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Old 12-02-2006
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Exhaust mixing elbow

A friend has a Westerbeke 4kw genset in need of a new exhaust mixing elbow. The existing one has some carbon buildup and a small leak.

The existing one is homemade with a 0.75 in pipe nipple (for the water) welded into a 1.5in pipe nipple (for the exhaust). I thought it would be ok to fab up a new one like the old one, but another friend adamantly insisted that the homemade unit would damage the engine. He went on at great length about the possibility of drawing water into the cylinder thru the exhaust valve on the engine because the exhaust valve is not closed when the pistons begin their intake stroke. I'm not a diesel mechanic, but I wouldn't expect the intake and exhaust valves to overlap enough for this to be a real problem. I thought large overlaps were for high rpm racing engines, not for diesels. Anyone got an opinion? Let me rephrase--anyone got an opinion based on experience? :-)

Since the old homemade unit worked for over 20 years, I am inclined to endorse a homemade over the cost of a factory replacement.


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Old 12-02-2006
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I have a Westerbeke propulsion engine that had just such a riser until last year. It lasted 35 years (with a little welding - note it was bronze fittings) with no problems. It was replaced as part of an entire replacement of the exhaust system - the aqualift muffler had rotted away.
I would be comfortable with a handmade replica of the original. Just don't get creative, the design might have some subtleties.
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Old 12-02-2006
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There is no problem fabricating your own mixing elbow - especially when you see what the manufacturer charges for an "original".

Follow the original in concept (line sizes, shape, height and orientation) and you'll do fine. We built one out of stainless steel pipe fittings (threaded), welded in the water connection and back welded the threads - still going strong 10 years later.

Be sure to use the proper high temperature gasket material on the exhaust manifold if it's flanged.

Water getting back into the engine has more to do with your practices (or exhaust system layout) than the design of the mixer elbow. Always close the raw water intake if you are needing to crank the engine for extended periods without running (eg when bleeding the fuel system or otherwise having difficulty starting)
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