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[Tick Tock]

Omega 2.5 V6 engine up to temperature and making a squealing noise every second.

New aux belt (2025mm) 18 months ago, but car has been SORNed for last 3 years, started regularly but long periods of inactivity. By my calculations at 500rpm tickover, 160mm diameter crank pulley, the belt should lap at 2 seconds, so now I'm not so sure what the noise could be, unless the belt squeals twice per lap?

Anyone experienced anything similar, or know what frequency any part of the engine could be attributed to 1 second frequency? (timed at 61 times per minute).

[dave the builder]

belt tensioner pulley bearing dry perhaps 
a stethoscope might help narrow it down 
I assume your timing belt and rollers are recent and not failing due to old age 

[Doctor Gollum]

Remove the aux belt completely and run the engine for absolute max of ONE minute...

And report back

[Nick W]

Remove the aux belt completely and run the engine for absolute max of ONE minute...

And report back

And spin all of the pulleys it turns.
Do that first, as it might save you some 'work'

[Tick Tock]

New cam belt and rollers fitted, as well as replacement tensioner pulley and aux belt. Removed aux belt this afternoon and ran for 15 seconds, no noise. All pulleys feel free with no noticeable slop.

So noise is obviously something to do with aux belt or pulleys, but nothing I can think of has a 1 second frequency. All the pulleys (alternator, tensioner, water pump, PAS pump and air con comp) will be spinning faster than the crank shaft, so they're out of the equation.

Perhaps it is the aux belt, but 2 squeaks per cycle seems strange?

[Nick W]

New cam belt and rollers fitted, as well as replacement tensioner pulley and aux belt. Removed aux belt this afternoon and ran for 15 seconds, no noise. All pulleys feel free with no noticeable slop.

So noise is obviously something to do with aux belt or pulleys, but nothing I can think of has a 1 second frequency. All the pulleys (alternator, tensioner, water pump, PAS pump and air con comp) will be spinning faster than the crank shaft, so they're out of the equation.

Perhaps it is the aux belt, but 2 squeaks per cycle seems strange?

Perhaps it has taken a 'set' that is only affected by pulleys of a particular diameter?
If taking the belt off makes the noise go away, then £15 on a new belt would be hard to argue against.

[Doctor Gollum]

Remove the aux belt completely and run the engine for absolute max of ONE minute...

And report back

And spin all of the pulleys it turns.
Do that first, as it might save you some 'work'

I was kinda heading that way next, but the answer has a bearing on how to approach the next steps

[johnnydog]

If a replacement auxiliary belt doesn't improve things, my money would be on the air con compressor itself. They can stick and emit all sorts of revolution associated noises after long periods of inactivity.

[Doctor Gollum]

Noone said anything about replacing the aux belt. Yet...

[johnnydog]

New cam belt and rollers fitted, as well as replacement tensioner pulley and aux belt. Removed aux belt this afternoon and ran for 15 seconds, no noise. All pulleys feel free with no noticeable slop.

So noise is obviously something to do with aux belt or pulleys, but nothing I can think of has a 1 second frequency. All the pulleys (alternator, tensioner, water pump, PAS pump and air con comp) will be spinning faster than the crank shaft, so they're out of the equation.

Perhaps it is the aux belt, but 2 squeaks per cycle seems strange?

Perhaps it has taken a 'set' that is only affected by pulleys of a particular diameter?
If taking the belt off makes the noise go away, then £15 on a new belt would be hard to argue against.

New cam belt and rollers fitted, as well as replacement tensioner pulley and aux belt. Removed aux belt this afternoon and ran for 15 seconds, no noise. All pulleys feel free with no noticeable slop.

So noise is obviously something to do with aux belt or pulleys, but nothing I can think of has a 1 second frequency. All the pulleys (alternator, tensioner, water pump, PAS pump and air con comp) will be spinning faster than the crank shaft, so they're out of the equation.

Perhaps it is the aux belt, but 2 squeaks per cycle seems strange?

  
Doesn't hurt to think about other possible causes though....

[Doctor Gollum]

Overlooking the obvious...

Was the aux belt fitted the same way round...

They can object to being fitted so that they are effectively runnong in reverse...

Typically they are marked in direction of travel.

Pop it off a run the engine. If no noise refit the original belt in the opposite direction of rotation and report back

[terry paget]

Does the squeak frequency vary with engine speed?

[Tick Tock]

Does the squeak frequency vary with engine speed?

Yes  but becomes less of an issue as the engine noise drowns out the squeak / squeal.

Just been out there and ran the engine for 20 minutes with all lights on to provide the engine with some load. There's no noise at all when it's cold, only squeals when it is nearly up to temp. So in summary it does look like the aux belt is at fault, even at twice a lap. I'll avoid going out there today to change it around (or even put the old belt on), as it's due its re-test tomorrow, and at the moment it isn't exactly broken.

Incidentally, this belt has been mentioned a while back, as I struggled to get a standard size on there (James CDX will back me up here), hence fitting the 2025mm belt, which I'm beginning to think is the problem, especially when it gets warm. 

[Tick Tock]

Think I've answered my own question - new new belt on order 

[Doctor Gollum]

It goes around the tensioner and then slips on over the waterpump pulley.

Trying to fit the standard belt any other way is a hiding to nothing as it won't fit over the flange of the other pullies.

[Enceladus]

Incidentally, this belt has been mentioned a while back, as I struggled to get a standard size on there (James CDX will back me up here), hence fitting the 2025mm belt, which I'm beginning to think is the problem, especially when it gets warm.

6PK2020 is the correct size and is the length of a Vauxhall original for a V6 with aircon.. Other makes are sometimes nominally shorter or longer. EG. Gates branded belts are slightly shorter, I seem to recall. Try to get a ContiTech (Continental AG) which is an exact 2020mm and I've never had a problem fitting one.