From: wcr@unislc.uucp (William Rankin)
Subject: Re: DB 200 diesel motor question
Organization: Unisys Corporation SLC
Date: Wed, 9 Sep 1992 19:30:44 GMT

From article <1992Sep08.194748.16313@tyrell.tynet.sub.org>, by rodney@tyrell.tynet.sub.org (Rodney Volz):
> Hello,
> 
> I'm the owner of a twenty-year-old mercedes 200 diesel. For my taste,
> the motor produces a bit too much smoke; especially when running full
> throttle, it leaves grey clouds of what I suspect is half-burned fuel.
> 
> 1.) What makes diesel motors smoke? Apart from the motor burning a
>     fair amount of oil, which I think is normal for a 20-year old engine,
>     I suspect there are other reasons.
> 
> 2.) Which parameters are adjustable? Someone told me, nothing besides
>     the valves would be adjustable, which I cannot believe. What about
>     fuel/air-ratio, injection pump, injection nozzles? A friend told
>     me something about parts of the injection nozzles rotating when injecting
>     fuel in the chamber. Is this right?
> 
> Thank you very much,
> -Rodney
> -- 
>                      Rodney Volz - 7000 Stuttgart 1 - FRG
>  ==================> ...uunet!unido!mcshh!tyrell!rodney <===================
>   Tyrell: +49 711 651429 V32bis Public access - rodney@tyrell.tynet.sub.org
>   \_____________ May your children and mine live in peace. _______________/

Being the owner of a Diesel (albiet GM) I can speak to some of this:

The black smoke from diesel engines is the result of improper
combustion of the fuel. The first and most likely cause is a dirty
air cleaner or other obstruction in the intake path. If this 
is not the case, the second most likely cause is dirty injectors.

A dirty injector does not atomize the fuel completely leaving
larger droplets and uneven distribution of fuel in the combustion
chamber. This results in higher quantities of unburned fuel or black smoke.
A local diesel mechanic once told me to run a quart of automatic
transmission fluid thru a tank of fuel and this will clean the injectors
about as much as possible without removal. This worked great for my
engine and after 100K miles, it still doesn't smoke. (However, ATF 
DOES smoke like crazy while your are burning it.)

The only other adjustment of which I am aware that will affect smoke
is injector pump timing. On my car, this is set by rotating the injector
pump itself, much the same way the distributer is rotated on a gasoline
engine. Diesels, however are much more sensitive to timing. In my car
I can detect a difference of +- .5 degree.

To my knowledge, injectors have moving parts but are not adjustable
without removing them (if they are adjustable at all, mine are not.)

Valves may cause smoke if they are not seating completely because
of carbon buildup or if oil is leaking around the valve guides/seals.
I belive both will cause white/blue smoke.

The same mechanic mentioned above cleared most of the carbon out of
my engine by an unusual process. In neutral, he floored the accelerator
and pegged the tachometer and kept it there for about 30 seconds.
The goverener on the injector pump is set to limit at about 4500 RPM.
Even at this speed, (quite impressive for a 250CID diesel) the engine
sounded ready to explode. The results were dramatic, because a large
amount of black soot came from the exhaust and I noticed much cleaner
exhaust afterwards. I do not recommend this procedure to anybody else
but do it regularly on my own car. (Note, cranks, bearings and rods
are much more robust on diesels than ordinary gasoline engines. Except
of course, older 350 GM diesels which routinely blow the cranks out the
bottom end.)

Sorry if I rambled, and feel free to correct any errors.

Bill R.