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Thread: Yanmar Mixing Elbow Corrosion

  1. #1
    Sailing in Alaska Flyertim's Avatar
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    Red face Yanmar Mixing Elbow Corrosion

    Corrosion of the mixing elbow stainless steel close nipple cause a failure of the whole exhaust. While stainless steel offers some resistance to the exhaust corrosion, it is weak mechanically and failed at this point. It was covered in fiberglass insulation and was missed during the survey. The part failed 15 miles out of Anacortes, Wa on my way to Pender Harbor, BC. Has anyone found a better solution to the stock yanmar parts?


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    Tim Anderson
    Sitka, Alaska
    S/V Northern Mist
    Ericson 31 Independence Hull #48

  2. #2
    Moderator Guy Stevens's Avatar
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    Consumable

    Most of the engine manufactures list the exhaust elbow as a consumable. Depending on service there are recommended replacement schedules.

    The other issue is making them out of stainless steel figuring that it is better than other options. A black iron or even a galvanized pipe exhaust system will outlast most of the SS ones out there. You can increase the life span of the SS exhaust elbows by having them electro polished, but that adds significantly to the cost of the unit. The electro polishing eliminates the free iron in the upper surface of the part, leaving chromium and nickle for the surface.

    This is not a good place for SS, SS reacts badly to acidic solutions, which is what is created when the hot exhaust gasses mix with the sea water.

    I would recommend replacement with a black iron unit that you can fabricate out of stock pipe fittings, it will last longer.

    Thanks,
    Guy
    :-)

  3. #3
    Sailing in Alaska Flyertim's Avatar
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    Threaded Close Nipple

    There issue with Yanmar parts is that the aluminum mixing elbow has left hand threads.
    Tim Anderson
    Sitka, Alaska
    S/V Northern Mist
    Ericson 31 Independence Hull #48

  4. #4
    Moderator Guy Stevens's Avatar
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    We are thinking of solving the problem differently

    I would replace the Aluminum mixing elbow in it's entrity with a piece fabricated of of black iron.

    The idea of the mixing elbow in your photo is that it is a cooled jacket which really doesn't make a lot of sense with the fact that the pipe leading to it is not cooled, and will have to be wrapped anyway.

    The cooled jacket type mixing elbows generally result first in a failure on the inside resulting in sea water being injected backwards into the engine damaging the exhaust valves in the last cylinder. A better option in my opnion is to remove the jacketed injection elbow, and replace it with an elbow that you manufacture out of black iron.

    The best of these takes a few hours with some black pipe fittings, a drill and someone with some welding skills to weld the injection port in. However I have seen any number of them fabricated with a bunch of black iron pipe fittings including a T and reducers for the injection port. In my experience these "plumbers nightmares" generally far outlast the shiny stainless steel models. You do have to wrap them up to the injection point in some fiberglass heat resistant materials to keep anything from coming into contact with the hot surface.

    Thanks,
    Guy
    :-)

  5. #5
    Not the newest member Greg Ross's Avatar
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    Guy is right all the way down the line.

    Tim,
    Stainless is subject to a nefarious deterioration due to stress corrosion cracking. Stainless relies on the presence of oxides (oxygen) to maintain it's corrosion resistant properties. There are environments like exhaust systems where that really doesn't work. There are other grades of stainless like Gr 410 that work pretty well in those exposures but not readily available to us.
    Just a reminder, when reinstalling whatever you build do not forget to include a vaccuum breaker in that water injection loop. Pictured below is the way my new-to-me 3HM35F was set-up with that short jumper hose to the water injection nipple. Seller had that hose on there when he shipped me the engine and that's the way the engine and it's new ZF Hurth marine gear and drive saver went into the boat.
    Day after launch I was aboard and went to start the engine, noa-goa. Checked battery voltages since I didn't have the charger hooked up yet. Flicked the de-compression levers and she spun over easy, then started the engine. Logic was she had cooled from the run after launch and ingested seawater. Took the jumper off and replaced it with hose feeds via the existing vented loop, well Duh!
    Actually did this one other time with fresh water home in the yard. After haul-out and extended layups I like to periodically start the engine. I would usually stand a 5 gallon bucket in the Galley and place the raw water intake hose in that Pail. And a hose handy to top it up.
    Got smart one time and figured I could just connect the garden hose directly to the raw water hose and eliminate the intermediate resevoir, not! By the time I was back aboard from turning on the hose, water was spewing out the wet exhaust obviously the pressure was by-passing the flappers in the impellor pump. Water in the engine again.
    Again, spun her on de-compression and then started her right up and then warmed her up, no water in oil, all was good!
    Hopefully I don't live so long that I have to start learning these "Lifes' Lessons" all over again. And if you can't laugh at yourself....... S*** I can't remember!
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    Greg Ross

    LAYLA II
    Independence 31
    Hull No. 63
    Charlottetown, PEI
    Canada


    If you come to a fork in the road, take it.
    ~Yogi Berra


  6. #6
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    Quote Originally Posted by Flyertim View Post
    There issue with Yanmar parts is that the aluminum mixing elbow has left hand threads.

    If you look at the picture in Greg's post, you'll note that in this picture, the mixing elbow is down tight to the manifold. You'd never be able to turn the elbow full circle to screw it down. So, the reverse thread allows for their nut that has threads going in opposite directions so you can draw the two pieces together without actually spinning the elbow in full circles.
    -David
    Independence 31
    Emerald

  7. #7
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    While refitting my boat, I went the iron pipe route wrapped with insulation up to the water injection point. I was able to make it all up with standard parts off the local hardware store shelf. Also increased size from 1 1/2" to 2" to give better flow all the way thru the water lift muffler, exhaust hose and thru hull. This is on a Universal 5432.

    The boat was not in the water or running when I got it so I have no comparison on performance.

    Seems to work fine. I know my Prop is a bit to large for the engine, but I can cruise at 6 knots (1800rpm) and make 7.2 knots at full throttle(2300 rpm). Have 4 months and about 30 hours on the engine.

    Planning to change prop soon



    Regards
    Greg Dettmer
    e38- s/v Spirit Soul

  8. #8
    Principal Partner CoryBolton's Avatar
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    Threading Adapter

    Quote Originally Posted by Flyertim View Post
    There issue with Yanmar parts is that the aluminum mixing elbow has left hand threads.
    We had one of those Yanmar exhaust elbows (on our Universal 5424) that bit the bullet this last summer. While replacing it with something "better" is probably a good idea, we took the path of least resistance and replaced it with nearly identical parts.

    As to the left/right threading issue you noticed, we were able to buy an off-the-shelf threading adapter from the same place we bought the replacement elbow for about $20.
    Last edited by CoryBolton; 11-20-2011 at 06:23 PM.
    Cory
    1984 E-35III #163 "Balancing Act"
    Portland, OR

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