Exhaust elbow metallurgy ... help!

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Albert Ross

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Being fed up with the carp quality of Yanmar 3YM30 exhaust mixing elbows, I've been asking the excellent people at ASAP if they could supply the required components to make one up, rather than buy a new ready made one from Yanmar.....
anyway ASAP have suggested the following:

1. A mild steel exhaust flange that bolts on to the engine
.... leading to
2. A brass 45 degree elbow that screws into the exhaust flange
.. and leads to
3. A stainless steel (316) exhaust outlet spray head
.. leading to the 2 inch exhaust hose that goes via the muffler / water trap to the outside.

My questions:
Will these different metals get on together OK?
Will the exhaust gases melt the brass elbow?
Will 316 s/s last OK with hot exhaust mixing with the cold seawater in it?

Thank you.
 
First question has to be 'why do you find the existing manifold to be poor? My 3GM30F manifold is well over ten years old, engine has done about 2200 hours, original manifold, no corrosion and no problems. It is all 300 series stainless.

Answering yours, definitely not a happy mix of metals. Look on Ebay for people making copies in stainless steel for considerably less than Yanmar sell them for.
 
My concern about the quality stems from the very early failure of mine and a number of comments from other forumites here and elswhere.

With regard to the mixture of metals, thank you for your expert advice.
 
flat1 said:
My concern about the quality stems from the very early failure of mine and a number of comments from other forumites here and elswhere.

With regard to the mixture of metals, thank you for your expert advice.
Click to expand...

Try these guys http://www.dam-marine.com in France, I bought a stainless steel elbow from them for my GM10. That have bought a lot off stock from an American manufacturer, maybe they can help you.
For what it's worth I found them to be excellent communicators, and prompt service. Total cost inc p&p was cheaper than Yanmar part, about €190 vs £190, or thereabouts.
 
Hot salt water is very corrosive even on stainless steel.
I had a hole corrode through a fabricated stainless exhaust elbow on a couple of occasions.
The culprit seemed to be the welded parts.
Maybe Vyv can come back with some metallurgy for us.
 
I have a high level mixer on my 1GM10. There is a 90 degree cast (iron?) elbow, a simple brass male to male fitting curtesy of Plumbbase, and a cast bronze 180 degree bend with the salt water channel cast inside. The brass/cast iron interface lasts around 10 years (I had to replace both last season) but at no time does the raw water find it's way back into the exhaust manifold from this set-up.

The 1GM10 mixer elbow is mild steel. The salt water channel is known to corrode allowing the coolant to flow back into the manifold with potentially and predictably disastrous effects on the cylinder head. A sailing Pal has has his head welded by a specialist and machined back for a fraction of the cost of a new head after such a failure. I'd find it strange if Yanmar supplied a SS fixture with there bigger engines but not the 1GM10, but I'm no expert in the marque.

The mixture of metals proposed in the original post contains materials with three different electrovalent properties in close proximity. My take would be the interfaces between the brass and both SS and Mild steel would be vulnerable.

I reckon the whole thing would be better in marine grade SS.
 
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SHUG said:
Hot salt water is very corrosive even on stainless steel.
I had a hole corrode through a fabricated stainless exhaust elbow on a couple of occasions.
The culprit seemed to be the welded parts.
Maybe Vyv can come back with some metallurgy for us.
Click to expand...

The classic problem is known as sensitisation. If either the parent metal or the filler rod has a significant carbon content some of the chromium around the weld combines to form chromium carbides, leaving the HAZ low in chromium. It is then vulnerable to corrosion. Welded parts should be made from 304L or 316L, where the L stands for low carbon. There are also more fancy alloys containing niobium or titanium, both preferential carbide formers so the chromium remains as it should be.

The failure is sometimes known as 'knife line attack' because it occurs along a very narrow line adjacent to the weld, that looks as if it has been cut by a knife.
 
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That time of night again, but apart from it's extreme ductility which could affect mounting bolts torque etc, wouldn't a lead exhaust manifold, or a lead/ antimony alloy as used in batteries be extremely corrosion resistant ? Very easy to cast due to the low melting point.

Titanium would be ideal I suppose, but that's a different ball game altogether.
 
rubbishman said:
I don't think I have the expertise of Vyv but I'm wondering if 904 would be a good choice.
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The maximum service temperature is only 450°C so not much use for an exhaust manifold. Main uses are for condenser tubes, heat exchanger tubes and control and instrumentation tubes
 
GrahamHR said:
That time of night again, but apart from it's extreme ductility which could affect mounting bolts torque etc, wouldn't a lead exhaust manifold, or a lead/ antimony alloy as used in batteries be extremely corrosion resistant ? Very easy to cast due to the low melting point.
Click to expand...
Not much good in a HOT exhaust manifold where the temperature of the gasses can easily exceed the melting point of lead/lead alloys
 
GrahamHR said:
That time of night again, but apart from it's extreme ductility which could affect mounting bolts torque etc, wouldn't a lead exhaust manifold, or a lead/ antimony alloy as used in batteries be extremely corrosion resistant ? Very easy to cast due to the low melting point.
Click to expand...

I remember that when I still retained the optimism of youth I soldered the exhaust pipe of my car. It lasted about five minutes.

Several engine converters, Beta and Nanni I think, are supplying aluminium exhaust manifolds. I found this a little surprising but they seem to last OK. Aluminium is relatively easy to cast and might make an interesting project to anyone interested. Years ago I met a man who made very nice laminated canoe paddles. He needed dozens of G-cramps and cast his own in aluminium.
 
Robin said:
Got me worried enough to look at prices, found this http://exhaustelbow.com/ shipping worldwide included, I'm tempted to buy one as an on board spare which would gaurantee it never to be needed. Our engine has 1258 hours on from new and still has the original elbow which still seems OK
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That's a good price, assuming carriage to Europe does not cost too much. I recently bought a spare in Greece, cost me €190, which was less than the UK price, mostly over £200. As it turned out the water leak that prompted the purchase turned out to be from the hose, so the replacement manifold was not needed. My 3GM30F has done 2200 hours and the original manifold is in as-new condition.
 
I've been following this thread and I realize how lucky I am to be able to weld.I'd Tig weld an elbow like this in a couple of hours .
 
vyv_cox said:
That's a good price, assuming carriage to Europe does not cost too much. I recently bought a spare in Greece, cost me €190, which was less than the UK price, mostly over £200. As it turned out the water leak that prompted the purchase turned out to be from the hose, so the replacement manifold was not needed. My 3GM30F has done 2200 hours and the original manifold is in as-new condition.
Click to expand...

According to their website the price includes shipping to anywhere in the world, there are lower prices too for buying more than one unit.

The Yanmar 4JHE we had on our Sun Legende back in UK had 4,400 hrs on it when we sold it at 20 years old and the elbow on that was the original too. Previously engines on boats owned over the years with various Bukh and Volvo motors and one Mercedes, we did have to replace elbows at least once.
 
I watched this with interest in the hope that someone would bring up a Volvo exhaust manifold replacement in Stainless ,
but the Exhaust Elbow guys only make manifolds for Yanmar .

are there any made for the smaller Volvo Penta engines ?
 
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