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Old 13-05-2020, 14:36   #31
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Re: MD7A Exhaust Manifold Mystery Hole

**** man, just made a thread just like this. Haha we need answers, I really don't want to end up putting it back on like you did, but i guess if it's fine it's fine...
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Old 14-05-2020, 07:31   #32
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Re: MD7A Exhaust Manifold Mystery Hole

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Originally Posted by SkydivingSailor View Post
**** man, just made a thread just like this. Haha we need answers, I really don't want to end up putting it back on like you did, but i guess if it's fine it's fine...
who are you addressing? I opened that port up, nothing changed and everything is working fine. I don't think it was necessary. The temperature is the same as it was before I worked on it. If I were to do it again I would leave it plugged.
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Old 14-05-2020, 07:36   #33
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Re: MD7A Exhaust Manifold Mystery Hole

Ahhhh sorry I'm dealing with another hole---is there any chance you can tell me if my understanding of this manifold is correct? https://www.cruisersforum.com/forums...99#post3138999


I tried to make diagrams, would love your input if you have a minute!!!
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Old 14-05-2020, 07:43   #34
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Re: MD7A Exhaust Manifold Mystery Hole

Thought I was clear enough in my previous posts above.

Don’t screw with it. It came from the factory like that so just leave it alone. I have TWO MD-7A motors, one on the boat, one awaiting rebuild. Both manifolds are identical to hours and other posters.

Someone else did open it up and it didn’t hurt.

Clearly you don’t have enough to worry about. LOL.

Put some energy into finding a replacement mixer elbow. That’s a toughie.
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Old 14-05-2020, 08:04   #35
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Re: MD7A Exhaust Manifold Mystery Hole

Haha appreciate the advice man. My mystery is, where does the water that flows into the mani from the bottom go?


To clarify, the copper water rail connects to the mani in two places. One of the places is the thermostat housing, and the flow is clear. The other is connects to the the bottom of the mani itself, and I can't figure out where the water should go
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Old 14-05-2020, 08:40   #36
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Re: MD7A Exhaust Manifold Mystery Hole

Not sure if this is helpful or not. I had my MD3 overheat. Found blocked and hidden passages in the exhaust manifold. A large passage feeding two small passages. The large one was the inlet and only partially blocked. After removing the manifold it took 7 days of filling the passages with muratic acid, giving the acid 30 to 60 minutes to work (it stops foaming) then using a stiff wire to dig open the blocked passages. The small blocked passages were at first hard to detect the crud fill them so perfectly. Once everything was cleaned out, cooling back to normal.
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Old 14-05-2020, 08:51   #37
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Re: MD7A Exhaust Manifold Mystery Hole

Yup, I appreciate the question. I just don’t know how to answer it. So I set out on a long trip last summer, where I really needed the engine. And it crapped out. Over heated, after running cold for a couple of days. Some things you just can’t figure out.

So the manifold comes off and, not knowing what else to do, I just start poking at it with pointy things. I think I cut like 6 inches of Small wire rope and chucked it up in a drill and used that to get Into various places. Dental picks, etc. Just keep poking around trying to figure out where the water goes. There are internal passages that are not obvious.

After a while I kinda got to where I could feel the difference between the base metal and the crud. Lots and lots of patience, and beer, beer helps.

I then poured water in so I could see where it ran out. And I then taped over various ports so the manifold would hold water. Then i put in Ospho and let it sit. For a few hours. Go to the club house, have a cuppa, swap lies. Rinse out the manifold, run water through. Dig out what ever is now loose. Tape it up, pour in some OSPHO go to the club house, etc. The trick was to wait until it would quit off gassing. Then you have the crud out.

THen I reassembled and put some Ospho in a bucket and ran a hose from the thermostat housing back to the bucket. Then open the decompression lever and pump some Ospho through. At first it would off gassing pretty good, the line from the thermostat into the bucket would bubble. We think I did this about 3 times until it quit bubbling.

That seems to cure the problem, after that she was making good water. I did a test of about a half hour, ran her hard up to temp. I could see the thermostat cutting in and out. Then I had to pull her to do some work on the hull.

Anyway, that’s what I did. Lots of patience picking around, and beer.
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Old 25-05-2020, 22:02   #38
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Re: MD7A Exhaust Manifold Mystery Hole

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Originally Posted by jeffjd View Post
Head work costs $750- $800

The machine shop was $250. They welded the Head where the water created a channel, cleaned everything up. Deck the head to make sure it was flat. Ground the values and reset them, and replaced the injectors sleeves.

They also put Heli coils in the exhaust manifold where the thermostat housing bolds it. This was worth the $50, because about 1/3 of the threads were left.

Parts cost about $500 and included.
Cam seal $45 was leaking
Head gasket $120
Injector sleeves $100
Exhaust gasket $45
Other gaskets and seals $35
Other parts, lube, rags, washers, bolts, jb weld for the channel on the block $60
Shipping $60 (three shipments)

Engine starts with lots of smoke, but I am dealing with water leaks between the water pump and thermostat housing. So it has only run for a couple minutes. I had to call it a day and will fix the water leak in a few days.

I don't know if there is a trick, but lining up the pipe from the raw water pump is difficult without creating leaks... I did it before when I rebuilt the water pump.


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Hi
I recently cleaned out the exhaust block and elbow and then when put it back together had problems with leaks - I am down to 2 connections fixed (end into water pump and end into thermostat housing)but connection into the block still to deal with. It keeps popping down. My plan is to wedge it up somehow (maybe wedge some heat proof material under the pipe) and tie the end in at the water pump (so it does not pop out when I push the other end in) in with 2 clamps over a split piece of rubber hose.
Hope this makes sense.

Also the exhaust block has a closed over circular bit that does not seem right since the gasket has a hole there.
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