Engine noise

[Sajk]

Hi,

This is a big ask but can anyone suggest a cause for the rattle on falling revs in the attached clip.

Facts.
M52tu 2.8
78k kilos
Owned since new
Noise worse when oil hot. Hardly audible with cold oil
Vanos anti rattle kit in
Cat cams sport camshaft
3.0 intake manifold
Runs very well. Pulls hard to redline
Uses no oil at all
Chain tension spring replaced. The one on the side of the engine.

We even tried a brand new vanos unit. No change

The fact that's its worse when the oil thins out makes me think it's hydraulic related. It very hard to tell where it comes from. Sounds like it comes from around the vanos but you know what engine noises are like.

Edit. Having trouble attaching clip. OK got it

 

[Sajk]

Nobody?

 

[Trevor /chedder]

Could it be exhaust related? Something changing when hot?

 

[t-tony]

Sounds to me like the lower crankshaft pulley damper is breaking up. Try taking the Vee belts off and do that. If it's still there it would point to the pulley. If you listen you here the noise come in on the overrun as the engine is slowing down.

Tony.

 

[Sajk]

I also thought of exhaust but @Tony this makes sense. It is always on overrun.

 

[t-tony]

Something we used to get at work, mainly on diesel vehicles but almost always on engines with dual mass flywheels. Which would be the next point of call.

Tony.

 

[Sajk]

Is the one on the crank?

 

[t-tony]

The front pulley is on the front of the crankshaft and the flywheel (DMF) on the rear end. Best guess is front pulley.

Tony.

 

[Sajk]

Thanks. If it fails what happens? As in what goes boom.

 

[t-tony]

If the front pulley falls apart you risk the fan shroud, radiator, belts all getting mangled.

Tony.

 

[t-tony]

Check this.

Bad Crankshaft Pulley Before and After

youtube.com

Tony.

 

[Sajk]

Thanks. Will do that test on the weekend.

 

[Sajk]

Non of the pulleys seem to have any movement at all. Also noise seems worse when up to temp. Could it be oil or water pump?

 

[Dino D]

Non of the pulleys seem to have any movement at all. Also noise seems worse when up to temp. Could it be oil or water pump?

When my 2nd or 3rd water pump, can’t remember how many now(!) was going I was convinced the engine had bearing knock!

Cheap and probably due at your mileage/age.
The replacement pumps I’ve had since the original seem to only last around 15-20k before failing again, even with the metal impeller.

 

[Sajk]

Could it be disa?

 

[t-tony]

Definitely not, it is too "heavy" a knock to be the Disa. I've never heard that type of knock from a water pump let alone an oil pump.

Tony.

 

[Sajk]

And Dino's comment ? The mystery continues..... went for a long drive this arvo. Spins like a top. Pulls like train. But that noise on overrun is most disconcerting when it's warm. Not that I can hear it with the roof down in the open. Only in the garage.

 

[t-tony]

I can only offer my thoughts with almost 50 years in the motor trade and remotely at that just as Dino is offering. If you don't have any real experience I can only suggest taking it to a recommended repairer and get a " realtime hands-on" appraisal Sajk.

Tony.

 

[Sajk]

And it is appreciated Tony. My guy cannot find it. I have some experience having rebuilt one engine but not a lot. And not one of these. A twin cam fiat 1600.

I will send it back to my guy who is very experienced. We have had the valve train in bits looking for noise. What really concerns me is that it is almost not there when the oil is thick and much louder when the oil thins out like it is pressure related. Compression and leak down is fine.

It might just be that it does not like the cams and the valve train just rattles on the overrun.

 

[t-tony]

Sorry I can't be any more help.

Tony.