Smoke and Cycling MD6A Speed

jimmyvusa · Aug 26, 2003

Ed:

I am very sorry to hear of your recurring problems with the Volvo/Combi. I wish I knew enough to come across the Sound and help you out. I am a mechanical "5 thumb" type. Sometimes you more knowledgeable mechanical types out here give me an inferiority complex. I have one suggestion. Once, last year, the the conduit pipe carrying the Combi control cable loosened on our boat. The cable stretched and did not properly engage/control the system. I was very concerned and hitched a ride back into port. A good friend who is a genius, opened the cockpit sole looked things over and hand tightened the control cable conduit/pipe. Immediately the Combi drive was fully restored. We loosened the conduit again, greased the cable, and so far so good. If not you perhaps this experience may help others.

Here's hoping you can get some good advice out here. There is definitely some Vega Voodoo working in your case.

Kind regards...........Jim

SaylerEd@... wrote:
Hello All:

Saylered here again (still?). I continue having problems with my MD6A with
combi drive, and have exhausted all I know and think of. Also, very difficult
to find anybody qualified to come and work on it.

Problems are as follows: Engine starts easily on first revolution and idles
nicely with no smoke. Whether allowed to warm up or not, engine will speed up
properly when power is applied, but after about 20- or 30 seconds, it will
slow to about idle speed while putting out gray exhaust smoke, stay at this speed
for five- or ten seconds, then resume speed while putting out darker smoke on
accelerating. Then it will continue this cycle with about a 30 second period.

Now, here's what I have done: I had new nozzles installed in both injectors
and, of course, snap tested. After reinstalling the injectors, the engine
seemed to run pretty well for two- or three minutes, then reverted to its old
problem. I have removed the fuel line from the output of the electric fuel pump
(which is also the suction of the attached pump) and run a hose from a clean
diesel fuel source on the cockpit seat, directly to the attached mechanical fuel
pump, thus bypassing everything from - and including - the fuel tank up
through the pre-filter and the electric fuel pump.

The problem continues........Have any of you ever had a similar problem and
corrected it? If so, please be so kind as to share your experience with me
(us). The sailing season is almost over here in Connecticut and we have been out
only three times.

I thank you in advance for whatever information anybody may have.

Ed Davis.........aka......saylered@...Yahoo! Groups SponsorADVERTISEMENT

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bv0820 · Aug 26, 2003

Don't give up...I almost did. I had a degenerting
problem over the course of a season and at one point
it didn't run. My problems where traced to the
camshaft gear wheel, itermediate gear and injector
gear...it is a gear timing issue. The original MD6A's
where mfg with a "plastic washer" on the gears. At
some point it was changed to a steel-rubber one. When
I opened the area up the gears where missing
teeth..therefore the timing was off. Hand to replace
all three gears..reset the fuel injector pump (if you
haven't checked it recommend) If you have the manuals
an engine guy should be able to set it up...Since I've
relocated to Fl lost my contacts...where in CT are
you..PS if the above is your problem I have one of the
gears and know of a great source for MD6A used parts.
Give a call if I can help 772-215-8087

Bob Vogel
Laughing Gull
1877

chris20636 · Aug 26, 2003

Thanks, Jim:

I have already crossed that particular bridge, tightening and lubricating
the control cable.

I have put in many hours and several hundred dollars trying to find the
cause of this cycling problem.

If anybody has had any problem anything like this, please share it with me.

Thanks...................Ed

elrond8177 · Aug 26, 2003

Just a quick two cents here: #1 When I read your
symptoms I also got the impression of timing problems.
Although this may sound strange your comment about it
starting so well 'on the first revolution' made me
think back to an old 289 Ford engine that I rebuilt
years ago. I know it's not a diesel but the principle
is the same. At the time I couldn't get it started
until I rotated the timing 'too far' advanced. Then it
would start right away but then it wouldn't run right
at higher RPMs. Since it involved both compression
timing and spark timing the problem was more
complicated but proper alignment finally did solve
that problem.
#2 I'm not sure whether you said you completely
bypassed ALL the fuel filters but earlier in the
season I also had a problem with black smoke. After
replacing the fine fuel filter and completely cleaning
the water separator/filter that problem went away.
I've since added that task to the spring cleaning
list.
Good luck!

John Devany
Southern Comfort Too
V2931

colinpspiers · Aug 26, 2003

Hi Ed,

Your comment about exhausted reminded me of when serving on an old steam ship. When we were going to shut down the main boiler we hand started an old Lister diesel generator. Now the exhaust system had a valve up in the funnel area to stop rain etc entering the mostly idle engine. If we forgot to open that valve the engine would start, run perfectly for about 5 minutes then exhaust back pressure would cause her to start fading sometimes stopping but often spluttering on at low revs.
I'm suggesting you have a look at your exhaust system for collapse or partial blockage.

Regards Colin "NAIM" V1400

tjelle1946 · Aug 26, 2003

over time soot will build up--try rodding out with wire brush--2 cycle engines will soot up until they no run. jorgen

stevebirch2002 · Aug 26, 2003

Hi Ed

Only thing I can suggest is the Injector Pump?

Regards

Steve Birch

At 13:11 26/08/03 -0400, you wrote:

stevebirch2002 · Aug 26, 2003

Hi Ed

Another cause may be very simple. Just had it happen to A Vega in Weymouth and
it happened to my first one. Take the Rocker Cover off and see if that
cures it
as the decpmpression lever may be snapped inside. This is quite common as the
gasket needs to be quite thick and the supplied replacement ones are very
thin.
Sounds impossible but this was the problem cure for at least two Vegas in the
UK.

Regards

Steve Birch

At 13:11 26/08/03 -0400, you wrote:

nhrjw · Aug 28, 2003

Ed,

Had a somewhat similar problem, but of course different. Engine ran
fine till max speed. Then it would just die. Throttle her back and
she would start to run fine. Attempt to go for max speed, and she
would stall. If I could throttle back fast enough, the engine would
keep running, if I could not, then it would die, but would start up
without problem providing I throttled back. Rebuilt the injectors
and the pump, and it went away.

What concerns me is the following - you have grey and then black
smoke. Black smoke with a diesel is either too much fuel, or not
enough air. If I remember correctly, there are mechanical weights,
like in a distributor in a car, that regulate the speed of a diesel
which are in the injection pump. I'd look towards the pump.

My problem did not produce any smoke. But the surging makes me think
it is a fuel delivery problem. I did not have any problems with the
engine before this happened and have not had a problem since. The
rebuild on the Injection pump and injectors was about $575. If you
mark the pump location and don't rotate the engine, it should bolt
right back in without having to retime it.

Jeff Noland

chris20636 · Aug 29, 2003

Jeff, and Others:

Thanks for the advice and suggestions on the problem I've been having with
my MD6A.

I spent the day on VESPER (V 1868) with a very knowledgeable (and expensive)
diesel mechanic. He, after considerable troubleshooting, thinks that the
problem is, indeed, in the high-pressure injector pump, as Jeff Noland suggested.
We removed it and I took it to a shop in Deep River, CT that specializes in
diesel engines. I should get it back next Thursday. I'll post the end results
after some serious sea-trials.

Also removed the exhaust manifold to get to the pump. I'll rod out and clean
the manifold while it is available. I had already taken the injectors to the
same shop for overhaul.

Again, thanks to all who took interest and offered advice and suggestions.

Ed Davis