Why do diesels 'clack'?

[jonwright]

So I've poked about and couldn't find anything on the web this AM.

After trecking up a long hill and listening to the engine under load, my inital reaction was to freak out because over the year riding 2 stroke dirtbikes that clacking noise means your top end is about to go. But just as quickly I realized the engine is just doing it's job.

Now. Why does the diesel engine clacks like it does?

I know that compression is the source of ignition for diesels vs. spark and I think I know the basics of the engine but I'm curious as to what it is that I'm really hearing.

 

[Tbar]

Alot of the noise you are hearing is the injectors working. When you have air introduction into the fuel system this noise gets louder.

The noise also increases at the end of an oil change cycle. The antifoaming properties break down and air bubbles are introduced into the high pressure side of the injectors.


Tbar

 

[spindrift]

In addition, atomized diesel fuel combusts very rapidly. A lot of the diesel "clatter" is the rapid-oxidation of fuel between the cast-iron heads and aluminum piston crowns. Shhweet sound, huh?

 

[DavidJ]

As long as you don't get the "Clacking, Bang!, Ka-put" sound.

 

[powerboatr]

Alot of the noise you are hearing is the injectors working. When you have air introduction into the fuel system this noise gets louder.

The noise also increases at the end of an oil change cycle. The antifoaming properties break down and air bubbles are introduced into the high pressure side of the injectors.


Tbar

nicely said
and the plain ol compression noise also helps to make distinct rattle
not to worry

 

[Hoss 350]

So I've poked about and couldn't find anything on the web this AM.

After trecking up a long hill and listening to the engine under load, my inital reaction was to freak out because over the year riding 2 stroke dirtbikes that clacking noise means your top end is about to go. But just as quickly I realized the engine is just doing it's job.

Now. Why does the diesel engine clacks like it does?

I know that compression is the source of ignition for diesels vs. spark and I think I know the basics of the engine but I'm curious as to what it is that I'm really hearing.

with a 7.3, you could be getting another noise known as cackle, too. THis noise is intermittent, sounds like someone is banging on the engine with a hammer. It is due to starvation of one of the injectors at the end of the "dead end" fuel rails in the 7.3 system. Particularly loud, obnoxious, intermittent clacking could be cackle.

What is more, the 7.3 is a particulary noisy diesel engine. It makes a lot of noises, and sounds different under every load condition, under every temperature condition, and sometimes, just because it feels like it.

But, the base of the matter is what the other guys said, high-pressure combustion noise and injector rattle pretty much sum up why diesels are so noisy/

 

[02SilverStroke]

Why does the diesel engine clacks like it does?

I couldn't resist this: At least a diesel "clacks" rather than "clicks"
At least they don't go "hmmmmm", although I'm sure the tree huggers wish they would.

 

[jonwright]

well, if they can make a truck that gets 25 mpg whilst pulling 10k lbs I'd be all for it.

 

[W4RLR]

They clack because they don't know the words to the song!

 

[bartman]

They clack because they don't know the words to the song!