black smoke

elrond8177 · Jun 21, 2003

Ok, In my younger days I was a fair mechanic. I've
even done a ring and valve job on my 289 Mustang! I
can understand how the shutoff switch could make a
difference in starting but I can't relate it to the
black smoke problem. This should either involve the
air to fuel mixture ratio or a problem with burning
oil. I'm not doubting your success and I appreciate
your input but my MD6B starts right up every time and
really doesn't have the problem until it's been
running a while. The shutoff seems to be working fine
since it stops the engine properly and it starts ok on
my way back into harbor.
If I'm missing something obvious here feel free to
educate me. At my age I've probably forgotten most of
what I ever knew about engines!! LOL
Any one else got any ideas!
Thanks again for your input
John Devany
Southern Comfort Too
V2931

P.S. Have recently met with Paul from Houston, TX on
the Overture V2929 (or a very close number to that)
and I just received my copy of 'Fair Winds'
(Newsletter of the American Vega Assn) and read an
article from Willem also from Houston Tx on V2930.
This could have been a sales related phenomenom but I
prefer to think it was the will of mother ocean and
her currents. Hope to get a few of these folks
together sometime for a 'Gulf' rendezvous!

stevebirch2002 · Jun 21, 2003

Hi

The black smoke seems to appear on most MD6 and MD7 engines when at full throttle. This is usally a sign of age and wera and tear (same as me!). Havent got any magic cures or answers I am afraid.

Kind Regards

Steve Birch Vega "Southern Comfort" V1703

maciacarter · Jun 22, 2003

Check and see if the vent from your fuel tank is clogged, or blocked. As is runs, it builds a vacuum if it isn't properly vented, and that would gradually starve your engine only after it had run awhile. If it was completely blocked it would, of course, eventually stall.

Regards,

Christine,
Oreneta, V2175

colinpspiers · Jun 22, 2003

As a retired Chief Engineer having served on many a diesel powered vessel I'd
like to put my oar into this subject.
Black smoke is almost invariably produced from a diesel when it's overloaded.
That is the demand for power is more than the engine can comfortably produce
and fuel is being injected but cannot be burnt properly hence the sooty black
smoke.
Now, either the load is unusually high (pitch too high, fouled prop,
tightness in the gearbox or prop mechanism) or the engine is out of tune ( fouled
injectors- common, bad timing- uncommon, engine worn?).
The combi mechanism on my Vega was tending to put too much pitch on before
the engine revs built up. The cure was to build up the engine speed cam with a
little epoxy metal compound to ensure the revs build before too much pitch was
applied. A simple job that worked for me.
Incidentaly black smoke

tjelle1946 · Jun 22, 2003

Hi --I agree with the smoke--I operate two diesels at 800kw each and one smokes white all the time--problem from new. Diesels smoke black when over loaded ie my pu in too high a gear for the load=black smoke. jorgen

ve7vmt2001 · Jun 22, 2003

Quite right on the exhaust smoke colours.

Black smoke

orchardprojects · Jun 22, 2003

Wow guys all great stuff to work on. Thanks.

The only problem now is that like a hypocondriac I think I have all
the symtoms! My fuel cut off valve is a bit stiff and having worked
on the prop in the winter things might also be a bit tight causing
overload. I'm tending towards the injectors judging from the colour
of the transom at the moment but then again the smoke does look very
white when running..... which brings me back to my original thought
that she is a 30 year old lady who should be allowed a few bad
habits, after all she is not complaining that I took over twelve
hours to struggle 50 miles round the Isle of Wight on Saturday!
Thanks again everyone.

David
Annabel v1745

vega1860 · Jun 23, 2003

I'm no diesel tech but I just finished a complete overhaul of an MD6A with
helpful hints from a mechanic and I do not have the problem. One of the
hints was to adjust the injection pump at 12,5 degrees (before TDC?) instead
of 10 degrees - to prevent smoke. There should be a 10 degrees mark on the
flywheel and 12,5 degrees is about 5mm to the right. This should be aligned
to a mark on the block. I think that part the reason for the adjustment was
that my bore has been honed from 70mm to 70,5mm, but perhaps you should try
playing with this timing. Can't hurt, pretty easy to do.

stevebirch2002 · Jun 23, 2003

Hi David

Well done in coming second in the Vega Class in the Round the Island Race (Out
of two entries!)

If the engine aint broke then dont fix it. It will last until it breaks. Well
done again.

Steve Birch

At 23:17 22/06/03 +0000, you wrote:

ronbodkin · Jun 23, 2003

What a great thread. Thanks everyone for some great input now I have
many things to check.

I've suspicious of the "too high of load prior to high enough engine
revs theory.

Thats one thing that frustrates me about the combi mechanism. It
has always seemed to be reving too low, and there is no way to
increase the RPM of the engine relative to the prop speed.

I had so much black gunk on my transom this weekend I couldn't even
scrub it all off!

Strange thing is, the engine starts very easily and performs well.
On one hand I love Steves "if it isn't broke don't fix it" theory
but it is making me neurotic thinking that I may be doing damage to
the engine when there is some relatively easy fix out there
somewhere.

A local "Clif Claven" type (expert at all things) at the marina
warned me not to run the engine smoking black because the soot will
eventually clog the exhaust and cause back pressure and ruin the
engine.

Any thoughts on that from the actual Diesel Mechanics on the list?

pfmarrack · Jun 23, 2003

I think John has a excellent idea for a Gulf Rendezvous. Sounds like
fun. I will need a little time to get "Overture" a little more
seaworthy, but I'm game. Any other's?

Paul
V2926

frank_lighthouse · Jun 26, 2003

Can I indicate a simple and cheap way of curing this problem (which was also evident on 'Alkira').

I would suggest that the engine speed cam profile on the Combi is not ideal, particularly for an old engine and certainly in my case there was not a clearly defined engine idle point - so make one!
This item on Alkira now sports a narrow 1.5 mm thick 'lump' (for want of a better description) of brass soldered to the cam itself in the neutral position and with the profile blended into the original cam profile.
The engine idle speed is set with the roller on this 'lump'. Once the 'prop control lever is advanced however the roller descends from this peak and provides more rpm than was the norm at that particular 'prop pitch previously.

Seems to work for me.

Best regards,
Frank Fowler, 'Alkira', Liverpool.