Strange noise in engine (M54B25)

[Shooter]

Hi there.

For some time now, there has been a strange (and a bit frightening...) noise coming from the engine. It seems that it is getting a bit louder with the passing time.
The sound can be heard at idle, when the engine is warm. It follows the engine revs. It sounds a bit like a belt rubbing against a pulley, which was my first thought, the alternator/water pump belt/idle pulley and so on. But it also has some kind of a metallic sound to it.
I've looked at a number of videos on youtube concerning the idle pulley, but it seems that this is not my problem. The sound does not come from the front or left side of the engine, but rather from right down the middle of the cylinder row. And the metallic part of the noise does not sound like a rubber belt would.
It sounds a bit like the sound of the N52 faulty hydraulic valve actuator, but not as dramatic.
I've looked for :
- DISA : noise seems to be located around the DISA, but towards the middle of the engine; i've tried to unplugged the DISA power supply while the engine is running, it made no difference;
- VANOS : the sound clearly does not come from the VANOS unit, and it is not as loud as the videos i've found on youtube;
- idle pulley/alternator belt : not sure;
- chain tensioner actuator ?
The car has 106.000 km now, was produced on 10/2003 and is equipped with the M54B25 engine. I take very good care of my car, especially the engine. Oil changes are made by myself, always using premium grade oil (low SAPS, BMW LL01 approved 5W30 oil, from Elf, Total or Castrol), on a more than required basis (something along every 15.000 km), changing the filter at the same time. Car has been serviced at a BMW dealer for Inspection II at 90.000 km.
The car runs smoothly, there is no "hickups" or anything. Acceleration from idle to redline is smooth, there is no hesitation or missfire (that i can feel at least). As far as i know, the engine has never been "over-reved". That's also why i don't think it's the VANOS unit.

Right now, i'm thinking about a hydraulic actuator, or a valve spring, because of the location of the sound and it nature. Is there a way of telling without taking the engine apart ?

Next week-end, i will try to remove the DISA unit to inspect it visually, along with the throttle body and clean all this.

If you have any clue, i'd be glad to hear them.

 

[tibi_t]

http://www.youtube.com/watch?v=MulqcY3PIdQ
Is this the sound you are talking about? I have it on mine but I have not found the source of it.

 

[Shooter]

Hi.
I doesn't seem to sound exactly like it, but i cannot be sure.
I have really (well, i had...) two distinct noises : one is definitely coming from the alternator belt pulleys, the other one was a metallic sound coming from (i'm quite sure of it) a hydraulic actuator.
This actuator noise is now gone. At first (i was petrified...), it was rather discreet, then become more and more loud, and then it was gone. I'm thinking that something went wrong with one of the hydraulic actuator, it was stuck or badly lubricated, but now, either it's completely broken (but i don't think so) or it has come back to normal operation. Again, the engine runs smoothly.
For the pulley noise, i tried to spray all the pulleys with some WD40, the noise is a bit less... well, noisy, but still there.

Anyway, my car now enters a period of major overhaul. Yesterday program was :
- oil change with Castrol Edge 5W30; it costed me more in oil than the regular oil service by BMW :x
- air filter cleaning;
- idle valve cleaning (thanks to the DIY i found here and on zpost);
- DISA inspection (was clean and does not have any play);
- alternator belt pulleys sprayed with WD40;
- fitting of the RPI intake scoop at last.

I cannot say for sure that the engine runs smoother at idle, or if it does pull a bit stronger at 100+km/h, but i'm rather glad of my yesterday's overhaul program.

Next step will be to take care of the silent-blocks, both the front lower control arm ones and the rear diff ones. Then the alternator belt pulleys. Then the bumpers, front and rear (ha... Paris... ses voitures et ses abrutis qui se garent n'importe comment...), then complete detailing.
If everything goes right, i'll have a nice running and looking car for the Islay meet.

 

[ronk]

When you find out let me know PLEASE !!!!

I went thro all the hoops a long time ago. The car went into the dealer under warranty and they replaced the belts, checked the idler / tension pulleys, water pump etc and all were fine. The replaced the Crank Damper as the rubber was starting to extrude but to no avail. It s silent when cold, like a sewing machine but it rattles when warmed thro. If the car is on an incline (cant remember which way ie nose up or down) the noise is subdued and qute acceptable.

The end result was the BMW Main dealer Guru said don't worry! I dont, I just ignore it and pay for a warranty each year!

If you do a search on here, you will find quite a few complaints. One member had an oil pump replaced and that cured it he said.