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4.3L Merc Exhaust Conversion!?

1

1marc1

Contributing Member
So I have had some horrible luck over the past year with my boat engine.......we finally put a new rebuilt long block back into my boat and upon bolting my old exhaust on (single piece still) i noticed on one of the driver side manifold that it had 2 holes that were nice and black and one front hole that was showing a fair amount of rust in. Now the hole that was showing rust in, i had zero compression on that cylinder on my old engine which was why I replaced it. So I'm pretty hesitant obviously bolting these old manifolds back on.

I see that there is a new 2 piece conversion system i can do but there is a dry joint and or a wet joint i think i can choose from as well. I have read the dry joint is better but im assuming it costs more. And between the new long block, and a local boat repair shop taking me for over $1000 replacing my fuel system for no reason instead of trouble shooting and not doing a compression check and fuel pressure checks and stuff like that. Im into this boat repair for far more than i would like to be right now. My intention is to sell this thing as soon as i get it back up and running. But lucky me this last thing had rear its ugly head before we can actually go and start it. Im obviously stuck, i dunno what to buy, i dunno what all works and on top of it all and most importantly im getting very annoyed sinking more and more money into this money pit of a boat. If anyone has a list of part numbers i can use, or links on cheap parts or advice on what to buy or whats better.........please help. Im so close to getting this black cloud out of my life.

The boat was and will only be used in freshwater lakes as well.
 
With a fresh engine, you'd be wise to also replace the exhaust system now.

Look up your year correct OEM exhaust p/n's, and do a search for new exhaust.
You may find that a 2 pc replacement is available.


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Did you identify what happened to the engine that caused the water issue/failure?

If you are 100 % sure it was a engine failure/issue and NOT an exhuast manifold leaking issue then there would be no issue reusing the old manifolds.

The manifolds are cast iron and water getting inside the exhaust passages will leave rust residue.

The maniifolds can be pressure checked to be sure if you have any questions.

The manifolds have nothing to do with your lack of compression but if they have a leak between the water passages and the exhaust passages then water will be drawn back into the motor.
 
Ocso and Barr are good aftermarket parts...stay away from GLM. Check the exhaust shutters to be sure they are present and working.
 
Exhaust shutters are present and appear functional and fine. My engine literally went from running great to.......barely running at all. We hit a nasty wave, and im not sure if we left the water for a split second or whether i was too quick on dialing the throttle back and shutting it down but it appears that the piston rings on 2 and 5 cracked. So im not sure if it had anything to do with my manifolds at all. After this happened, we had taken the boat out a few times to "troubleshoot" and figure out what all was wrong ......but the engine would still run. It would be difficult running on low rpm in the water but once we got rpm's back up it would still hit the speed it always did before.......cause cylinder pressure would build back up. The engine never hydro locked or anything like that but still very strange to me how my piston rings cracked on the 2 pistons.

As for the rust present in the manifolds well they have been off my boat for sometime and fully exposed to the elements. Not sure during my dismantle if water fell into that port or what but im just trying to avoid more headaches than ive already experienced with this thing. I tried posting a pic yesterday but it wouldnt upload.
 
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