Yanmar 4JH4 1000 hour service

[jviss]

You have apparently made up your mind and decided to use the old mixing elbow.

It's only four years old!

I think it one wanted to throughly inspect one, you would remove it and hold it and strike it with something so that you could hear it "ring." That might tell you a lot about the condition. But I think with a 4 year old elbow, and 1,000 hours, the kind of hours the owner describes, a visual inspection would suffice.

 

[CarlN]

Charles, are you saying that the corrosion would not be visible on either the inside or outside? The metal is only 1/8" thick. How would corrosion get started except from a surface? Even galvanic corrosion would show color change. Stress fractures will show and most likely drip long before it fails. There's no flexing so fatigue isn't a concern.

I've never heard of replacing an exhaust elbow that didn't have obvious visible problems - usually inside.

In any case, I do plan to look inside. This elbow is already at 1000 hours when Yanmar said it had to be replaced at 500 hours. Maybe I just got lucky. Or maybe the manual is too conservative.

 

[SG]

Do you have bronze mixing elbow, Carl?

 

[jviss]

So, I see you're in Bristol, RI, Carl. No good Yanmar mechanic nearby? That's disheartening. I will ask my surveyor, who seems to know everyone, and works primarily in the RI area.

 

[Charles Erwin]

Carl - the 500 hours is clearly a safe number - just like helicopter parts that get replaced at a safe number no matter they might be just fine.

Take a look at how the mixing (elbow) section is made. There is an internal tube (exhaust passage) and an external tube. The water inlet is injected through the external tube and and exits a ways down stream at the end of the internal tube then overboard. That way water cannot find its way into the turbo exhaust drive fan nor the head and the water cools the exhaust filed internal tube as well. The problem is the internal tube welds decay and when that happens water can get into the inner exhaust tube and so the turbo drive fan and the exhaust valves can possibly become exposed to water.

The inspection issue is that you can't see the welds because they are way up inside the assembly - between the internal and external section walls. Even if you could see up there you can't measure how much decay is present or predict when it will give way. The bottom line is that if a failure occurs in use (and it will eventually) there will be no symptoms until salt water damage is well underway.

Charles

 

[CarlN]

Charles,

I learn something new everyday. Thanks. Hadn't focused on the welds as the failure risk.

Still not sure I want a "new to me" mechanic to fool with it (in Oriental now) but I'll have my Florida guy look at it when I'm there in a few months.

 

[CarlN]

After investigating a bit more the mystery may be that Yanmar has used two different exhaust elbows on this engine. While I can't confirm as I'm not at the boat, I believe mine is the newer "improved" design. I will still have it checked but this switch would present a challenge to the Yanmar manual writers.

 

[Charles Erwin]

That is for non turbo version Sent you PM with possibly better source and attractive price.

 

[CarlN]

To report back. I finally got to my preferred mechanic for the 1000 hour check. One valve needed adjustment (a bit tight). Exhaust elbow was checked and is fine (it is the Yanmar optional one that rarely needs to be replaced. This is still the original). Did a turbo wash. Of course oil/filter/transmission fluid all changed. Everything else fine. Love these engines.