follow up on exhast elbow

Isn't there a misunderstanding about how these elbows work? Normally, the inner pipe is spaced-off of the outer pipe so that some of the gas goes outside the inner pipe and mixes with the water. The way this new design seems to be arranged is for all the gasses to by-pass the water inlet until almost to the end of the elbow. This is a MIXING elbow. The water isn't to cool the inner pipe; the point about a wet exhaust is that the gasses are cooled and contract in volume, so can be handled and exhausted through rubber pipe, quietly. Where, in this new design, does the gas mix with the water? As I said earlier, I am not a diesel mechanic ---- that's what we need because I think that there is something not quite right about this.
 
Admire your ingenuity, but seems to me a bit overkill when a replacement to the original is so readily available. I know they have a reputation (probably undeserved) for short life, but this is usually the result of a poor installation, particularly failing to have an anti syphon valve and a water trap in the system. Mine is still fine after more than 20 years!
 
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Admire your ingenuity, but seems to me a bit overkill when a replacement to the original is so readily available. I know they have a reputation (probably undeserved) for short life, but this is usually the result of a poor installation, particularly failing to have an anti syphon valve and a water trap in the system. Mine is still fine after more than 20 years!

[/ QUOTE ]I think this is unfair, mine broke after 340 hours (maybe less). I have anti-syphon valves, water traps, I always turn the sea cocks off.

They are available, but have you priced them /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif I had mine welded back up, I did consider modifying in the same way as the OP, but decided both had a weld and mine had enough meat to carry out a successful weld.

This is a really common fault and to suggest poor installation to me is insulting to be honest, I installed my engines and took great care to ensure they were fitted properly.
 
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Isn't there a misunderstanding about how these elbows work? Normally, the inner pipe is spaced-off of the outer pipe so that some of the gas goes outside the inner pipe and mixes with the water.

[/ QUOTE ] No, it is a solid weld and creating a seal between the water and the exhaust port. The inner pipe creates a sleeve to ensure water is not sucked back into the engine when it is stopped.

If mine fail again I am going to fabricate a whole new elbow with a inverted U bend and have the water enter on the bottom of the U. I considered putting a pin all the way through the bottom of the sleeve but decided against as the weld could still crack and water would seep in anyway.

Not a great design, and a fail cost me a years cruising budget or some new doors from chuchilo /forums/images/graemlins/frown.gif
 
Well there are certainly plenty of folk here who know far more I do about diesel engines and nobody has jumped in, so maybe I'm wrong.

Last Spring my muffler failed (stainless, drain plug was brass and had to remove) which meant taking off the exhaust hose from the elbow to the muffler. I took the opportunity to remove the elbow and discovered that it was all gooey inside -- like tar. The previous owner had told me of an incident when he grossly over-filled the sump (there is an oddity about the Yanmar 4LH-TE in this respect) and I suspected that the goo was due to that. I soaked the elbow for several days in strong caustic and that didn't do anything so I started to work on it with my Dremel-clone. The construction of mine was far more complicated that just one pipe inside another. The weld around the engine was not continuous. It seemed to me that the water was mixed with the gas at the point of water injection whereas the 'new design' here does not allow any mixing until almost the end of the elbow. My engine is probably very much more powerful than this one, judging from the sizes, but I am still surprised. I think we might find that these elbows are so expensive because they are not that simple.

Or, it could be that they are that simple in smaller engines (mine is 110hp)?
 
Agree entirely, Dogwatch. Cid's design replicates the Yanmar design intent perfectly. Exhaust gases do not pass through the outer annulus on either. Hence no passage of water over the top of the annulus, leading to stupendous crevice corrosion on the Yanmar design.
My elbow rotted through after 3 years. Engine installed on new AWB, istallation correct. Barrus paid for new elbow but only after hassle.
I was so shocked by all this that I now intend to remove and inspect annually.
 
I have a suspicion that people are being misled by what they see when they remove the old device. I was fortunate to work on a still-working elbow and could see how it worked.

This article covers the basics -- you need to scroll down a bit to see examples similar to this case. Note comments about blocked water passage holes; this new design has NO water passage holes.

http://www.yachtsurvey.com/exhaust_risers.htm
 
No, not misled. Eyes and brain in reasonable nick. Neither the rotted pipe or the brand spanking new one allowed exhaust gases to pass through the outer annulus.
On a 2GM20F, 2004 vintage.
As a matter of interest, which model was yours?

Oops, sorry, just noticed your previous post - Yes, it confirms that we are talking about different engine models. Yours sounds as if it is better engineered than GMs.
 
Fair enough. Sounds to me as though someone ought to start making cast replacements to a better design. Nice little business to run from home.
 
Sorry to disagree about the 'life'. Yanmar's own advice is check every 200 hours. Typically, they can rot out in a couple of years.

I don't know what the problem is but anecdotal evidence seems to show that the longer the engine is worked (such as in a fishing boat) the longer it lasts.

Ours has an average use time for last year of 47 mins per sail so 23-24 mins going on and off the mooring and is definitely 'short-lifed' we're on our third or fourth already!

And the installation is determined by the manufacturer as to angles of fitment. The Yanmar agent has, on our boat, fitted water traps, antisyphon etc etc.

It is just an absolutely appalling bit of engineering.

So much so that the local Yanmar agent makes up an alternative, out of cast-iron drain pipes that is bullet-proof. So it can be done. I'm sure it's just that Yanmar love the income from this stupid over-priced bit of tin!
 
Nice piece of engineering but I think I would drill a few holes in the inner pipe to allow the water to cool the exhaust gas before it meets the rubber pipe. The lack of holes will only be an issue at high RPM but thats when you need the thing to hold together!
 
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Nice piece of engineering but I think I would drill a few holes in the inner pipe to allow the water to cool the exhaust gas before it meets the rubber pipe. The lack of holes will only be an issue at high RPM but thats when you need the thing to hold together!

[/ QUOTE ]I was going to suggest the same thing. 3/8" holes all the way from the injection point? It would be very easy to make pattern and cores to do a decent cast job but it would be nice to run some proper tests before releasing the product. OTOH, what could possibly be worse than the present bodge (i.e. Yanmar's bodge)? As one poster said, a perfect example of a crevice corrosion risk. Cast steel will be much better, anyway.
 
Think that is the heart of the "problem". Many of these engines are used in small sailing boats and get very little use. They never really get hot and one of the causes of the corrosion of the inner pipe is because when the engine is stopped it can suck back water and vapourwhich corrodes the inner pipe.

Your usage pattern illustrates this well. When you come back after a sail, you run for a short time, turn it off and water vapour sits in the inner pipe doing its worst while you are not there!

You could, of course say that Yanmar should be aware of this type of usage pattern and design accordingly. However as I pointed out mine has lasted 20 years with similar usage, and I am sure there are thousands of engines doing the same.

Doesn't help if yours is one of those which does fail, but failures are not unknown on other engines. Basically the 1GM is a simple and reliable bit of kit with low overall running costs - even allowing for the odd exhaust replacement.
 
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