Crank Shaft Wobble?

nick4tl

Member
Hi everyone.
It never ends. Car went in for NCT (MOT equivalent) last week but couldn't be tested as the tester luckily spotted the auxiliary belt was badly worn. Got a new belt fitted and mechanic told me the alternator pulley was wrecked, which he reckoned could have been the cause of the auxiliary belt suddenly wearing. Got the alternator reconditioned and new pulley installed and new auxiliary belt fitted. All put together and the engine was sounding nice.
After being driven 50 miles though I started it last night to hear a very rough sound. Back up to mechanic. Sound was particularly pronounced when switching off engine. Seems now the timing belt is worn but more worryingly he sees a wobble in the crankshaft pulley that he hasn't seen before.
Going to get the timing belt, waterpump etc done. It was due in 10000 miles anyway. But has anyone had their crankshaft pulley develop a wobble? Hopefully it's not too expensive a part to replace. Wondering if anything else should be done whilst we are at it.
 
Never really thought about the a2 having one but does the a2 have a harmonic damped main pulley ? could it have failed ?
 
The rough sound was the auxiliary belt tensioner it seems. Mechanic is a little perplexed as it had seemed totally fine when he fitted the new auxiliary belt last week. Hence wondering if the wobble lead to the tensioner failing.
 
Never really thought about the a2 having one but does the a2 have a harmonic damped main pulley ? could it have failed ?
Yes I’m sure the crankshaft pulley has a rubber damper built into it, it’s worth checking the auxiliary belt pulleys for small bits of old belt as the can lodge in the small vee’s
causing irregular belt movement!
Hth
Keith
 
Had a better look today. The wobble actually may just be the whole engine being a bit wobbly on tick over. The auxiliary tensioner is getting replaced now. There is some wear on the timing belt too though so we’re going to just do all that and the water pump at the same time. And then hopefully that will be all for a while!
 
Couldn't be something daft like engine mounts needing to be renewed so that there is normal vibration but the whole thing isn't being damped normally?
 
I think that may be the case. We’re hoping it’s just bad luck the auxiliary tensioner packed it in and that what we though was a wobble crankshaft auxiliary pulley is actually just the whole engine being vibrating a bit, possibly due to worn engine mounts.
On the plus side we’ve spotted now that the timing belt wasn’t great anyway so good to get that done. The problem with this car is that it sat in my yard for about a year without being driven so it’s being a bit grumpy about being woken up!
 
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Basic test for engine mounts is to 'feel' the vibration level on the engine side of the mount then compare it with the chassis side. If the mount is doing its job the chassis side should feel significantly smoother. Just be careful and keep your fingers away from hot or rotating parts even if using a metal rod or screwdriver as a probe.

Cheers Spike
 
When engines are left standing in the open, its not unknown for a poly vee belt to stick to pulleys. When you start the ribs rip off the belt, stuck to the pulleys, as described above. This will cause excessive belt movement. Make sure all pulley grooves are spotless.
If you have excessive engine movement fore and aft, then check the dogbone mount underneath. If a new unit is required fir one for a Polo, they are cheaper!
The 3 cylinder diesels have a bonded 2 piece pulley to damp torsional vibration. An out of balance outer section is bonded to a centre hub. This imbalance is offset by an out of balance flywheel. 3 cylinder diesels tend to "nod", so the imbalance tends to move this vibration into sideways movement, which is more easily managed by the front and rear engine mounts, and the lower dogbone mount.

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thanks for the tips re dogbone. Will have a look. Currently waiting to get all the parts for an oil chain replacement together. Decided to get this done now whilst doing the cambelt etc.
 
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