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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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  #1  
Old 02-28-2012
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Volvo MD7a

Looking for owner experiences with the old MD7a. What were the pros and cons of the engine? Did this model have any specific issues? Wish it were fresh water cooled or has been largely irrelevant in your experience? Also looking for experiences with starting this engine in cooler climates. Major pain? Minor inconvenience? No issue?

Thanks in advance.
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Old 02-28-2012
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The MD7a is not a bad engine for its vintage but they are all getting pretty old. Some things to think about:

Very few of these engines have fresh water cooling (usually an owner conversion) and raw water cooling has its goods and bads. It is simpler but there tends to be a lot of buildup in the cooling passages. Every ~10 years, it is a good idea to flush the cooling system with Rhydlyme or Salt Away or one of those products. Removing the thermostat allows some access to the passages also.

Parts for this engine are relatively expensive but in my experience, you need very few of them. In the grand scheme of things, I don't think that this is a huge issue unless you get one where just about everything is worn out. Some of the parts are pretty weird, especially the gaskets for the cooling and fuel system.

Access on this engine can be good or bad depending on the installation. The raw water pump is on the back of the engine and the alternator is on the front. Whether this is good or bad depends on the boat.

This engine is definitely noisy. It is a 2 cylinder with a giant flywheel so the vibration is definitely noticeable but not horendous. The engine itself is noisy and the exhaust is very noisy for an engine this size although you can muffle the exhaust some.

Many of these engines are getting old and have poor compression which can for long cranking times when it is cold. My experience is that cold cranking times are something like 3s for >70F, 6s for >50F, 10s for >40F on an engine with decent compression. The starters are definitely oversized for these engines so as long as you have the batteries, you can crank them a lot.

Given a choice, I would go for something newer but I wouldn't consider one of these a complete deal breaker. While no one ever plans for it or wants to pay for it, if the worst did happen, a Beta marine engine will fit in place of one of these with a little engine bed modification. What type of boat is it in?
jrd22 and eherlihy like this.
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Old 02-28-2012
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Hello Klem,

Thanks for your input.

The boat is a Sabre 28. In both examples I would consider, either the injector system or the engine as a whole has been rebuilt.

It would not be my first choice of engines either. Trying to weigh the engine versus other factors of the old boat which I largely consider positive for my needs at this point. I would prefer not to have to repower, especially in the first season of owning the boat. You're right if worse came to worse, there are always the Beta Marine engines that seem to get good reviews on these type forums. Also, could repower with a rebuilt Yanmar or the like and this would save some $$$ versus the new engine. Then it gets into the issues of the offset prop of the Sabre and the left hand turn of the Volvo versus replacement engines that have right hand turning props. There seem to be varying opinions on these type forums about this issue. I'm not sure how big a deal it is in terms of handling, etc.

If I were to go this route, the boat would be brought from a saltwater environment to a freshwater environment on the Great Lakes where some of the Spring and Fall sails might make for some cooler starting temps. Just trying to weigh it all out.
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Old 02-28-2012
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Will you have shorepower where you keep it? With it, you can make an engine start much easier through several different methods. The easiest is to aim a heat gun at the air intake for a little while. You could also put an oil pan heater on which helps with cranking speed and does heat the block a little. Another option would be to heat the compartment. With all of these you want to be careful about making it safe. Unfortunately, you can't really hook up a conventional coolant block heater on a raw water cooled engine.
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Old 02-28-2012
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Red face Yes there will be shorepower

Quote:
Originally Posted by klem View Post
Will you have shorepower where you keep it? With it, you can make an engine start much easier through several different methods. The easiest is to aim a heat gun at the air intake for a little while. You could also put an oil pan heater on which helps with cranking speed and does heat the block a little. Another option would be to heat the compartment. With all of these you want to be careful about making it safe. Unfortunately, you can't really hook up a conventional coolant block heater on a raw water cooled engine.
Yep, there would be shorepower and those are some options to consider. Thanks.

I think the bigger issue is simply whether or not the engine as a whole is worth the risk given that it is raw water and has spent its life in saltwater. Especially since on a boat of this vintage, an engine repair/replacement is such a large proportion of the overall cost/financial worth of the boat. I suppose the best that can be done is to have a diesel survey and take a chance if I want to go with this boat.

As mentioned, in a perfect world I would prefer a different engine and it has given me enough pause to consider buying other boats with newer engines. Then I have to keep reminding myself I'm not simply looking to buy an engine.
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Old 03-11-2012
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Re: Volvo MD7a

I have a vintage 78 MD7A in my Newport and I am in a cooler climate (northern Idaho...) so I know of what you speak. Mine cranks quite long if I am starting it after being idle for a couple of weeks...but as long as I crank it over every week it does just great. the key on the MD7A that I found is to make sure your throttle is at least 2/3 forward and if it doesn't catch within about 6-10 seconds, back off and try again. I have had to resort to starting fluid when I have laid her up for over a couple of weeks, but if you use it sparingly, she fires right up. Klem is certainly right about the noise and the vibration...even with new motor mounts she shakes and dances...and a loose engine access hatch adds to the noise. The thing about the old Volvo's is, if the compression is good, they are as dependable as you can get, with very little maintenance. We have several older boats in the marina with D6's and D7's and we all swear by them...as far as heating it up, a crankcase heater (dipstick style) will help if you have shore power.
Ed
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Re: Volvo MD7a

Ed,

Are you sure that you don't have a very small air leak in your fuel system? From the engine's prospective, there is no difference between sitting for a week and 2 weeks. After a day, the engine block will not retain any heat and nothing should change so starting should be the same provided that your batteries are not discharging.

If you want to test for an air leak, let it sit for 2 weeks and pump the hand primer for a long time before trying to start it. If it starts similar to sitting for a week, you have a small air leak. This will not rule out an air leak in the injection line but it will get most of the likely suspects.
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Old 03-12-2012
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Re: Volvo MD7a

Fit a 235AD...

Electric Fuel Pumps - Stewart Warner

...to pressurise your fuel system and you will never have an air leak again. If the fuel system leaks, you will see the diesel dripping out and you can fix it.

The motor is sound, and oversize pistons were available from Mahle in 1998 and probably still are. Two pistons will cost about £100 each, and a top end gasket set about another £100. Reboring the two barrels would cost about another £100.

You could re-cut and re-grind the valve seats also.

You don't even have to take the motor out of the boat to do it.
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Old 03-15-2012
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Re: Volvo MD7a

Klem,
I haven't checked to see if I had an air leak in the line...to be exact, I have never thought that might be the issue...it has always acted like that since I bought the boat and I have always just worked around it...I'll have to check it next time I am up to the boat...
thanks...
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Old 03-30-2012
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Re: Volvo MD7a

I also have a Sabre 28 w/ the MD7A & have spent a bunch of time looking into what's out there for repowering if the need arises. You can get a Yanmar w/ a ZF transmission & this will addresse the LH rotation issue of the Volvos.

Never use starting fluid on a diesel, try WD-40 instead, much safer & it won't destroy the motor.
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