Squealing drive belt, keep reading though!

[jmattley]

Hi all,

 

On my CR170 VRS, I recently changed the turbo which involved the car not being driven for 3 weeks. 
 

Straight away on the first drive it developed a squeal. So, changed the drive belt, now it squeaks more!

 

The alternator, AC pump and tensioner all spin freely and I also cleaned them with degreaser. The tensioner spring feels firm, so I would’ve thought it’s fine, but maybe it has to be super strong to not squeal?
 

Any ideas why it could still be squealing?

 

BTW, it’s an 09 plate so getting on a bit. 
 

cheers!

[MikeTheThinker]

Does it squeal at engine speed or road speed?  Also, does it squeal if coasting with the engine off?

[jmattley]

Just at driving speed. It’ll squeal when revved at stationary at around 2k rpm. When driving it only squeals when the engine speed increases. It doesn’t squeak under load unless it’s accelerating (correct gear selection etc). It’ll squeal if I coast and rev it (3k rev limiter at idle when the handbrake is on). 

[Guest]

Does the squeal disappear if you douse the belt in water?

[jmattley]

No difference. 

[J.R.]

Alternator pulley one way (sprag) clutch failure if you look you will see the tensioner and the slack side of the belt oscillating.

Edited 1 October, 2023 by J.R.

[Guest]

I'd run it with the belt off, could be the turbo.

[jmattley]

@J.R.Thanks! So how would a failed sprag clutch make the belt squeal? Would it be stuck permanently coupled or slipping occasionally?

Edited 1 October, 2023 by jmattley

[jmattley]

5 minutes ago, MicMac said:

I'd run it with the belt off, could be the turbo.

I really should have done this the last 2 times I lifted it and took the belt off! I should probably check though. Hopefully it’s not the turbo making a squeal as I’ve just changed it and it’s pretty young (60k miles). 

[J.R.]

It slips then locks and the inertia of the alternator causes the belt slack, tensioner movement and belt squeal.

 

Better than my description would be to try moving it in both directions by hand, you will feel exactly what is going on inside and it isn't pretty!

 

Instead of the rollers climbing smoothly up & down the ramp the bits of broken rollers floating around cause them to snag.

[jmattley]

1 minute ago, J.R. said:

It slips then locks and the inertia of the alternator causes the belt slack, tensioner movement and belt squeal.

 

Better than my description would be to try moving it in both directions by hand, you will feel exactly what is going on inside and it isn't pretty!

 

Instead of the rollers climbing smoothly up & down the ramp the bits of broken rollers floating around cause them to snag.

This makes sense as it only squeals when the engine speed quickly increases. Gentle acceleration won’t do it. And it’s the same squeal sound I’ve experienced in the past with old belts, but they did it on startup like standard worn belts do. 

[jmattley]

So, update. Ran it without the drive belt. Still squeals. I guess it’s a boost leak! It honestly sounds exactly like a squealing belt. 
 

any ideas where to start? 

[jmattley]

From a quick google, sounds like it could be the egr cooler to egr valve pipe. I actually didn’t replace this gasket, so could be plausible. 

[Guest]

Have an assistant rev the engine to the squeal whilst you use a 1m length of garden hose to pinpoint the sound, hold one end to an ear and probe with the other.

 

I would suggest a boost leak is more a hissing/whistling sound.  Your squeal and recent turbo replacement may indicate a faulty turbo or it's oil system.

Edited 1 October, 2023 by MicMac

[jmattley]

Update!

 

So, I replaced the EGR cool pipe to EGR  valve gasket, but before I did ran the engine with the bolts loosened slightly so there was a small gap around the gasket then also with the pipe fully disconnected from the valve. 
 

With a tiny gap, it still squeals. Slightly larger at around 2mm, the squealing stops, then fully disconnected it sounds like a tank but also no squealing. Changing the gasket did not stop the squeal. 
 

Since the squeal stops with the a slight gap, I’m feeling that it releases enough pressure in the pipe to stop a hole or gap elsewhere from passing gas at high enough speed to squeal. 
 

I think my next step should be to check gaskets at the other end of the pipe (but they’re are new annoyingly) and also maybe the pipe for splits. 
 

@MicMac, I’ll also use your hosepipe stethoscope idea to help narrow things down too.