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Old 06-08-2012, 17:56   #16
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

I build light aircraft that use a Solo 210 two stroke and the factory exhaust always brakes at the weld ..I fixed the problem by putting a flexable ball and socket joint where the weld is ...mine fall apart because of vibration not heat..they also come from the factory like yours ,hard metal to metal,this is not a good thing..if you look at a dirt bike ( honda,yamaha) they dont put hard metal to metal,they use a socket and ball joint in the pipe...this might work for your engine as they vibrate quite a lot... good luck..I also tried early on to weld a piece of pipe on the inside of the factory pipe but it broke too...ball joint and springs works great..DVC
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Old 06-08-2012, 19:09   #17
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

After great thought i decided only a fool would do what I just suggested!...... Im slow but,I come around eventually..DVC
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Old 07-08-2012, 02:25   #18
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

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Originally Posted by DotDun View Post
Are just the welds failing? Take 'em to a welding shop, they can fix 'em.
Have already tried with marginal success.

Often it never "seals" correctly, and if it does, it only lasts a short additional amount of time.
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Old 07-08-2012, 04:33   #19
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

I just got through having the same issues yet again with both of my 2GM20F. The steel Yanmar uses is soft and the flange usually warps and will leak salt right on your fuel pump. A real pain to be sure.
I found a really nice and helpful guy that fabricates these out of SS for the 2GM20F at $150 each, plus free shipping within the States. I'm very happy with the way they are made. I just installed them and they work and look great. I can't speak on their longevity as I just installed them but I'm betting they'll last a lot longer than the Yanmars. If you want his number just shoot me a PM I'm sure he'll be happy to answer any questions you may have.
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Old 07-08-2012, 04:56   #20
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Had mine go on my 2 4jh4e yanmars after 500-600 hours.
Got a friend who is a gun welder to weld them up properly and 1200 hours later not a drip.
The factory join is too light on.
Worked out much better than the $500 replacement offer.
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Old 07-08-2012, 17:42   #21
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

If you are looking for a different material. I pieced together an elbow on my GM2F with 1 1/2" npt black steel pipe. $30.00 for the pipe and after 2yrs still fine. Do not use galvanized pipe. Produces toxic fumes when hot.
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Old 08-08-2012, 02:09   #22
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

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If you are looking for a different material. I pieced together an elbow on my GM2F with 1 1/2" npt black steel pipe. $30.00 for the pipe and after 2yrs still fine. Do not use galvanized pipe. Produces toxic fumes when hot.
Any photos would be great if you have time to post some. Would be interested to see what you did.
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Old 08-08-2012, 18:34   #23
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

I'll take some pictures next time I'm at the boat.
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Old 15-02-2017, 14:30   #24
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

Forget buying the OEM parts as for about the same money it is possible to buy aftermarket exhaust parts in stainless steel. Incidentally I don't really like Yanmar engines as IMHO some of the engineering techniques are exceedingly poor. One example is the grey cast iron (strong in compression but weak in extension) crankshaft pulley which is mounted on a taper. These pulleys are apt to fracture through the key-way. The British company Villiers did better than that with their industrial engines as with these the cast iron pulley had a steel boss.

Constant erosion of the mild steel elbow suggests that the thermostat may be to blame as hot seawater is probably a lot more corrosive than warm seawater.
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Old 15-02-2017, 15:43   #25
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

The U shaped 2/3GM series elbows are good for about 7 years then they corrode out.

Personally I wouldn't want one made of stainless steel. Hot exhaust gases plus salt water are very hard on the welds and it's not unusual to see lots of pinhole failures in those areas.
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Old 15-02-2017, 18:29   #26
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

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Originally Posted by boatbod View Post
The U shaped 2/3GM series elbows are good for about 7 years then they corrode out.

Personally I wouldn't want one made of stainless steel. Hot exhaust gases plus salt water are very hard on the welds and it's not unusual to see lots of pinhole failures in those areas.
I just replaced 2 original exhaust manifolds (1980 boat) that were leaking salt water from the bosses holding the freeze plugs. They were rotted out badly.After pricing OEM manifolds at $4,000.00 for 2, I took a chance and ordered 2 stainless manifolds from a company in Alabama for $1,200. each. Takes them a week to fabricate. When they arrived I was so impressed with the quality I hated to install them. I would have happily displayed them on the coffee table as works of art. I finished installing the 2nd one 2 weeks ago and the boat is operational again. To soon to know but I expect them to outlast me. Also have stainless mixing elbows and I mounted the elbows with stainless header studs and nuts with lots of C5-A never seize.
I'll post if any thing unusual occurs or problems (defects)
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Old 15-02-2017, 21:39   #27
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

The exhaust elbow on my 2QM15 ( raw water cooled) rusted out at the weld also. After checking into alternatives, and suffering sticker shock at the prices, I decided to do some investigating.

On the 2QM15 the flange that comes off of the exhaust manifold is held to the manifold by four bolts and is threaded dead center where the exhaust elbow screws in. I removed the flange and using heat & big wrench managed to separate the flange & elbow. Sand blasted and painted the flange with multiple coats of high heat paint.

Went to my local wholesale plumbing outlet and bought 1-1/2 inch threaded nipples and couplings in heavy wall 304 Stainless Steel.

The order I assembled them starting at the exhaust flange was: 2" long nipple- 45 degree elbow- 6" long nipple- which then connected to the hose to the muffler. I dry fit and marked for alignment with a paint pen. Then took the 45 degree elbow to my local welding shop and had them drill a hole and weld a 1/2" SS threaded coupling where the cooling water hose would connect. Threaded in a SS 1/2" male thread x 1/2" hose barb to connect the water hose to.

Assembled the whole thing with Permatex exhaust gasket goop at each thread and bolted it on. Worked like a charm and the whole thing cost me about $50 (and thats CDN dollars!) Took it off for inspection at the end of the season and it looked great, and at that price I could build a new one every year.

I dont know if the 2GM20 has the same arrangement coming off the manifold (couldnt find a good pic of it) but even if you had to have the piece threaded, it might be worth it.
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Old 15-02-2017, 21:50   #28
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

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Originally Posted by kiltym View Post
Here are some photos of the installations, in case anything looks "odd" to anyone.
While I realise this thread was started nearly 5 years ago and the OP has apparently sold the boat, but I agree with tropicalescape (post #16) that this is not a heat related issue, the repeatedly occurring failures of the welded seam are caused by vibration. Probably amplified by the poor quality of the Yanmar's elbow, these ones are very thin also is that correct, certainly not sturdy enough.
2GM20F is a twin cylinder engine thus vibrating much much more than a smoother running four cylinder engine. The elbow is located pretty much near the TOP of the engine, connected to the exhaust hose, connected to the wet muffler which is fixed solid to the hull. As the engine is running (and vibrating) the hose is constantly exerting stress on the elbow and "trying to shake it off" and the weakest link (welds) will eventually fail. You could say the Yanmar elbow was not engineered with enough margin against vibration.

If that had been my boat and had the issue of going through elbows at a rate of one per 50 hours I would have tried the following:
1) replace the exhaust hose if the old one has hardened and is not flexible anymore
2) make sure the hose is nicely aligned at the wet muffler end so not to cause any twisting force to the elbow when the engine is running (on the photo it looks like the hose is connected to the wet muffler at an angle which maybe a problem, pulling the elbow to one side) and so that the hose has enough length to accommodate the vibrations (so a vibration cycle does not pull out all the slack off of the hose causing a high force to be exerted on the elbow)
3) check the condition and the alignment of the engine mounts, if any doubts replace and let a pro do the alignment (if one is not confident enough to accomplish as diy)
4) if the elbows still keep failing get a SS elbow. But I would isolate the SS elbow from the connecting aluminium using a high temp exhaust sealant or similar as there is a chance the non-matching metals will cause corrosion to the exhaust manifold which is aluminium on the Yanmar is that correct? I reckon this is the reason most OEM elbows are aluminium, matching the metal they attach to and so minimising corrosion. At least I would keep a close eye on it. An aluminium elbow is cheaper to replace than a corroded manifold.
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Old 15-02-2017, 22:05   #29
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

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Originally Posted by ErikFinn View Post
If that had been my boat and had the issue of going through elbows at a rate of one per 50 hours I would have tried the following:
1) replace the exhaust hose if the old one has hardened and is not flexible anymore
2) make sure the hose is nicely aligned at the wet muffler end so not to cause any twisting force to the elbow when the engine is running (on the photo it looks like the hose is connected to the wet muffler at an angle which maybe a problem, pulling the elbow to one side) and so that the hose has enough length to accommodate the vibrations (so a vibration cycle does not pull out all the slack off of the hose causing a high force to be exerted on the elbow)
3) check the condition and the alignment of the engine mounts, if any doubts replace and let a pro do the alignment (if one is not confident enough to accomplish as diy)
4) if the elbows still keep failing get a SS elbow. But I would isolate the SS elbow from the connecting aluminium using a high temp exhaust sealant or similar as there is a chance the non-matching metals will cause corrosion to the exhaust manifold which is aluminium on the Yanmar is that correct? I reckon this is the reason most OEM elbows are aluminium, matching the metal they attach to and so minimising corrosion. At least I would keep a close eye on it. An aluminium elbow is cheaper to replace than a corroded manifold.
1. Exhaust hoses were all replaced when we purchased the boat. We used very flexible hose, not the stiff kind.

2. The port engine hose had a slight pull as shown in the photo. The stbd engine was straight, which can be seen in the other photos. Both engines had the same continuous issues with the elbows. There was a lot of flex in the hose so I doubt this was really the issue.

3. All engine mounts (3) were replaced when we bought the boat.

4. This is what we did. We used the standard Yanmar gasket between the elbow and the manifold as it is a thick heavy duty material that provides isolation between the aluminum and SS. Issue solved. The Yanmar "standard" elbows are very weak. They make a forged version which is likely fine, but had no vertical room to accommodate it so we had to use the more standard, low profile, versions.
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Old 16-02-2017, 00:02   #30
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Re: Yanmar 2GM20F Exhaust Mixer/Elbow

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Originally Posted by kiltym View Post
No zincs on 2GM20F. Only on the saildrives.

The insides of them are clean (since I have to change them every year ). Only when I first bought the boat was there a little buildup inside the elbows, but now they are basically clean, and I remove and check once per year if the elbow was not replaced.

They leak at the weld shown in the photo, and the one time that got real bad, also at the weld on the surface of the mounting flange which caused the heat exchanged to rot out. Since then, I don't let them get bad, and replace once I see a small amount of weeping occur.
This is incorrect, they do have zinc on the block above and forward of the lift pump . They are Into the water/antifreeze jacket so they rarely fail. Verified this on a new old stock crate 2gm20f and a older replaced 2gm20f.
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