My old MD7A again......

aquaholic

aquaholic

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The saga continues......forgive me for sounding stupid but prior to me purchasing this boat last year I have never owned or had experience with a diesel engine, now I noticed that if I briefly bought the engine up to full revs she would chuck out black smoke and a different exhaust smell, so i dont make a habit of doing this. However over the weekend this chap at the marina reckons that these diesels need a good pounding from time to time and recommened that i give her a good run, so off i went and slowly built her revs up and ran her for around 20 minutes at full bore, initially the smoke was fairly thick black but after a while it seemed clear and managed to get her up to 6.5knts which she maintained, was this the correct thing to do or was it fool hardy?

I now have new found confidence in this old engine and think that my ideas about re-engining were a might premature.
Fingers crossed.................
 
Older diesels run happiest at constant revs, close to their full power. Black smoke may indicate a worn exhaust valve guide, as leaking oil will find it's way into the exhaust manifold. Any lubricating oil leaking past the inlet manifold or indeed past the piston will be burnt in the combustion chamber. Is the engine using oil?

Diesels do smoke a little when cold anyway and the MD series take a lot of warming up, as they are big old beasts. Even my new 1GM10 smokes a little when cold, although it warms up fairly quickly.

Speaking from memory, some parts are unobtainable. The worst problem being the exhaust manifold. The mixing elbow can be fabricated, as long as you keep the old one to provide a pattern for the flange. If you can find Gasket sets buy one or two as I've a feeling these are a problem, too. Paper gaskets can be made, the paper being available from most good motor factors but the head gaskets are something else.
 
It looks as if the engine is good for a few years yet. I only replaced mine as I couldn't get all the bits I needed (which included the manifold). I'd have one of them fabricated if i was faced with the problem today.

Apart from Cylinder head gaskets and manifold gaskets, everything else ought to be repairable. Until a couple of years ago I kept the old engine in case someone needed parts but it went to the skip when I turned the shed into a propper workshop.
 
All Topcat's remarks apply IMHO. When starting from cold, black smoke and even a little oil leaving the exhaust is normal for the MD7A. The engine has to be run for a while on full power regularly. The exhaust elbow is indeed a problem. I had a boat with this engine a few years ago, and then SS exhaust replacements were to be had from a firm in Norway. However, a friend of mine replaced his by removing the elbow proper from its threaded fitting (well...I did it for him). As this is a standard size, he replaced it with an elbow from a different make (Yanmar?), and it did work out well. The engine is quite simple , get the workshop manual from the web.
 
I had a MD7A for 12 years in a Sigma 33 and it really has to be treated quite badly to get the best out of it.. The occasional blast at full power seemed to clear out a lot of gunge from the engine and remember to use the most primitive engine oil you can get.. The modern oils contain lots of detergent stuff which wash away all the tarry deposits which seal up the piston rings so effectively.( look on the can for the API classification API-CD is good but CG and CI are not). Keep us informed
I like to hear about the everlasting MD7A. It would be interesting to find out who is running the oldest one ---easily 30+years?
 
Mine is 31 years old, I'm sure not a record but not bad.

She puts out a small amount of white smoke most of the time (particularly visible at night with the stern light on) but not, that I have noticed, blue or black.

Are there any risks associated with running the engine at full revs or should it be perfectly safe?
 
[ QUOTE ]
Are there any risks associated with running the engine at full revs or should it be perfectly safe?

[/ QUOTE ]You're obviously loading everything more than if you're just pottering along so, from that point of view, things are more likely to fail at full throttle than when pottering along but, provided the governor is working correctly so the engine doesn't over rev and you watch the temperature, IMHO, anything that does fail would have been close to failing anyway.
 
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