment system whiles the car sits idling in traffic (kids would just love that).
Help me out here folks. Didn't think an alternator swap would get so complicated.
Click to expand...

Now if you put a bigger pully on alt it will spin slower . To make it spin faster at tickover it would need a smaller pully . But that would make your problem worse.
Now did the auto electrician just stick a meter on to check the charging volts. Or did he check the current loading as well.
With various electric items off and on .

For say a diesel with mechanical pump no ecu .ect and lights off heater fan off rear demister off radio off . There shoud be very little load on the alt. So its easy to turn only when the load comes on will it be harder to turn .also diff altenators will give diff outputs at different rpm . Engines that run at a lower rpm have an alt that gives max amp at lower rpm than and engine that runs at a high rpm which would have a alt that only give max amp at the higher rpm. Which is usually done with the pully.
Did he check the actual alt rpm v engine rpm so you can work out the pully ratios.

Or the ratio can be worked out crank pully divided by alt pully.
A 6 inch crank and a 2.3 inch alt will give ratio of 2.61x engine rpm 700 equals a alt rpm of 1828
 
Last edited:
Is the problem alt on a belt of it's own?

I wonder whether, if you can't find a smaller pulley for the alt, what about changing the driving pulley for a larger one? That would speed up the alt, hopefully enough to get it working at tickover.

As it's not standard, I think I'd measure the centre to centre of the driving and driven pulleys, then go to an engineering suppliers and see what pulleys/belts combinations they can come up with that have a higher ratio than you have now.
 
Hello folks,
Just returned from a long roadtrip with the Disco,(7086.1 on the clock) and I'm happy to report that it was all done on that one alternator belt I left home with.
It turns out swapping the small pulley with the one from the stock alternator did the trick afterall. Only thing is now, from start up, I've had to accelerate a bit off idle to get the battery charge lamp to go out.
It seems that small variance in size between the two pulleys makes a lot of difference. Aside that, I cant see what else it could have been that consumed 9 belts in 2 weeks.
Anyway, all that matters is that we got the problem solved before it drove me nuts... thanks for all the contributions guys
 
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