MD6A Decompression Problem

[bonnerwhitman]

Hi! I am new to the forum, but have had our Vega for a couple years now. I'm hoping this won't be a big deal, but realistically, it will probably require hours or maintenance and thousands of dollars to fix. We normally start our little Vega by lifting the decompression lever a little bit, allowing the flywheels to build rpms, then drop the lever and voila, she turns over. Recently a friend lifted the decompression lever as high up as it would go in an effort to start the motor. Now it seems like any lifting of the lever only results in minimal decompression.I am not a diesel engine specialist, but I think there might be something wrong with the exhaust valves? Does anyone have any helpful advice about how to correct the problem? Would love to try a list of potential fixes from easiest to most difficult . Also, any manuals or diagrams would be extremely helpful. Thanks in advance!BW

 

[dougpol1]

IT's Been my understanding that the
decompression lever should only be used when hand cranking. This
is true of most diesel engines so I have not tried it on my
Volvo. IF your starter won't start the engine with decompression
I would say your batteries are low or there is something wrong
with the starter. Possible a bad ground could be involved. MY
under standing is never ever use the decompression unless hand
cranking on any diesel. Doug
--

:

 

[stevebirch2002]

I must admit that when I had a Volvo MD6A I always
used the decompression lever until the engine was spinning freely then dop it
down. Most of the older Volvo Diesels seem to use this my system.

Steve B
From: Douglas Pollard
Sent: Sunday, October 06, 2013 5:13 PM
To: AlbinVega@yahoogroups.com
Subject: Re: [AlbinVega] MD6A Decompression
Problem
IT's Been my understanding that the
decompression lever should only be used when hand cranking. This is true of most
diesel engines so I have not tried it on my Volvo. IF your starter won't
start the engine with decompression I would say your batteries are low or there
is something wrong with the starter. Possible a bad ground could be
involved. MY under standing is never ever use the decompression unless
hand cranking on any diesel.
Doug --

:

10/06/2013 09:33 AM, bonnerwhitman@...
wrote:

 

[stevebirch2002]

Hi all
 
Anyone need a surveyor for Vegas then contact this
guy, pretty good and knows his stuff:
 

Hi Steve,
 
Thankyou for your
time yesterday morning, If you can add me to any surveyors list you has
as discussed,
 
Ben Sutcliffe Marine  
07796  457307   Ben holds membership of YDSA, IIMS and BMF he has
been surveying for many years. In the 1980’s and 1990’s Ben also worked on
several craft when working at Whistocks boat yard and Anglia Yacht Brokerage,
Marine services. www.bensutcliffemarine.co.uk
 
Thanks hope that’s
ok.
Regards
ben
 Steve Birch
 

 

[dougpol1]

Steve, I am astounded. I never have
understood why that shouldn't be done. I could not see any
difference between hand cranking and starter cranking. Still I
have many times not to use the decompression lever when using the
starter that it may damage the valves. I am not sure I would be
able to bring myself to give it a try??? Doug

 

[bonnerwhitman]

 A bit more info. I went out today and lifted the decompression handle and was able to rotate the wheel with the crank with what seemed to be a normal amount of effort.  So perhaps it is the starter? It is 30 years old, after all.  Thoughts about what to check and how?Thanks!BW

 

[Vega1447]

Presumably people decompress before engaging starter to extend the life of the starter motor?

FWIW my MD6A starts fine without decompression except in freezing conditions.

In freezing conditions I "help" the starter motor using the cranking handle..

Glow plugs would be nice...

John V1447 Breakaway

 

[tiempo2010]

You can use the decompression lever to help start a diesel. either electrically or by hand. Don't ever try to stop the engine with it though. I agree with Doug that if you need to use it there is an issue with the battery/wiring/connections, either bad ground or positive connection or the wire is just too small and old. Most boats have minimal engine starting wire size and if it is old and a bit corroded it is worse. Upgrading the cabling to 1/0 or 2/0 tinned with good connections will make starting faster.

 

[dougpol1]

Man O Man, Do I feel dumb I have believed that you should not use a
compression release to start an engine by starter for probably 30 years.
I have always wondered why people don't question stupid stuff and I had
swallowed this one hook line and sinker. Yukkk ! Doug

 

[chris20636]

I just dismantled and removed a seized up MD7A from my (non-Vega) boat. Once I tried to start the motor with the hand crank just for practice and it seemed near impossible unless one was a weight lifter. Not knowing any better, I assumed this was normal. During dis-assembly I discovered that the rod that is rotated by the lever was broke between the two cylinders. I assume this means only the rear cylinder was being decompressed.