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post #1 of 6 Old 08-14-2013 Thread Starter
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Replacing exhaust elbow and plumbing on Universal M12

Hey guys... hope all is well. I'm looking for some advice about plumbing for the exhaust on my Universal M12. I had planned on replacing this stuff last year as it was in obvious need of attention but that slipped down the list as i was working on other things. You know how it goes when working on a tight budget. Anyway... I have located and ordered the replacement exhaust elbow made by Onan. Interestingly, the part number that was cast into the side of the original part has been changed over time and is totally different now. Original number was 170-2834... the new number (for the same size part) is 155-1058. I eventually located it at Coastal Diesel Service in New Bern, NC. Home
So... on to my question: What is the correct type of pipe to use from the exhaust flange to the exhaust elbow? I have read that i should use black iron but that i can also use galvanized steel. The thoughts about using the galvanized steel was that there would be a period of time where it would need to "cure" and that it would give off an odor until it was broken in. Other than that it seemed to be the opinion that galvanized would be fine. What are your thoughts? I've already purchased galvanized because it was readily available but will exchange it if i find any major reasons that i should avoid it. Thanks for taking the time to read... any advice is welcome.

Original piping, elbow...


New galvanized piping... will this be ok?


Old piping and exhaust elbow removed. It was a messy job! I had to disconnect the heat exchanger for clearance and between the spilled coolant and the carbon, it made a huge mess. I do my best to keep things clean but obviously have some cleaning and degreasing to do here...

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post #2 of 6 Old 08-18-2013
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Re: Replacing exhaust elbow and plumbing on Universal M12

Black iron will give you a longer life, but the galvanized is OK. Since you have it, go ahead and use it. When I redid the exhaust on the Universal 5411 (M15) on my previous boat, I found all the black iron I needed at Home Depot.
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post #3 of 6 Old 11-13-2014
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Re: Replacing exhaust elbow and plumbing on Universal M12

This thread of posts has been really helpful to me. Thanks!
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post #4 of 6 Old 11-13-2014
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Re: Replacing exhaust elbow and plumbing on Universal M12

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Originally Posted by Joel73 View Post

New galvanized piping... will this be ok?
Not as good as 'black iron' but should be OK.

I make the recommendations:
1. to 'brace' that heat riser to the engine with a triangular structure (from the top of the riser to the engine) to prevent/lessen the heat riser from vibrating at an independent vibrational frequency than the engine.
2. seal the threads with automotive 'muffler cement' -- partly fit the threads dry, and with the muffler cement applied to the last 'few' in-contact threads, then run the assembly 'home' to seal.
3. Apply heat lagging to the external surfaces to help contain heat in the piping - a woven fiberglass 'tape' with NO binders.

;-)
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post #5 of 6 Old 11-13-2014
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Re: Replacing exhaust elbow and plumbing on Universal M12

Could you post a photo of the triangular brace that you've used?
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post #6 of 6 Old 11-13-2014
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Re: Replacing exhaust elbow and plumbing on Universal M12

If you use the galvi parts,just have really good air ventilation till the zinc burns off. Then lag with glass tape. I seal that with insingglass (a silica hydrate) but that is optional and really old school .Making up two units and keeping one as spare is good as I often weld flanges and don't need to set up twice.Welding apparently is fraught with danger and I agree the last thing you need is a pinhole weld and carbon monoxide .Thats why the thread plugging compound and real good gaskets are important.
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