Replacing exhaust mixing elbow on Yanmar QM-15 (1980 Hunter 33). Do I need Yanmar OEM equipment? Is there a recommended substitute?
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It is pretty cheap!
You could have a machine shop make up a substitute, which we often have to do, here in Mexico. But, the Yanmar part is not expensive, and I would suggest you stick with it. The complication will come when you try to remove the elbow, since there is not enough room to spin it off. Instead, remove the fitting it goes into, and then remove the elbow from that fitting. There is a cork and copper gasket in there, and there is a technique for reusing it, but do yourself a favor and get a new gasket, as well. I assume your engine has been overheating, in which case this will probably help. I change my elbow about once every four years. Good luck.
You could have a machine shop make up a substitute, which we often have to do, here in Mexico. But, the Yanmar part is not expensive, and I would suggest you stick with it. The complication will come when you try to remove the elbow, since there is not enough room to spin it off. Instead, remove the fitting it goes into, and then remove the elbow from that fitting. There is a cork and copper gasket in there, and there is a technique for reusing it, but do yourself a favor and get a new gasket, as well. I assume your engine has been overheating, in which case this will probably help. I change my elbow about once every four years. Good luck.
Elbow Coupling
The coupling between the elbow and the manifold is stainless and has both left and right-hand threads for ease of removal. The problem is if it was tightened too tight the threads will gall up when you try to take it apart. When you get the new elbow that's a good oportunity to ask the parts people about any recommended technique for assembly.
The coupling between the elbow and the manifold is stainless and has both left and right-hand threads for ease of removal. The problem is if it was tightened too tight the threads will gall up when you try to take it apart. When you get the new elbow that's a good oportunity to ask the parts people about any recommended technique for assembly.
are you sure John?
John: Are you sure that this is stainless? When I did mine, it was awfully rusty to be stainless steel. The one thing that I remember is that the manifold has a thread that goes one way and the elbow has the opposite thread. When I re-assembled mine, I used a never-sieze compound. I have not tried to take it apart again to see if it helped or not. The one thing I will recommend is that you have a torch and a large vice to get the pieces apart.
John: Are you sure that this is stainless? When I did mine, it was awfully rusty to be stainless steel. The one thing that I remember is that the manifold has a thread that goes one way and the elbow has the opposite thread. When I re-assembled mine, I used a never-sieze compound. I have not tried to take it apart again to see if it helped or not. The one thing I will recommend is that you have a torch and a large vice to get the pieces apart.
Archives
Check the Archives and type in the words "mixing elbow" for a complete discussion of all points.
Check the Archives and type in the words "mixing elbow" for a complete discussion of all points.
Left vs. right?
It's been a few years but I do not remember any left-handed threading. Four years ago while reading about all the problems with the elbow I decided to remove and check mine. It's a 1979 2QM20 and I am pretty sure it was just two right-hand bolts at the manifold and a clamp for the exhaust hose on the other end. It came right off and was clean as a whistle. This makes me think the previous owner either cleaned or replaced it. Probably replaced since it was solid with no sign of thin spots or corrosion. This has been a freshwater only boat. Does that make a difference?
It's been a few years but I do not remember any left-handed threading. Four years ago while reading about all the problems with the elbow I decided to remove and check mine. It's a 1979 2QM20 and I am pretty sure it was just two right-hand bolts at the manifold and a clamp for the exhaust hose on the other end. It came right off and was clean as a whistle. This makes me think the previous owner either cleaned or replaced it. Probably replaced since it was solid with no sign of thin spots or corrosion. This has been a freshwater only boat. Does that make a difference?
Right, Left, Right.....
Ed: The threads I was talking about is the coupling between the Elbow and the Manifold on the GM engine.
Ed: The threads I was talking about is the coupling between the Elbow and the Manifold on the GM engine.
Mixing Elbow
Bought my replacement from Mack Boring in NC but I think Mastry Engine Center in St Pete would be your best bet. Instead of breaking out the blow torch and bench vise, I just unbolted the whole assembly from the engine and took it to a muffler shop where the guy charged me $10 bucks to remove the old part and install the new then I reinstalled it on the engine. Don't forget to order the gasket also. The link below is for Mastry Engine Center. http://www.mastry.com/
Bought my replacement from Mack Boring in NC but I think Mastry Engine Center in St Pete would be your best bet. Instead of breaking out the blow torch and bench vise, I just unbolted the whole assembly from the engine and took it to a muffler shop where the guy charged me $10 bucks to remove the old part and install the new then I reinstalled it on the engine. Don't forget to order the gasket also. The link below is for Mastry Engine Center. http://www.mastry.com/
Andy's experience the same as mine.....
...as I mentioned in my ORIGINAL reply, take off the piece the elbow goes into, and then remove the elbow. The QM, as opposed to the GM, does not have left hand/right hand threads, nor is the original stainless. And, it is the bulkhead, not the engine, that resists unscrewing the elbow in place. The original part not being stainless is a good thing, by the way, since stainless is not very resistant to the sulphuric acid formed by salt water and exhaust gasses, which is why everyone will by now have replaced their stainless waterlift mufflers with plastic or fiberglass....but that is another story!
...as I mentioned in my ORIGINAL reply, take off the piece the elbow goes into, and then remove the elbow. The QM, as opposed to the GM, does not have left hand/right hand threads, nor is the original stainless. And, it is the bulkhead, not the engine, that resists unscrewing the elbow in place. The original part not being stainless is a good thing, by the way, since stainless is not very resistant to the sulphuric acid formed by salt water and exhaust gasses, which is why everyone will by now have replaced their stainless waterlift mufflers with plastic or fiberglass....but that is another story!
QM vs GM
Didn't realize there was a difference between the QM and the GM. My experience is with GM30(F) which is apparently different. The coupling on the GM30(F) has both left and right-hand threads which allow the elbow to be removed just by unscrewing the coupling. The couplings that Doc Freeman in Seattle sells (they are a Yanmar dealer) are stainless. With regard to use of an anti-seize compound Doc's says not to use one that has copper in it like Never Seze because it will gall even worse. They also said not to tighten the threads too tight as this will cause galling also. I used an anti-seize compound but I don't remember what it was. And for what it's worth, I'm on my third mixing elbow (the original being the 1st) in 13 years. Also, my bulkhead does not allow for unscrewing the coupling, either!
Didn't realize there was a difference between the QM and the GM. My experience is with GM30(F) which is apparently different. The coupling on the GM30(F) has both left and right-hand threads which allow the elbow to be removed just by unscrewing the coupling. The couplings that Doc Freeman in Seattle sells (they are a Yanmar dealer) are stainless. With regard to use of an anti-seize compound Doc's says not to use one that has copper in it like Never Seze because it will gall even worse. They also said not to tighten the threads too tight as this will cause galling also. I used an anti-seize compound but I don't remember what it was. And for what it's worth, I'm on my third mixing elbow (the original being the 1st) in 13 years. Also, my bulkhead does not allow for unscrewing the coupling, either!
OEM was not Stainless!
John: The OEM connector was not stainless on our 2GM20F. I belive that fresh water does not creat the build up of coke in the mixing elbow like it does in saltwater. I suppose that there is a chemical reaction between the saltwater and diesel exhaust that causes the build up. I replaced mine after 11 years and there was some carbon but nothing excessive. Ed Schenck also experienced the same. I also never cruise with the engine below about 2500 rpms either.
John: The OEM connector was not stainless on our 2GM20F. I belive that fresh water does not creat the build up of coke in the mixing elbow like it does in saltwater. I suppose that there is a chemical reaction between the saltwater and diesel exhaust that causes the build up. I replaced mine after 11 years and there was some carbon but nothing excessive. Ed Schenck also experienced the same. I also never cruise with the engine below about 2500 rpms either.
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