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Old 15-04-2017   #1
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auxiliary belt idler

For over a year now the 1.9JTD engine on my 2004 bug has been rough but non metallic. It is obvious where the noise comes from and it can be seen when the plastic wheel-arch cover is removed. It is from the auxiliary belt idler - when you look at the idler it is moving up and down a lot with the belt . I replaced this about 6 months ago and the noise subsided a little, but it wasn't a cure.
I took a tyre in for a puncture repair and the fitter standing next to it said. 'I recognise that noise - it is a seized one-way bearing on the alternator'
I know of no such bearing and he isn't a Fiat man but perhaps someone can confirm or suggest a remedy. It isn't the crankshaft pulley and we never use the air-conditioning so I presume that pulley doesn't engage.
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Old 15-04-2017   #2
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Re: auxiliary belt idler

I can confirm that the pulley on the alternator can have a one way freewheel mechanism to reduce load on the drive belt.
The free wheel direction is the normal direction of rotation of the alternator pulley.
These one directional pulleys can fail and are available separate to the alternator.
Did you replace the belt when you replaced the tensioner?
Have you replaced the crank pulley also?
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Old 15-04-2017   #3
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Re: auxiliary belt idler

[QUOTE=jackwhoo;4258063]I can confirm that the pulley on the alternator can have a one way freewheel mechanism to reduce load on the drive belt.


The free wheel action enables the alternator rotor to turn without turning the pulley in the normal direction of rotation.


In effect the alternator can run faster than the pulley while the engine slows down.


These one directional pulleys can fail and are available separate to the alternator .

a

Did you replace the belt when you replaced the tensioner?
Have you replaced the crank pulley also
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Old 15-04-2017   #4
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Re: auxiliary belt idler

Thanks jackwhoo. Is it only the alternator that has one?
I seem to remember that the alternator is a pig to get to. Is there a guide anywhere on how to replace the pulley without removing the alternator and is there a part number?

I did replace the belt and the crankshaft pulley looked fine
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Old 15-04-2017   #5
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Re: auxiliary belt idler

I see they are on ebay! Still want to know about fitting and if there are other one way pulleys
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Old 15-04-2017   #6
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Re: auxiliary belt idler

I just wrote a long reply including part numbers but timed out and lost it all
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Old 15-04-2017   #7
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Re: auxiliary belt idler

just alternator has one way pulley.
It still could be your crank pulley , they have built in torsional vibration damper built in which fails.
Are you going to do this yourself?
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Old 15-04-2017   #8
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Re: auxiliary belt idler

find out which part has failed before spending money is my motto.


remove belt , by hand rotate alternator pulley , does it turn smoothly in both directions?
is it easier to turn clockwise or anti clockwise?
by hand spin pulley clockwise then attempt to stop pulley, can you hear or feel rotor still turning? is the pulley attempting to turn your hand?


how many miles do you drive a year?
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Old 15-04-2017   #9
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Re: auxiliary belt idler

How many miles has your alternator been in use for?


if it does turn out to be the alternator pulley a special tool is needed to hold the centre while undoing the retaining nut or bolt, factor that into cost.


If there is access to change the pulley without removing alternator there is clearly a time saving.


Mr Auto appear to have very reasonably priced alternators on ebay or you could even try their main site. worth trip to main site to find part number from VIN then try part number in ebay shop.


When you know which part needs renewal you can then make your choice.
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Old 15-04-2017   #10
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Re: auxiliary belt idler

I had exactly the same problem this week. I removed the belt and all the pulleys and idlers ran freely. Then fitted a new tensioner which made no difference so I fitted a spare secondhand dayco crankpulley I had which looked in perfect condition, but that made no difference either. As Europarts had a new crank pulley in stock on an Easter offer I bought one. Fitted today and now all is running smoothly.
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Old 15-04-2017   #11
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Re: auxiliary belt idler

Actually it was from GSF, came with new bolts and was under 60, my local Europarts were a similar price but had no stock.
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Old 15-04-2017   #12
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Re: auxiliary belt idler

The alternator pulleys do fail, and are used by several vehicle manufacturers. As these were invented by the alternator manufacturers, there are only a few sizes, but it is important to get the right diameter, right number of grooves and right offset. Good listings on Ebay show these measurements.

If the freewheel is giving up it is important to change it. As well as reducing the load on the alternator when the engine slows, it also helps dampen the engine's natural vibrations. Without this the alternators have been known to crack, so best to remove for a good inspection before buying just a pulley.
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Old 16-04-2017   #13
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Re: auxiliary belt idler

Hi
Now wondering if it is the alternator pulley. The ebay descriptions say the pulley only acts on deceleration. The effect I have is all the time.
Am wondering if it might be the crankpulley but this just seems to be a solid pulley bonded to inner piece with rubber. It doesn't appear to have failed
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Old 16-04-2017   #14
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Re: auxiliary belt idler

When I changed my tensioner it reduced the noise by quite a bit but it wasn't until I changed the belt a few weeks later that cured it completely. The old belt still looked good but had been stretched which I didn't appreciate until I put the new one on.
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Old 16-04-2017   #15
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Re: auxiliary belt idler

Quote Originally Posted by jackwhoo View Post
find out which part has failed before spending money is my motto.


remove belt , by hand rotate alternator pulley , does it turn smoothly in both directions?
is it easier to turn clockwise or anti clockwise?
by hand spin pulley clockwise then attempt to stop pulley, can you hear or feel rotor still turning? is the pulley attempting to turn your hand?


how many miles do you drive a year?
how many miles has your alternator been used for.


try the tests described , post your findings and answer the questions posted


You cannot tell if crank pulley good by visual inspection.
Forestry man wrote a very nice helpful post earlier.


Be careful of relying on ebay information.


For instance the one way pulley does operate on deceleration but be aware the belt is accelerating and decelerating many times a second.
Every time a cylinder fires the crank accelerates incredibly quickly and then decelerates . To our ears the one way pulley is operating " all the time".
This is why duel mass flywheels , crank pulley dampers and one way drive pulleys have been invented.
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Last edited by jackwhoo; 16-04-2017 at 19:34. Reason: clarity
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