E90 320i Engine Knock at Idle

[sirgomer]

https://www.youtube.com/watch?v=ZcJPwgXfCP0

Hi all. I have an engine knock at idle on my 2008 BMW 320i E92 Coupe.

It first happened a few weeks ago but went away that evening as well. Haven't heard it since but its done it twice now recently, when the engine is hot and only at idle. If you rev it goes away. It seems to be coming from (see video link) whatever the item is next to the engine block, just to the right there (I am no mechanic!).

Car drives fine, no loss of power, no difference in economy, oil OK and on proper fully synthetic oil (Castrol) as recommended, had all new injectors etc only a few months ago and was fine until this. No difference in drive or performance as I say but a horrid knocking sound at idle when it feels like doing it. Don't know if its the item to the RH side of the engine block or the alternator below.

Any ideas at all guys? Thanks in advance. I don't see what it can really be with no difference in performance or anything else and only does it at idle...no difference in noise or knocking at all at revs...it goes away?? :S

[ZX10R NIN]

Are you sure it's not the air con pump this would give a similar sound to bottom end knock, the easy way to find out is to remove the belt & see if the noise has gone.

[sirgomer]

ZX10R NIN said:

Are you sure it's not the air con pump this would give a similar sound to bottom end knock, the easy way to find out is to remove the belt & see if the noise has gone.

Hi mate - thanks for that. Where abouts is the air con pump and would that run without the aircon being switched on?

[ZX10R NIN]

The pump runs on the same belt as the alternator so by removing that belt you can start the car which will tell you if it's internal or not.

[helix402]

Timing chains are known for going on these.

[sirgomer]

helix402 said:

Timing chains are known for going on these.

You put your ear to the engine block though and you hear nothing but the norm, its coming from what is next door :S

[Fun Bus]

Have you checked the tension of the timing chain? You can access it when you remove the oil filler cap.

[iSore]

Timing chains don't knock though, more of a rattle. Any N43 with over 50k needs a new chain and guides* - catch it early and you can do it with the sump on as long as the guides are in one piece. Regarding the knock, remove the aux belt and try it again. AC pumps are amazing fun to change btw.

• it's not if, but 'when'. Seriously - it's £600 went spent. When the guides break up, it's curtains.

Edited by iSore on Tuesday 25th October 09:51

[Fun Bus]

No, timing chains don't knock but I wasn't sure if the chain was slapping due to broken guides and tensioner.

Having said that, I could have been listening to completely the wrong sound!

[iSore]

My bad Mr Bus - I should have listened to the video..................


That is the chain about to leave the building.

Do not start that engine again until it's been repaired.

[sirgomer]

Surely if it was the chain though it would do it constantly? Took that video that other night and the car hasn't done it since. As I say it doesn't do it cold, it doesn't do it very often, it just does it now and again, hence me filming it at night while I had the chance. Surely if its the chain and its about to go it will never stop doing it until it goes?

[sirgomer]

Just for your interest lads...

Car back and repaired. Alternator bearings had gone. On load horrid, off load fine. New alternator - job done.

[helix402]

Good job.

[iSore]

Go and buy a lottery ticket tonight!

[ZX10R NIN]

I did say remove the belt, well done OP