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Old 12-10-2014, 16:28   #1
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Volvo Md7a Rebuild or Repower

I had a leaking head gasket that over heated and filled the rear cylinder with water so it would not start. I pulled the head, had the head machined, replaced the head gasket. It starts now but with white smoke and will not go over 1100 rpm in gear. Any ideas?

The bigger question if the mechanic says it needs to be rebuilt.. Should I rebuild or repower with a beta 16?

Back ground info - My boat with a working engine is worth $17k. The md7a is raw water cooled. The rust and corrosion in the water channels are limited. When I had the head off I was surprised how good it looked. I have a friend that will help me assemble so I will save on labor. I also rebuild the following over the last 1.5 years - exhaust elbow, water pump, fuel pump, injector pump, injectors serviced.

Thanks for your input. I know the general thought is to repower if raw water cooled. But I rebuild so may items.


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Old 12-10-2014, 17:16   #2
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Re: Volvo Md7a rebuild or repower

Have you got a quote on a rebuild?

I have a good runner but did consider a new engine as I had the engine out over the winter. But when I looked at ALL the costs I really want to stay with the MD7A.

Besides the engine proper.....

The exhaust comes out the port side.....have to rejigger the exhaust run.
Right hand prop vs left hand prop, need new and bigger prop. Maybe shaft also if it is too short?
Change engine mounts.
Likely need to change engine controls.

I managed to find a spare MD7a for a good price, don't know if it's a runner or not. But I've now got lots of spares at least.
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Old 12-10-2014, 18:33   #3
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Re: Volvo Md7a Rebuild or Repower

Has your prop built up a large collection of weed and hard things during your down time? That might explain the low RPM. Have you done a compression check since the rebuilt head went back on? Also, even if your injectors were rebuilt recently, you might want to have them pop tested, since the overheat, or a spot of rust could have buggered one of them.White smoke would indicate a fuel problem. Do all kinds of things before you go to a re-power. Best of luck. ______Grant.
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Old 12-10-2014, 18:46   #4
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Re: Volvo Md7a Rebuild or Repower

I got a quote for a repower - $10-11k with me doing most the work. No quote on a rebuild.

I thought about the build up on the prop, but I thought that over loading should be black smoke vs white. Besides I have bottom cleaning every month.

I had the injectors tested - they are okay.

I will ask the mechanic to do a compression test before I do any thing.


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Old 13-10-2014, 10:41   #5
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Re: Volvo Md7a Rebuild or Repower

Well what goes round comes round. I had a similar choice a number of years ago. Our problem was I knew our MD7 engine needed rebuilding when when started to have transmission difficulties which nooen could solve. I took the unit off the engine and ended up at a dealer in Toronto. The mechanic therre was baffled , but by sheer chance, a Volvo mechanic from Sweden came in to visit on a bus man's tour. He knew exactly what the problem was and fixed it in about five minutes. I told him about my issue of rebuild vs replace and he sail something like " this is the best engine Volvo ever made bar none. Rebuild it and it will outlast you". So I did. Had some difficulty with specialized tool but solved that by modifying other tools. His words were totally accurate. We had far more power than we had ever had and the engine ticked along for ten years until we sold the boat. The new owners dropped in to see us about five years later and it was still running like new. Rebuild it. You'll have the advantage of knowing the engine intimately and you'll never need to hire a mechanic who will charge you mega bucks while he learns his trade on your motor. Cheers
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Old 13-10-2014, 18:46   #6
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Re: Volvo Md7a Rebuild or Repower

Dancer, do you happen to remember what the little trick was that fixed the transmission problem? There are more than a few ears, and eyes that always want to know how to solve Volvo problems. _____Grant.
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Old 18-10-2014, 21:46   #7
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Re: Volvo Md7a Rebuild or Repower

Update - tried doing a compression test today, but I did not have the penta fitting. I got a 220 psi reading but it should be 280. The difference could be because my fitting was jimmy rigged. I determined the smoke was mainly steam. I have no idea what to do next.

Revised question.... What is everyone thought about scrapping the boat vs repowering for $11k. The boat is a 30' islander in good condition, so worth $15-20k w/ engine. I think I could scrap her for $3k.

Money now is tight... So the idea of 10k into a new boat may be better.


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Old 19-10-2014, 04:22   #8
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Re: Volvo Md7a Rebuild or Repower

11.000$??

I guess you could have a rebuilt engine shipped from sweden for a lot less..
If it was me , I would get a freshwater cooled md7b base engine. and keep your rebuilt externals.

MD6/7 engines are well known for being close to indestructable.

David in goteborg is the one I would call.

https://translate.google.no/translat...%2F&edit-text=

.manitu
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Old 19-10-2014, 06:08   #9
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Re: Volvo Md7a Rebuild or Repower

Shop around. A B16 should not be this expensive. It is just a tractor engine. They are said to be good horses.

I would rebuild, if this makes economic sense. We have an MD7 here too and it too lacks somewhat. We will be at your decision point somewhere down the road.

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Old 19-10-2014, 11:56   #10
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Re: Volvo Md7a Rebuild or Repower

Jeff, does the white smoke start as soon as you run the engine, or only after it heats up? Is the engine actually overheating? Is your temp gauge working? A test that may or may not have any value, would be to pressurize your raw water passages, and see if they hold pressure, or leak down. It would be difficult to do with the Md7 because of the slip joints in the system, but with some extra copper tubing, and plenty of slip rings, you could put 10 or 15 PSI into the system, and see if there is a leak that cant be seen from the outside. If you try this, do it after the raw water pump, and before the exhaust injection into the manifold. Ask the machine shop that did your head, if they pressure tested it? A good machine shop usually will, but not always. Have you used an IR hand held thermometer to determine which cylinder is not running correctly? You have had most of the major(expensive parts) parts rebuilt, and short of a cracked head, or rust hole in the block, I think a rebuild would make more sense than a replacement. Since you are probably going to do another compression test, you might want to try hooking your injectors up to the lines when they are out of the head, and turning the engine over to see if they shoot a nice spray , or if one is different than the other. Be very careful, since the spray can cut through skin or ruin eyesight, but it is not really difficult to do. Also put an old towel over the head so that nothing sprays out of there when you turn the engine. I wish you luck. This sounds like a mystery. ______Grant.
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Old 19-10-2014, 12:03   #11
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Re: Volvo Md7a Rebuild or Repower

Jeff, just went over the thread again, and the question of black smoke versus white smoke. Normally a bad running cylinder , or a faulty injector will give you black smoke, but if the cylinder is completely dead, but fuel is still being sprayed into it, the fuel can vaporize(but not burn) and come out the exhaust as white vapor. It would smell highly of diesel, so would be easy to detect between steam, and fuel. Just another thought. _____Grant.
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Old 19-10-2014, 14:20   #12
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Re: Volvo Md7a Rebuild or Repower

jeffjd,

For my 2 cents- rebuild if needed.You're overlooking something with only getting 1100RPM. You'll find it.

My reasons are- you've got a bit of $ into vessel,you'll never see the $ back from new repower when you sell. Enjoy your boat


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Old 19-10-2014, 14:51   #13
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Re: Volvo Md7a Rebuild or Repower

Will it go over 1100 rpm in neutral?
Not sure why thinking of rebuilding or replacing with a problem of not reaching rpm. Seems to me you must have another problem. My experience says once you get a worn engine started it will go to rpm... even if it smokes a lot. Maybe the wet cylinder does have frozen up bad rings... then that would make sense. Try cracking an injector nut while it's running and see if that cylinder is making power... 280 psi isn't a very high goal for a diesel.... maybe the Volvos are lower I guess..
Is the head is rebuilt..? or maybe you just ground it flat? The old Islander is likely not worth a new diesel... unless it's perfect and you intend to keep it a LONG time....
There's always an outboard bracket and used 10hp kicker .. all for under $1k...
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Old 19-10-2014, 15:58   #14
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Re: Volvo Md7a Rebuild or Repower

This thread is really good, it has raised a few questions as I have a "spare" in the basement.

The OP noted he put oil on the top of the expose cylinder and it ran into the crank case over some period of time. Should the oil not run past the rings over say 24 hours?

How are the cylinders rebuilt? I understand you can turn them down at least once. Can the liners then be replaced?
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Old 19-10-2014, 16:17   #15
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Re: Volvo Md7a Rebuild or Repower

Thanks for all comments.

I am pretty sure my white smoke is actually steam. I put a cup over the exhaust and condensation formed in 20 seconds. The white smoke starts right when the engine is started and will continue after it gets to operating temp. It does not run hot. About 140. I have tested the temp gauge in the past with IR and it checked out. In addition to the steam, black soot is present in the water.... If I lower the swim ladder to will have black soot within 20 seconds.

Once warmed it will get to 2500 rpm out of gear, but only once it is warmed up. It is like the throttle doesn't matter when it first starts. In gear only 1100rpm at 1/2 throttle. Full throttle runs a little worse.

Starting cold it will that takes 20-30 seconds to start and it hardly starts. Once warm it will start in a few seconds.

I thought it may be the lift pump so I check the fuel return and it has a constant flow. I read somewhere the it the lift pump was bad or if clogged filters the return fuel line would be dry.

My current thought is that when I replaced the head gasket I did not get a good seal somehow. From my understanding this could explain the steam. But I don't know if it explains the lack of power or soot.

Without an adaptor for the injector sleeves I know my compression test is close to worthless. (I rigged a rubber seal and held it in place) The only value is the they were consistent between cylinders.


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