[C320-list] Yanmar 3GM30F Exhaust Elbow/Riser

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Dennis Cookson

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Mar 24, 2021, 5:33:44 PMMar 24
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I am thinking about replacing, or at least inspecting, the exhaust elbow on our 1999 Yanmar 3GM30F as its age and condition are unknown. It seems to be a non-standard construction, unlike any Yanmar part I can find, with a U-shaped riser which is fully insulated with a woven thermal sleeve of unknown material, possibly fibreglass.

I’ve uploaded a photo of this elbow/riser <https://c320.org/mediagallery/media.php?f=0&sort=0&s=20210324212234253> to the Technical Photos gallery.

It roughly resembles the shape of the “Exhaust Riser C-320” on the Catalina Direct web site which I see is made of stainless steel. The raw water inlet to this riser is located well away from the exhaust manifold, on the downhill side of the ‘U’ close to the connection to the rubber hose that leads to the waterlift. The fact that the riser has to be insulated makes me wonder if the water is actually used to cool the pipe, i.e. is it essentially a dry riser where water is not used for cooling but just for reducing exhaust noise. In this case, perhaps there is less risk of a failure causing water to enter the

I’d be grateful for any advice or information re the following questions:

- is this part prone to catastrophic failure from internal corrosion, in the same way that the original Yanmar mixing elbows are? Anyone had that experience?
- what lifetime in terms of age or engine hours can reasonably be expected?
- if it needs to be replaced, must it be replaced with a similar custom part like the one on Catalina Direct, or it is ok to use the Yanmar 128370-13610 Mixing Elbow Riser Kit? This has a much tighter bend with water input very close to the manifold. (I’m assuming that the riser needs to reach a specific height above the water level at all angles of heel - this arrangement would be more compact.)

Dennis Cookson
Catalina #577







Allan Field

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Mar 24, 2021, 6:16:53 PMMar 24
to C320...@catalina320.com
Dennis - My recommendation would be to contact a Yanmar dealer directly,
such as Bay Shore Marine in Annapolis, MD, and work with them for a
replacement. On our old C320, they furnished a perfect drop-in replacement.

Allan S. Field
Sea Shadow - C387, #103 (formerly C320, #808)
Columbia, MD

Troy Dunn

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Mar 24, 2021, 6:42:54 PMMar 24
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Been wondering similar thoughts. It appears that the stainless version is
less prone to fail prematurely. I have no idea what time frame or number
of hours is considered premature...

Troy Dunn
Hull#514

Dave Hupe

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Mar 24, 2021, 7:33:10 PMMar 24
to c320...@catalina320.com
Dennis-
Check out the Yanmar exhaust elbows here Yanmar 3GM30 parts (parts4engines.com)

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Yanmar 3GM30 parts

A wide selection of Yanmar 3GM30 engine parts including overhaul kits, gaskets, oil and fuel filters, gasket sea...
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I've used this United Kingdom source for OEM Perkins engine parts with excellent success and price (even including shipping which was very reasonable).  
They are very responsive if you email them with a question. 
Dave Hupe
1994 C320 (#32)Perkins Perama M30 Engine



Graeme Clark

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Mar 25, 2021, 3:12:35 AMMar 25
to C320...@catalina320.com
Dennis
I have the same on my 1996 #366
Rather than a woven sleeve, mine has a fibeglass woven “wrap” of 2” wide tape wound around it.
When I bought the boat I could see some rust staining on the exit side so I unwound the wrap and the elbow looked awful!
I unbolted it and the good news was that internally it looked vey good. No sooting up either.
I used a wire brush and it cleaned up really well, so the poor appearance was just surface corrosion. The riser is stainless .
I suspected a tiny crack may have developed where the water inlet joined the main exhaust tube so had that rewelded for a couple of beers!

All now good

However I too struggled to find a replacement (especially as I’m not in the USA) and wondered if the other type would be suitable. In the end, had the repair not worked, I was going to get a local fabricator/welder to make me a replacement.

I believe the wrap is simply insulation to stop damaging levels of heat until the water gets injected.

I actually think it a simpler and more elegant design that the other type, with less to cause problems

Hope that’s useful

Graeme

Sent from my iPad

> On 24 Mar 2021, at 21:33, Dennis Cookson <den...@cooksons.net> wrote:
>
> I am thinking about replacing, or at least inspecting, the exhaust elbow on our 1999 Yanmar 3GM30F as its age and condition are unknown. It seems to be a non-standard construction, unlike any Yanmar part I can find, with a U-shaped riser which is fully insulated with a woven thermal sleeve of unknown material, possibly fibreglass.

Dennis Cookson

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Mar 25, 2021, 6:23:29 AMMar 25
to C320...@catalina320.com
Thanks for all the replies on this question, very helpful as usual. I wasn’t sure whether I had an original exhaust elbow fitted by Catalina when the boat was manufactured, or a custom replacement sourced by a previous owner, as it certainly doesn’t look like any standard Yanmar part.

From the replies it looks like I’m not alone with this fully insulated inverted U-shaped riser, so that leads me to suspect it is in fact an original fitting, so likely over 20 years old. It’s still working fine, so my concern is only for preventative maintenance, not an urgent repair.

Graeme, your reply is especially useful as your elbow may be even older and still in good shape after a little cleaning. Good to know that it was manufactured in stainless steel too. Here’s a question for you: when you unbolted the part and looked inside, was it just a single hollow tube, or was there a double skin with the water circulating in a separate outer channel around the encased exhaust gases? If the former, then this is presumably a simpler construction without the possibility of an inner sleeve corroding unseen and potentially breaking away without any warning, as is known to occur with the original Yanmar elbow. My hunch would be that there would be some evidence of visible corrosion or leakage that could be detected on this part prior to a major failure, and much less risk of water being sucked back into the engine. However, the tightly fitting thermal sleeve makes external inspection rather difficult!

I plan to give Catalina a call to get more info on this part and will share any further findings.

Best regards,
Dennis
Catalina #577


Graeme Clark

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Mar 25, 2021, 6:30:43 AMMar 25
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Dennis

It is a single wall tube. from memory quite thick, at least 1/16th maybe 1/8th inch thick. I have some photos somewhere. I’ll upload and post the link

For what its worth I’m pretty sure the previous owner had never removed this before. there was no carbon build up at all within the tube (obviously it was ‘sooty’ but no discernible thickness). I put this down to the gentle curves allowing a smoother free-er flow of gases, but maybe thats just wishful thinking!



Graeme

Graeme Clark

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Mar 25, 2021, 6:48:48 AMMar 25
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Dennis

Further info:

I cant find any useful photos, but the ones I do have, when i first removed the wrapping, would elad you to believe that this could not be stainless steel. A rough rusty colour all over. But of course it was never polished stainless, just (as far as I can see) standard industrial stainless pipework as used in chemical plants and so on. Its all put together with screw threads (tapered pipe threads i think). the water injection is just - basically - a shaped oval hole cut near the discharge end, into which a smaller tune is inserted at an angle and welded. It was this weld that was leaking and which I had ground out and remade.

By the time I had taken a wire brush to it it looekd great again (not shiny, but clean) but no doubt more heat will have blackened it back don again by now. The advatageb of the fibreglass wrap - rather than a sleeve - is that you can remove it in situ anytime you want to chaeck the external condition, and then re-wrap it (wear a mask as dust is very irritating!).

Before I took it off the engine I spent a lot of time looking at how to build a replacement from standard components, before deciding - once I had removed and inspected it - that a repair would be good for a few more years (or even decades!) Its the inverted U that is the problem to source as it boith bends and twists!


Cheers

graeme

Dennis Cookson

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Mar 25, 2021, 11:31:29 AMMar 25
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Thanks for the additional info, Graeme, which is reassuring. Given that the riser is indeed a single walled tube, it seems unlikely that this design could suffer a catastrophic failure without some advance warning, which is my main concern. A slow leak would become apparent, and having a CO detector in the aft cabin is a wise move. In the first instance I think I’ll source a thermal wrap as you suggest and remove the existing sleeve to get a better look at the surface.

In the event that we need to install a more standard replacement at some point, this HDI Marine kit <https://www.parts4engines.com/yanmar-3gm30-stainless-exhaust-outlet/> from Parts4Engines looks like the best bet.

Regards,
Dennis
Catalina #577
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