Rebuilding the Volvo MD7A

[Compass790]

Originally Posted by Zekmeister

I'm actually looking to see if its worth converting to freshwater cooling and if the conversion kits are still being sold.

Just a comment on converting to fresh water cooling. I completely rebuilt our 1980 Yanmar ysm8 raw water cooled engine & flirted with the idea of doing a fresh water conversion. However after descaling the head & block I thought why bother? It was like new underneath the scale. Figured if it can do 37 years no problem who cares if it's raw water cooled. As long as you keep the anodes up to scratch no problem I think.
Fresh water cooled engines are supposed to be more efficient as the operating temp is better but I couldnt get too excited about that either as we only burn about .75 litres per hr. Just some thoughts for you to consider.
Good luck with rebuild, it's a great way to learn every part of your engine & help with fault diagnosis

[MicHughV]

...I feel compelled to chime in here.
Back in the late 70's/early 80's I built a steel Roberts 38.
Being dirt poor at the time, the only diesel I could afford was the Volvo MD7....if memory is correct, it was the MD7B model, same as the MD7A model, but had an unusual feature at the time, which was a downward angled gearbox, which assisted my installation.

Raw water cooled, very unusual, producing around 17 hp or so.

It could be started with a hand crank and the two cylinders were fitted with a de-compression lever.

Being raw water cooled in a salt water environment was unusual, nonetheless, that is what it was.

It was about as basic a diesel engine as one could buy. It had a monster flywheel.

True, Volvo diesel parts are prohibitively expensive, but spares abound, you just have to search the internet.

I had that engine in my boat for around 10 years or so and did just fine with it. A bit slow, sure, but always got to where I was going.

I found oil filters at an Auto Parts store and other other odds and ends elsewhere.

One time, I had water come into the engine, a long story. The pistons (only 2 of them) completed seized up. I removed the head and beat on the one piston that was near the top of it's stroke with a piece of wood and a sledgehammer until it reached the bottom of it's stroke, put everything back together again, and son of a gun, it fired right up.

About every two years or so, I would remove the cylinder head and ream out the cooling orifices around the cylinders and elsewhere. After about two years, those orifices were pretty closed up from the salt water. I didn't even replace the cylinder gasket....just put everything back together and it would start right up.

It's a helluva tough engine.

I had really only one bitch about it. It had these very unusual pipe fitting rubber gaskets, which were a bitch to find and install correctly, especially around the seawater impeller. I ended up sawing all the various tubing ends off and replaced them with a rubber hose and clamp where I could.

For it's horsepower rating ( around 17) it is a heavy engine...close to 400 lbs.
They quit making these engines now.

I later replaced it with a Volvo 2003 series engine....27 hp and 3 cylinder.
Also, out of date now, but spares for both engines can still be found, especially so, if you have a Volvo dealer in your neighborhood.

Failing that...try Craigslist and other internet sites and you will be surprised at the number of these engines that are still around.

Failing in that, if it was me, I would replace with a Yanmar diesel. Like the MD 7 series, check out the internet. Much lighter, more reliable and less expensive to install and maintain.

Just my 2c.

[Compass790]

Reading MichughV's good post maybe the volvo is more susceptible to scale buildup than the yanmar. There are ways to descale in situ, check threads on that. Mind you we always fresh water flush ours after we return to marina.
Maybe you should do that too.

[MollyJo]

Originally Posted by Zekmeister

Thank you. How much do you want for it?

How does $50au + post sound?

[Zekmeister]

Originally Posted by MollyJo

How does $50au + post sound?

OK. How much post to US zip code 92592.

Thanks

[Zekmeister]

Originally Posted by Compass790

Reading MichughV's good post maybe the volvo is more susceptible to scale buildup than the yanmar. There are ways to descale in situ, check threads on that. Mind you we always fresh water flush ours after we return to marina.
Maybe you should do that too.

Flushing with freshwater after each run definitely.

[Zekmeister]

Originally Posted by MicHughV

...I feel compelled to chime in here.
Back in the late 70's/early 80's I built a steel Roberts 38.
Being dirt poor at the time, the only diesel I could afford was the Volvo MD7....if memory is correct, it was the MD7B model, same as the MD7A model, but had an unusual feature at the time, which was a downward angled gearbox, which assisted my installation.

Raw water cooled, very unusual, producing around 17 hp or so.

It could be started with a hand crank and the two cylinders were fitted with a de-compression lever.

Being raw water cooled in a salt water environment was unusual, nonetheless, that is what it was.

It was about as basic a diesel engine as one could buy. It had a monster flywheel.

True, Volvo diesel parts are prohibitively expensive, but spares abound, you just have to search the internet.

I had that engine in my boat for around 10 years or so and did just fine with it. A bit slow, sure, but always got to where I was going.

I found oil filters at an Auto Parts store and other other odds and ends elsewhere.

One time, I had water come into the engine, a long story. The pistons (only 2 of them) completed seized up. I removed the head and beat on the one piston that was near the top of it's stroke with a piece of wood and a sledgehammer until it reached the bottom of it's stroke, put everything back together again, and son of a gun, it fired right up.

About every two years or so, I would remove the cylinder head and ream out the cooling orifices around the cylinders and elsewhere. After about two years, those orifices were pretty closed up from the salt water. I didn't even replace the cylinder gasket....just put everything back together and it would start right up.

It's a helluva tough engine.

I had really only one bitch about it. It had these very unusual pipe fitting rubber gaskets, which were a bitch to find and install correctly, especially around the seawater impeller. I ended up sawing all the various tubing ends off and replaced them with a rubber hose and clamp where I could.

For it's horsepower rating ( around 17) it is a heavy engine...close to 400 lbs.
They quit making these engines now.

I later replaced it with a Volvo 2003 series engine....27 hp and 3 cylinder.
Also, out of date now, but spares for both engines can still be found, especially so, if you have a Volvo dealer in your neighborhood.

Failing that...try Craigslist and other internet sites and you will be surprised at the number of these engines that are still around.

Failing in that, if it was me, I would replace with a Yanmar diesel. Like the MD 7 series, check out the internet. Much lighter, more reliable and less expensive to install and maintain.

Just my 2c.

I'll putter around with the MD7A for a few years hopefully and by then electrical propulsion would have matured enough to convert to.

[Zekmeister]

Originally Posted by Compass790

Just a comment on converting to fresh water cooling. I completely rebuilt our 1980 Yanmar ysm8 raw water cooled engine & flirted with the idea of doing a fresh water conversion. However after descaling the head & block I thought why bother? It was like new underneath the scale. Figured if it can do 37 years no problem who cares if it's raw water cooled. As long as you keep the anodes up to scratch no problem I think.
Fresh water cooled engines are supposed to be more efficient as the operating temp is better but I couldnt get too excited about that either as we only burn about .75 litres per hr. Just some thoughts for you to consider.
Good luck with rebuild, it's a great way to learn every part of your engine & help with fault diagnosis

Thought about this too. But kits are hard to come by and they're expensive.

[MicHughV]

...reading thru' this thread again...my Volvo MB7B fuel consumption was miserly....again, if memory serves me correct....about .3 US gallon per hour and this at around 2,200 rpm or thereabouts.
My cruising speed, pushing a 20,000 lb boat was around 5 knots, maybe 6 in a flat calm...I don't remember the prop size....it was a narrow 2 blade design....15" maybe...17"...I don't remember anymore. When I was sailing, I would rotate the prop shaft so that the blades aligned with my keel for less drag.
Diesel science is a long arduous road. Boat displacement, waterline length, type of underbody, type and size of prop, aperture clearance, reduction gear, etc, etc...
It didn't take a lot of horsepower for my boat to reach 5 knots, but to reach 7 knots, takes 3 or 4 times the hp.
There is an excellent book available called " The Propellor Handbook" by " Dave Gerr". In it, you will find everything and anything possible about diesel engines, props, boats, etc, etc. It's a very comprehensive book. and I can highly recommend it to anyone in the boating business.

[hpeer]

I also have an MD7A in my 16,000#, 33’ steel cutter. It’s got about 600 hours on a rebuild by the previous owner. As above it gets me around and is stingey on fuel.

I also hate those water fittings. You know the o-rings? I went to a Home Depot with an old one and found a common faucet o-ring the exact same size.

A few years ago I picked up a MD7 sitting in a yard for $250 and a two day drive. One cylinder had some moisture and light rusting around the rings. Initially I was able to move the flywheel but then it siezed. So I took the head off and, as above, drove the piston loose with a bit of wood and a hammer. By hand it has some compression but not much.

Maybe someday I’ll get it rebuilt if my working engine starts to give me fits. That would give me a drop in replacement. What I don’t know is if this spare engine has been rebuilt before. Somehow I doubt it.

Replacing these engines is a bit more expensive than it might seem at first. I looked at a Beta/Nanni. Right hand drive vs left. Exhaust in wrong side. And I think there were issues with the water supply also, can’t recall. So the whole engine compartment needs to be redone.

But when you factor all that in the cost of a rebuild starts to look attractive.

[MollyJo]

Zekmeister, Sorry for the delay
I had to find time to get to the post office. Looks as though $15 will cover postage. Let me know by private post if you decide you need it.

[Shawn67]

Originally Posted by Zekmeister

I'm actually looking to see if its worth converting to freshwater cooling and if the conversion kits are still being sold.

Former MD7A owner... you don't need a kit. When I had my exhaust manifold off to clean it out (citric acid soaks and wires in probing the passages) I converted to fresh water cooling.

Basically you need an appropriate sized heat exchanger and a pump. At a marine consignment store I found a used exchanger off a 14hp Yanmar for around $150.

The raw water pump is made by Johnson. If you have the version with the slots in the stem of it (not just the weep hole) there is a Johnson part that replaces the existing cover and makes it a double pump. The original side becomes fresh water and the add on pump is for raw water. You then just plumb the fresh water side of the heat exchanger between the inlet to the tranny and the output from the thermostat housing.

From your strainer you go into the secondary pump, through the raw water side of the heat exchanger and then into the exhaust injection point.

I posted some more details on this here.

Shawn

[Shawn67]

Originally Posted by MicHughV

I had really only one bitch about it. It had these very unusual pipe fitting rubber gaskets, which were a bitch to find and install correctly, especially around the seawater impeller. I ended up sawing all the various tubing ends off and replaced them with a rubber hose and clamp where I could.

For those that need them these are available at West Marine. https://www.westmarine.com/buy/sierr...ives--10511004

The description is wrong, these are the parts for the MD7A.

Shawn