Hi
Looking for any help/info on why the pulley tensioner wheel, on the auxiliary drivebelt, of my 2004 1.9d polo keeps shearing off. Does anyone know if it is possible to bypass this tension wheel until I can get it to the garage?
absolutely desperate and at my wits end with it!!
{typo in header corrected}
Edited by Dynamic Dave on 22/06/2009 at 11:15
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Probably because the one way clutch inside the alternator pulley has seized. These are readily available as pattern spares and usually fail at about 80k miles. You need 2 splined tools to change it.
Running with a seized pulley wreaks havoc in the drive due to the engine torsionals being magnified by the (high) drive ratio. As the alternator rotor has the highest speed and highest inertia, it needs to be decoupled from the source of perturbation otherwise damaging oscillation will occur at certain engine speeds.
That's why the tensioner bolt is breaking. Fix the real problem quickly.
659.
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Thanks for the quick reply 659.
I had the alternator replaced during the week but it's still happening. Do you think that something else could be causing the clutch to seize? or could I be so unlucky as to have another faulty alternator!!!!
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Was the pulley replaced with the alternator? Usually, alternators don't come with a new pulley, and it gets swapped from the old one.
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The pulley was replaced first because the first time it came off it actually shattered the pulley wheel. The new alternator was then fitted but it has broke 4 times since but these times only shearing at the bolt.
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Sorry, I'm talking about the pulley that's on the end of the alternator - the one described by 659fbe - you don't generally get a new one with a new alternator.
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ok sorry I get it. It is the tension pulley that keeps coming off but do you think I also need to replace the alternator pulley?
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Also check that everything is in line,I had a car that sheared crankshaft pulleys,it turned out that the dynamo(yes,it was a while ago) was slightly out of line and was imposing a sideways force on the pulley.
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>>do you think I also need to replace the alternator pulley?
Possibly - it is definitely worth checking.
The alternator pulley incorporates a freewheel mechanism.
As the rotary motion of the crankshaft isn't smooth, (every time a cylinder fires, the crankshaft suddenly accelerates), the belt is also always changing its speed faster and slower, many times per second.
As the alternator has both a heavy rotor, and a small pulley, it's the most difficult component to drive with the rapidly changing speed of the belt. Add to that the fact that the belt is not absolutely rigid and you get the possibility for the alterator to begin to vibrate at resonance, rotating faster and slower than the belt. This vibration could over-stress the belt and everything else connected to the belt - like your breaking bolt, for example.
The freewheel allows the alternator to over-run, and prevents these damaging vobrations from building. If the freewheel fails, the pulley tends to lock up solid.
So, check the pulley, and make sure that it freewheels properly. If you fing that it doesn't freewheel, then, it's worth renewing.
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Elegantly put by my Learned Friend.
You can actually check the operation of the frewheel pulley in situ if you are careful.
If you look inside the alternator (engine stopped) at the pulley end you will see the copper coloured stator windings. Inside the stator and projecting slightly from the rotor is the alternator internal fan. Take a small screwdriver and attempt to revolve the rotor fan blades clockwise as you look at it. It should turn without appreciable effort. Attempts to turn anticlockwise should meet with solid resistance - don't bend the fan blades.
Be careful not to damage the enamel on the stator windings when you do this test.
659.
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Thanks for all your help and info folks. I hope I'm not tempting fate by saying that's it fixed!! Belt was out of line because the wrong alternator had been fitted. Strangely now I feel that the steering is heavy at times but VW says maybe I'm just paranoid!!!!!
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I've got exactly the same problem on the same car. The bolt initially snapped and a new tensioner/bolt was fitted along with a new belt (which was not a genuine part). The second tensioner snapped across the casting (not at the bolt), and both the tensioner and bolt were replaced. The third tensioner snapped off at the bolt again, so I took the car to a different garage.
The new mechanic managed to refit the third tensioner by replacing the bolt only. I've had the aircon compressor replaced as my he felt that seizing was likely to be the cause. The aircon is a lot colder now since the compressor refit necessitated a re-gas, but that's beside the point -- the tensioner snapped again this afternoon. Obviously the latest tensioner was either weakened when the bolt snapped off before, or as suggested above the alternator pulley is seizing. Or both, I suppose!
I've asked the mechanic to replace the alternator pulley as well as the tensioner and the drive belt just in case the first garage managed to a fit a belt that's too small.
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I've found the discussion topic as I too have experienced the same problem. The alternator was replaced - it came with a new clutch pulley but has since sheered 2 more bolts. The most recent bolt was a genuine VW part (number N0195433) and that lasted a week. The aircon compressor hasn't been changed and the pulley operates smoothly enough. Can anyone recommend other checks/fixes please?
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I suggest you have the crank damper pulley checked for movement/play. Regards Peter
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