Why do diesels clatter at low revs?

[StuH]

My 535D is my first diesel, at startup and particularly when cold it clatters a lot. Is this the case with all dervs or have i got a problem?

Is there nothing that can be done to reduce this and make them sound a bit better?

Apologies in advance for dumb question

[Johnbmw6]

I have just bought the 635D Sport, and on start-up it sound diesely, once warm after say 5/8 mins it's quiet, thats the latest diesels, the older one's clatter a lot longer.

[grumbledoak]

Ok, curiosity strikes. Anyone technical know what exactly is clattering?

ETA- Two stroke motorbikes can sound like a tin can full of nails. Is it similar?

Edited by grumbledoak on Wednesday 12th March 20:23

[dxb335d]

grumbledoak said:

Ok, curiosity strikes. Anyone technical know what exactly is clattering?

Not sure on the diesel, can only presume its ''diesel knock'' but on a petrol more likely to be cam followers etc.

[Slinky]

grumbledoak said:

Ok, curiosity strikes. Anyone technical know what exactly is clattering?

AFAIUT, it's the injector pump... although I could be talking bobbins...

[grumbledoak]

dxb335d said:

on a petrol more likely to be cam followers etc.

Makes sense. The Speed 6 sounds like a sewing machine 'til she warms up!

[cptsideways]

grumbledoak said:

Ok, curiosity strikes. Anyone technical know what exactly is clattering?

ETA- Two stroke motorbikes can sound like a tin can full of nails. Is it similar?

Edited by grumbledoak on Wednesday 12th March 20:23

Its actually diesel knock & normal (its how a diesel works) modern Tdi/CDi engines will do this until warmed, its a bit like a choke system, it chucks in more fuel at different more advanced timing to normal to warm the engine & cats up quickly. Once warm it'll revert to standard settings & new diesels inject multiple squirts of fuel per cycle to lessen the knocking noise