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

[Graeme Clark]

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

> On 25 Mar 2021, at 10:30, Graeme Clark <cg at skyflyer.co.uk> wrote:
> 
> 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
> 
> 
>> On 25 Mar 2021, at 10:23, Dennis Cookson <dennis at cooksons.net> wrote:
>> 
>> 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
>> 
>> 
>