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Exhaust Elbow Replace or Suck it up?


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Ran the engine- a Volvo D2-40 and got the overheat alarm so ended up daisychaining up the system,  water pump good, heat exchanger slightly blocked now removed and cleaned but when I checked the exhaust elbow too it was half blocked with cruddy calsified carbon.

Soaked it overnight in acetone but appears to have done sweet FA

Ovlov want moonbeams for a replacement ($ 767.00) surprising no one here,  but I'm thinking the elbow is really a flawed design and I'll be faced with another elbow a few years down the track.

As most of you know the heat exchanger raw salt water enters the exhaust via an external jacket and swirls with the gases, there is a significant build up of crud for about 40mm below the water entry point but interestingly there is build up 40mm above (Uphill) the water entry point also which only leaves an 85mm horizontal run to the engine manifold

I'm thinking I may replace with a fabbed stainless with the heat exchanger water entering just a little further down, anyone done this?

I'm looking for feedback.

 

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Ive got an SS elbow on my 2GM, its basically an inverted U with a hose nipple welded to it. Last year I removed it to clean any crud and it was pretty much perfect. I believe its because I run it 80-90% most of the time (its only 13hp) so it gets hot and doesnt get a chance to build up. I would have zero hesitation getting a replacement fabricated in SS, you might even be able to buy the bends. Handy hint do not go to a marine place to get it made if you want to save $$, try a rural engineering place that does milking plant repairs. 

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I have made some nice ones over the years myself... I suggest 10G pipe instead of tube. Fabricated SS can be fine but be wary of the grade, some are prone to chloride stress corrosion and the acids formed from the sulfur in the fuel.

Hot dip galvanized mild steel has been used successfully.

But at the end of the day... 6 to 8 hours labour... depending on the build quality at .. what $80 per hour (What is the current labour rate now days?) is $500 minimum plus materials, wait times, adjustments when it does not fit perfectly travelling etc..... I do not think there is much to be gained not buying the OEM unit as un-pleasant as that experience may be. unless you can get good "Mates Rates"

 

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26 minutes ago, Psyche said:

Ive got an SS elbow on my 2GM, its basically an inverted U with a hose nipple welded to it. Last year I removed it to clean any crud and it was pretty much perfect. I believe its because I run it 80-90% most of the time (its only 13hp) so it gets hot and doesnt get a chance to build up. I would have zero hesitation getting a replacement fabricated in SS, you might even be able to buy the bends. Handy hint do not go to a marine place to get it made if you want to save $$, try a rural engineering place that does milking plant repairs. 

I have a guy...

 

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You could get an aftermarket stainless one.   Just search for d2-40 stainless exhaust mixer.  Here is one. 

https://www.marineenergy.com.au/products/volvo-penta-v878-stainless-steel-mixing-elbow-replacement

I had a custom riser made. But it cracked after an estimated 150 heat/cool cycles which was pretty disappointing.  I had it repaired, but obviously the stainless is weakened so it gives me some cause for concern.

I have heard that the cast one's corrode and the stainless cracks. 

I have kind of reached the conclusion that these things are disposable items.

Also check for corrosion at the heat exchanger exhaust outlet. This is the D2 (and d1) Achilles' heel.   This photo is from a D1-30 but same problem.

If you are seeing corrosion here, then water is getting back up the exhaust mixer and you would benefit from a riser. 

image.png.91ebdd3fd0e7e97244d5c22644d60050.png

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In the food and dairy industries for cold water 304 & 316 stainless is used, up to 55 deg C 316 stainless and over 55 deg C 2205 stainless is used.

Bit of reading for you.

Stainless Steel Stress corrosion information.pdf Wet Corrosion - Stree corrosion cracking.pdf Atlas steel - Stress corrosion and pitting corrosion information.pdf Stainless Grades Corrosion - Atlas Tech handbook.pdf Stainless Grades Corrosion - Corus Tech-Info[1].pdf

its amazing what is buried deep in the hard drive.

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Good to know, building one economically is really dependent on the complexity of the riser and who you know. Regarding going to a non-marine fabricator I was fortunate enough to meet somebody in the dairy industry who was very knowledgeable about stainless, but any good metal worker with a pulse tig and pipe bending gear will do!

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Thanks Sloop and everyone else for your well considered replies. I am leaning toward a stainless replacement, will get some quotes together and see where to from here.

MCP that website is a good find a stainless elbow at £225 works out to NZD 430 plus the shipping and handling will look into that furher.

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2 hours ago, harrytom said:

Why  ss ?? Steel last just as long.Easy to fabricate . My original lasted 30 yrs and only reason of failure was due to rusting under instillation.Didnt go from inside out.

 I have successfully made mild steel flanges and elbows then welded on a simple straight SS mixer and water injection fitting at the end.

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I'm running a mild steel one, (kubota D1105) 10 years so far, SS has plusses and minus's one is that it work hardens and with heat changes this is accelerated. Lack of oxygen is also an accelerator. Schedule 40 Mild steel minimum thickness. Thicker schedule 80 probably overkill.

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On my MD7 i purchased cast SS plumbing fittings from anzor in east tamaki, screwed them together and had a fab shop do the welding, I recycled the Plain steel four bolt flange by welding it to the SS fittings. If you do the fabrication and jig it up the welding time per see is minimal I think mine cost $100. vs OEM part @$800

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I did a similar thing around 7 years ago.  Cost around a hundy.  Just about time for replacement 

2 hours ago, Frank said:

On my MD7 i purchased cast SS plumbing fittings from anzor in east tamaki, screwed them together and had a fab shop do the welding, I recycled the Plain steel four bolt flange by welding it to the SS fittings. If you do the fabrication and jig it up the welding time per see is minimal I think mine cost $100. vs OEM part @$800

 

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As said by a couple of people above, I've recently bought a stainless one for my yanmar from hdi marine. Haven't fitted yet, but looks better and much cheaper including shipping than oem from the local agent and was here in a week.

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