Volvo Md7a Rebuild or Repower

[hpeer]

The PO had my MD7 rebuilt just before I bought the boat.

I found the invoice which listed all the parts used and the hours billed.

Posted just because I thought you might find it interesting.

[gjordan]

Hi Greg, I havent pulled the pistons yet to do a ring and bearing job, but that wont take too long after I find some affordable aftermarket parts. I bought an MD6B just to get the transmission, but between your engine, and spare Parts, plus the parts that are inter-changable from the MD6 and what I am learning from this thread, I feel very good about this engine for the long run. The deal on the boat that I thought I had lined up fell through, but I will be looking in the same size range, and with my budget, it will probably come with an old rust bucket Anemic 4, so I will more than likely get lots of use out of your old engine. Again, thank you for being such a fair person to deal with. ______Grant.

[jeffjd]

Greg

I think the repower option is the best idea... It is just money is tight now. So I hope to get the md7a running okay and then repower another year.

I plan on going with the beta 16. It was good to hear you picked up 2 kts.




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[weephee]

I checked the rod bearings I have and the only mark is on the outside of the bearing and it is STD. and a funny little sympol just under it. No numbers or marks on the inside or on the edges. Anyone have any luck in finding non volvo rings for the md7a
Larry

[gjordan]

I discovered another thing about the MD7. In looking through the various Volvo parts sights , there were apparently MAHLE marked pistons, and pistons with just a Volvo part numbers. There was no indication of different ring numbers, so they may be identical. I didnt intend to start on my engine until after Xmas, but I may pull both of them apart this week to see if I can learn anything about the rings, and the bearings.______Grant.

[jeffjd]

After the compression test checked out I figured a sea trial was in order. I estimate the engine produced only 1/4 the normal power. I double checked the prop and it was clean.

So I decided that I should get the injector pump and injectors checked out. I removed them and will take them to the shop today. It has to be a fuel issue as it is not burning all the fuel.

Because I reused the head gasket I also pulled the head to put a new gasket on and surface the block. Check out the build up after only 2-3 hours.

Does anyone know how to check the injector timing?

Any other ideas if what can cause reduced power?


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[hpeer]

It's on page 28 pf the shop manual.


http://www.bluemoment.com/manuals/Vo...A_Workshop.pdf

[hpeer]

Groping here.

Do you have free flow of fuel to the engine? To the pump?

Could the return banjo fitting have muck in it? Mine had what appears to be a slit/split pin inside.

Does the engine sound OK? Possible bad shaft or bearings?

Transmission dragging? Does it rev up in neutral, forward, reverse? 2,500 rpm.

Sorry if you stated some of that already.

My guess is something with the pump, but only a guess.

[jeffjd]

The prop shaft spins freely by hand when out of gear. So I think I am okay there.

Transmission dragging - what do you mean?

I will inspect the banjo bolts closer.

Pump is at the shop so I will know one way or another. He thought it is most likely fuel supply pre pump.

I am really getting to know this engine.


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[hpeer]

Transmission dragging.. IIRC you should be able to turn the engine over, by hand, no compression, with the transmission in forward or reverse.

Just to make sure the transmission is turning freely.

As said before, just grouping for easy things to check that are not the pump.

[gjordan]

Jeff, I think you already have an IR thermometer. If you go out for another run, test the tranny temp. If it is friction in the transmission, it will be hotter than a pistol. If it is normal temp, then move on to other possibilities. I still wonder about clogging in your exhaust system? As the saying goes, KEEP ON PLUGGING. ______Grant.

[jeffjd]

Grant

Over the weekend I connected a water hose to the lift muffler to flush the system. It flushed out a some soot and was free flowing. I don't think there is any blockage. Give the significant soot in the head and piston I am thinking it may be a injector issue..... I hope.

Side note - after I get this issue solved I will have to post a summary so the next guy will not have to read a 100 posts to understand the issues. Also I plan on starting a md7a thread dedicated to part sourcing and known fixes. Solutions only.... Without all this searching for solutions..... When I get her fixed.


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[glenn.225]

From the look of that head, I would almost certainly say it is a fuel problem. It’s running far too rich, either the fuel pump is delivering too much fuel or more likely, the injectors are not delivering it properly. I would suspect the injector tip orifices are worn which could have been caused by normal wear or water in the fuel. This is causing a poor spray pattern and insufficient atomization thus incomplete combustion. Or it could be internal wear in the injector letting fuel leak down which would show similar results. I’ll bet you’ll get a bad report back on those injectors and new or rebuilt ones will make her sing. Not sure on how the pump is timed but make sure you get a manual and have it 100% right before you try to start it. Nothing worse than a diesel running away, make sure you have some way to cut off the air to the engine just in case. Good luck with it, it’s been a long haul.

[jeffjd]

Update -

The injector pump checked out okay, but the injectors tips were off, so the shop rebuilt them.

Now the engine has more power (about 75%). I can get the boat to 4 knots in on glassy water. Prior it was 5.5knts on glassy water.

But.... there is a lot of gray smoke. I let her run for 1/2 hour under load and no change. The smoke starts instantly on startup and increases with RPM. I am running out of things to check or change.

I did a compression test and it was 340 PSI, so I have ruled out rings.

The prop is clean, but is not glass smooth.

The transmission was hot to the touch after running under load for 45 mins.

I checked the valve lashing and they were .05mm of too large. I adjusted to the correct amount with a warm engine.

I bypassed the fuel tank and used new fuel and there was no change. I replaced 60% of the fuel hoses. I need to order the other hoses and new crush washers from volvo to have a complete new set.

The injector shop thought I was getting limited fuel and this would explain the lack of power. But this does not explain the gray smoke.

I rebuilt the lift pump. I could have screwed the rebuild up, but I do not know how to test the lift pump.

My current plans are to:

Go back to a Fram P8043 fuel filter vs. the wix filter. I doubt this will do anything but it is a new variable.

Play with the timing of the injector pump. Any tips? Can a valve job or new head gasket require different timing?

Any other ideas are welcome or if you think I might have missed something.

[Cheechako]

I don't know about the Volvo transmissions, my Hurth ones ran very hot... too hot to touch for sure. I swear you could fry an egg on them.....

I cant remember.. too long a thread... is this fresh water cooled or raw? That buildup inside the head is a lot for a couple hours running.
I think it was suggested early on (?) you should try an electric fuel pump. Did you? it's handy for bleeding anyway. Just put it in line near the tank with a switch adjacent.