Exhaust Riser - Leaking

[Steve McGill]

Folks,
A few weeks ago I noticed an exhaust smell in my aft berth. Following the discussions and write-ups by many folks, especially Ron Hill and Stu Jackson I knew I may need to replace my exhaust riser. With the engine running I was able to feel exhaust gases escaping from the front of the flange where the pipe exits.

My boat was built in October of 87 (1988 model, 1500 hours)

My engine is currently winterized; yesterday I removed the fiberglass insulation from the pipe.
It appears that the threads of the pipe where it enters the flange at the top may be worn through. After a few applications of PM blaster I was able to remove the two top flange screws. I will need to move or remove my HX to access the lower flange bolt, after a few more applications of PB blaster I will attempt this.

From everything I have read I assume I have the original black pipe riser. Additionally I still have the ridged black wire reinforced rubber pipe into the aqua lift muffler.

These are my thoughts and plans, any comments or suggestions are greatly appreciated.

Is best to replace then try and repair my exhaust riser? once removed I will contact CY for a replacement and order a new flange and gasket/s from Torresen. Marine.

My HX is 3" in diameter, but the zincs that fit the screw are  about ¼" in diameter, this seems odd to me since the spare parts kit contains a much larger zinc (3/8"). Depending on the condition of the inside  I may also replace this along with all the hoses.

I can purchase the hump hose from Catalina Direct, however my current ridged rubber back pipe appears longer then 8" hump hose available.

Thanks,

Steve M.

[Mike Denest]

I've been through what you are about to do.  Remove the riser and send it to Catalina.  They'll remove the flange and put it on a nice new stainless steel riser.  Order the hump hose from Catalina Direct.  I ordered the 8 inch hose and trimmed it down to about 6 inches so the flange would fit.  It's not an easy job but it can be done.  good luck!

[Stu Jackson]

Steve, this is from the old "List" before the message board, and has some older info that may be of help in answertring the length fo hump hose.  YOU, when you install it, have to set the distance by the number of turns you put on the flange.  Great pictures, I have the same problem, but with a (relatively) new riser.  Gasket, riser, you MAY be able to use your old flange.  Clean, clean, clean.

See FAQs, too, as well as the Knowledgebase which is searchable as an Excel file.

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Exhaust Pipe Replacement
(for Hump Hose Information, see bottom of page)

Subject: Re: Exhaust Pipe Replacement
Several weeks ago there was a thread regarding the replacement of the exhaust pipe. I was looking into doing the same for our boat. I contacted Catalina direct and got the part number, price etc. from them. To my surprise they told me that their part did not include a flange fitting  to  mount to the engine manifold and that I would have to purchase the part   from  "Trans Pacific". At Trans Pacific they had no idea how the Catalina Direct  part was to attach to thier part, i.e threaded fitting or ??.
This has all been somewhat of a surprise to me, since my recollection of  the  discussion here on the list was that the new "one?piece" stainless steel  pipe was the way to go. It seems as though that this is in fact not a one  piece part. Since it isn't, I'm not so anxious to replace the exhaust pipe. I've checked  the pipe and it appears to be sound and well fitted. The only problem that I have is that the end fitting at the raw water inlet, has developed a pinhole  leak. I repaired it with epoxy in an overnight stop late last season, but  don;t want to rely on it for a full season. The part is about 6" long,  has a  threaded end that screws into the black iron pipe, has a 3/4" "Y" that  the  raw water hose clamps onto and a smooth end that the 1 5/8" hose clamps  onto  to take the wet exhaust to the muffler.
Does anyone know where I can obtain this end fitting? Or was it custom made by the last Owner ?
Frank,  Kik N Bak

Subject: Re: Exhaust Pipe Replacement
Frank:  There have been a number of exhaust Iron & Stainless riser articles in the past issues of Mainsheet . The (Universal part) flange at the engine that adapts to the exhaust riser (Catalina part) is not an item I'd trust to epoxy ? Mainsheet Nov. 98. Contact Jim Kennemore (925) 447?8616 and $35 you can get a bound book of the 1987?1997 past Tech. notes. It would also help, if in the future you identify your C34 by year and hull# ?? as all C34's are not identical.   
Ron,  APACHE,  #788

Subject: Re: Exhaust Pipe Replacement
From:   holder@unixg.ubc.ca (Barbara and Charles Holder)
The part you're describing is similar to one I had made when the  original exhaust on my boat failed due to corrosion at the weld between the 5/8 inch water injection pipe and the 1 1/4 inch nominal size pipe (actually 1 5/8 inch OD).
Rather than buy from Catalina, which can be a Border Customs nightmare  for those of us in Canada, I had a local fabricator, who could weld stainless steel, make up the whole thing out of screw coupled, stainless steel, schedule 40 pipe. The only welding required was to connect the water injection pipe to the last pipe section.
Next time, if there is another, I'll use schedule 80 pipe for the last  section where the water injection pipe is welded in. Schedule 80 pipe has a thicker wall but the same outside diameter. I'm fairly sure that the original Catalina exhaust was schedule 80 for the end section. There are two reasons for using the schedule 80 pipe: the hot gas and water form a fairly corrosive mix that attacks the weld heat altered steel and the screw threads remove quite a bit of the pipe wall reducing its strength perhaps too much.
By the way, I reused the coupling to the engine. It can be removed from the exhaust   pipe but might require a lot of heat, a very large pipe wrench and a large mechanic's vice. The heat, and I'm taking about to dull red, makes the coupling expand loosening (a relative term) the joint. A couple of strong friends would be a useful addition for this part of the job.
Regards
Charles Holder,  Discover,  #617,  1988

Subject: Re: Exhaust Pipe Replacement
From:   ronphylhill@erols.com (James R. Hill)
Dave, The first step in replacing your exhaust riser is to drain the coolant through the starboard side petcock near the front of the engine.  Squirt some liquid wrench on the three nuts that hold the riser and flange to the back of the engine and let it sit over night.  I believe these nuts are 7/16" and are best removed with a box end wrench rather than a socket, especially the one underneath.  After you remove these nuts, you have to undo the raw water hose from the riser and the two clamps from the inlet exhaust hose to the muffler.  With some gyrations the flange/exhaust riser will come out thru  the engine compartment.
To reassemble the first step is to put the flange in a vise.  Screw the exhaust riser into the flange until you get the angles aligned properly (use the old exhaust riser and flange as your pattern).  Then back off the riser counting the number of turns until it is all the way off.   With the flange still in the vise, treat the riser threads with some muffler patch and screw back in the flange the same number of turns.  Remember don't over tighten because you don't want to have to back off (you may break your seal).  You want to end up tightening it to get the proper angle.  Ensure that all of the gasket material is off of the exhaust/reservoir casting on the back of the engine.  It's a real bear to get in there and make sure the surface is clean, but quadruple check this or you will not get a good seal and lose your coolant (when you refill) and have to start over with a new gasket. Make a dry run without the gasket just fitting the flange/riser assembly in place.  As I mentioned in the Nov 98 Mainsheet Tech Notes, try the "dollar bill test."   It's more important for a 25XP with the larger diameter heat exchanger than the M25, because the factory may have wrapped too much insulation in that area where the riser goes over the heat exchanger. I couldn't get the flange to completely seat until I cut out some of that insulation.  If you can pass a dollar bill between the riser and the heat exchanger, you are in good shape.  If you can't, whittle away some insulation. Also measure the length of hose that you'll need between the riser and the inlet to the Aqualift muffler (with a new riser it may not be the same distance as it was with your old riser).  After you are sure the flange/riser is going to seat and that surface is absolutely clean, place the gasket on the three studs.  I even used some of the muffler patch around both sides of the gasket to make sure I had a good seal.  This is a perfect time to install the single hump hose which I wrote up in that same Mainsheet article and again in the Aug 99 issue( the 81/2" hose from the factory is $33.75).  Up to this point, disassembly and reassembly has been a one person job.  Now you need a second pair of hands.  As one person aligns the flange with the three studs on the back of the engine, the other person aligns and inserts the single hump hose into the flange and muffler inlet. Tighten down the three nuts to secure the flange, double clamp the single hump hose on the flange and muffler ends.  When I attached the new raw water hose from the anti?syphon, I made it a little bit longer than the original factory installation so it could flex a little and put less strain on that welded nipple that goes into the riser.  Reclamp that hose and you are ready to refill the reservoir with coolant (50/50 Prestone).  To ensure that you don't have an air bubble in your internal cooling system that goes through the water heater, remove the inlet hose to the thermostat housing.  Insert one of those Par Junior Pumps and with the pump exit pointed into the reservoir, keep pumping until you have coolant being pumped back into the reservoir.  Remove pump and insert hose into the thermostat reservoir and tighten the hose clamp( you shouldn't have to "bleed" that system as all of the air has been purged) .  Recheck that the reservoir is full & replace the cap, start the engine and check for any leaks.  You should be in goodshape.    Hope this helps.
Ron,  APACHE,  #788

Subject: Re: Exhaust Pipe Replacement
From:   RPDIII@aol.com
Dave:  The letter written to you about draining the expansion tank is good advice and a good way to drain the tank.  I have replaced my exhaust system twice and I only have this to offer.  Using the drain plug does drain the tank however when you remove the gasket for the flange the remaining fluid will drain out the rear of the tank.  If you use the drain plug the fluid (may) end up soaking into the engine compartment sound proofing.  If you drain it from the rear it will fall onto the fiberglass and end up in the bilge.  I also suggest taking this opportunity to wash the tank out to remove whatever particles have settled in the bottom of the tank over the last 11 years.Just a thought because you will have to replace the gasket no matter which way you go.  You will also notice the gasket has a stamp on it indicating which side goes against the tank, (very important).
Good Luck;
Rich Dwyer,  Rebellious,  #328

Subject: Re: Exhaust Pipe Replacement
From:   davis_707@yahoo.com (dave davis)
Ron, I did the draining today and caught maybe 95% of the coolant. I used a small plastic bendable cup and used my finger to stop the flow every time the cup filled up. I also spayed the the bolts with liquid wrench.
Dave

Subject: Re: Exhaust Pipe Replacement
Hello Ron. Our exhaust riser on our 1988 C34 (#542) finally cracked just below the raw water injection nipple. I reread all the info in the tech notes and mail list, and called Catalina to order a new riser. They said I'd have to send in the old one and they would fabricate a new one using the old one as a pattern. Greg in parts said turnaround would be around a week and a half. Was this your experience? I was fantasizing that they would send a new one right out. Any reason to send it to Catalina if I can have one fabricated locally?
Steve,  C34 "Sunshine" #542


Subject: Re: Exhaust Pipe Replacement
From:   ronphylhill@erols.com (James R. Hill)
Steve : Although I ordered a new ss riser I took the old one to a welding shop and they put a ss weld over the hair line crack ? so I now have a spare.  I'd take yours off and take it to ss welding shop and see what they say.  I'm sure that if the crack isn't to bad they can repair it for $10? $15.  With the money you saved call Greg and order a single hump hose (same length of your old hose).  Also install a new hose from the anti syphon to that nipple.  Make sure that the new hose has some flexure in it so it  places the least amount of vibration stress on the repaired nipple.  Make SURE you have all the old gasket off the engine or you'll screw up the new gasket on reinstallation.  It's hard to get to so you'll need a mirror.
When I ordered my new riser Catalina only wanted certain measurements to make up my new one.  They could have had an unhappy customer because the new riser didn't fit and now require they send the old one back.  If you send your old one to them as a pattern I'd ask for the old one back, repair it and have a spare.
You could have one made locally, but I'll guess that Catalina will have the best price.  A few thoughts.
Ron,  APACHE,  #788

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more to follow in second post, this exceeded the limit on the board.

[Stu Jackson]

Part II

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Subj:    Re: [C34]
From:   holder@telus.net (Charles & Ba Holder)
My suggestion would be to fabricate from schedule 80 stainless steel screwed pipe and bends.  That way you only have to weld the injection pipe into the last short piece of pipe. I found the same piece rotted out frequently, probably due to heat alteration of the metal when welding and the presence of heat and salt water.  Using screwed fittings enables one to replace one part and means a lot less expensive SS welding.  Lots of pipefitters can cut and thread pipe.
Two cautions:  you'll need to use a thread sealer ? I used regular exhaust paste spread on the pipe threads;  welding in the injection pipe will distort the pipe section to out of round ? have the welding done first, then the pipe cut and threaded.
Schedule 80 is thicker than normal steel pipe and provides more metal after cutting the screw threads.  As to which stainless steel grade, I'd suggest regular marine grade 18/8.
Charles and Barbara Holder,  holder@telus.net

Subject: Re: Exhaust Pipe Replacement
From:   davis_707@yahoo.com (dave davis)
Hi Mike and George, When I bought my Exhaust Manifold from the factory, they wrapped it with lots and lots of insulation. I'm not sure , but I think the main function is to protect YOU from getting burned. The pipe would run cooler if it had a place to radiate the heat. But I left all the wrapping in place. The results were such that it would not pass the "dollar bill test" that Ron use to talk about. That is, there must be a space between the manifold and the heat exchanger so the they would not rub each other and cause more problems. To solve that problem, the yard man took off the HX and bent the support flange about 1/2?1 inch so that there would be a good clearance. Hope this helps
Dave

Subject: Re: Exhaust Pipe Replacement
From:   ronphylhill@erols.com (James R. Hill)
Mike : As far as all the wrappings ? they are there to keep all the HEAT inside the riser and not let it get into the interior of the cabin.  TRIPLE check that the mounting flange on the engine to insure it is absolutely clean of old gasket material.  Then check this again!!  If the welding shop was capable of doing a good job of stainless welding, you should be good for another 5?10 years ? if the rest of the flange piping is OK.  Make sure that you have a slack bend in the raw water line that empties the heat exchanger water into the nipple in the riser.
The tip from your mechanic is correct on worrying about a scored or pitted surface on either the engine / riser flanges.  What I used for a "liquid gasket" material was muffler patch paste.  It's the only material I know of that could stand up to the exhaust heat.  Mine is sealed and w/o leaks, 3 yrs later.
Ron,  APACHE,  #788

Subject: Re: Exhaust Pipe Replacement
From:   davis_707@yahoo.com (dave davis)
  Additional Options...  Notify me of reGeorge:  The exhaust flange for the Universal 25 XP is Part # 298599-R14. It cost me $51.90 in Oct.99. From SEA POWER Oakland CA. 510?533?9290 Ask for Colin, the parts man. Make sure they install a rubber hose that has a hump to take up the vertical vibration stress. Good Luck,
Dave

Subject: Re: Exhaust Pipe Replacement
From:   davis_707@yahoo.com (dave davis)
George, I worked with Ron on this problem and at the time we gathered information about engine hours vs.failure for the stainless and for the iron exhaust manifolds. If you would like, I have the CY drawing of the replacement Stainless which I could send you by Smail. Some skippers went out and replaced the manifold with sections they rigged from galvanized iron but I have not heard back how long they lasted. To get a replacement we need to know your hull # and the length of the rubber hose that connects it to the Exhaust riser. You may also need the flange that connects the the exhaust manifold depending how hard it is to remove. I replaced mine. I can tell you where to purchase a new flange. Or your rigger might have all this information.
Good luck, I hope this doesn't ruin your summer plans.
Dave Davis

Subject: Re: Exhaust Pipe Replacement
GeorgeM2nd@aol.com wrote:
For information only ? my exhaust riser manifold failed at the first 90 deg. turn from the engine mounting flange.  This failure (and action) was  addressed by Ron Hill in the 1997 tech notes index. I do not have the newer stainless manifold.  Total engine hours ? 748
George,  OK?3,  1987 #339

Subject: Re: Exhaust Pipe Replacement
From:   ronphylhill@erols.com (James R. Hill)
George : If you have a little time & are a Boat US member you can order that same flange for $43 through their engine parts ?? Mainsheet Tech notes a couple of years ago.  A thought.
Ron,  APACHE,  #788

Exhaust hump hose

Subj:     Re: Exhaust hump hose
From:   dnkkay@prodigy.net
I have an exhaust leak from my exhaust manifold to the Aqua-lift muffler.  I pump water into my bilge when the engine is running (Universal Model 25).  It's a short piece of hose (about 5 inches) that seems to be leaking.  I don't think I can replace the hose without removing the exhaust manifold/pipe.  The nuts and studs that hold this manifold seem so rusted that I'm afraid to tackle them.
Has anyone tackled this job before?  I'm wrapping it in a vulcanizing tape, then wrapping inner tube around it (and using hose clamps to hold it down) for a temporary fix.
Thanks
Ken Kay,  Watercolors,  Long Beach, CA

Subj:     Re: Exhaust hump hose
Gary Wilson wrote:
Hi,  I want to install a hump hose between the manifold and muffler, but    cannot   find a source for the part (1?5/8" dia).  I can't put my finger on Ron   Hill's article to   double check, but I have had no luck at the local marine diesel dealers,   hose suppliers or West Marine.  They checked in the manufacturer's  catalog   (Gates) and it is not listed.  I checked with the Catalina factory and    David   Graas   said the hump hose they stock will not fit the C34 application.   Does anyone know of a source?
Thanks,  Gary Wilson,  Childsong #138

Subj:     Re: Exhaust hump hose
From:   ronphylhill@erols.com (James R. Hill)
Story on the Single Hump Hose:  Last June Gerry Douglas told me about this when I  talked to him when I was ordering a new stainless steel exhaust riser.   After installation of the new riser and the new single hump hose on my 1988 hull #788  C34, I wrote Gerry Douglas on 27 July ? that it was a great modification but it could only be changed out with a new exhaust riser.  "The new hump hose is only  5?1/2 inches tall and the old hose I removed from the old SS riser is 8?1/2  inches.  The new hump hose would have to be 8?1/2 inches tall to make it fit with  an old riser system."  (My old riser was stainless steel with a crack in the  exhaust water nipple that joins into the exhaust riser just above the muffler.)
In Nov 98, I received my first inquiry on where to get a single hump  hose for the  Catalina exhaust system that I had mentioned in the Nov Mainsheet.  Again I wrote  Gerry Douglas and reminded him of our previous correspondence in July that the  single hump hose I received from Catalina parts was 5?1/2" long and with the new  riser it fit well.  However, IF I had wanted the single hump hose for my old  stainless riser the length had to be 8?1/2" long.  I also told Gerry that I had  forwarded a copy of our correspondence to Marvin in Catalina parts so the parts  department wouldn't sell a hose that might be 3" too short to a customer.  In the  meantime I contacted Rich Becker, General Manager of Trident Rubber and found out  that a 1?5/8" inside diameter silicone single hump hose is a non?standard  diameter size for Trident and made only for Catalina.  They keep none in stock.
At this time they only make this hose in a 5?1/2" length per Catalina's   request.  Trident would gladly make an 8?1/2" length if any individual wants to buy 50 or  more of them!  Later in Nov I relayed this new Trident information to Gerry  Douglas and recommended that they might buy the longer hose which Gerry said they  would do on their next purchase.
The key to the puzzle is to measure the distance between the Aqualift  muffler and  the base of the exhaust riser and determine its length.  Then contact Marvin at  Catalina Parts (1?818?884?7700) and see if they have a single hump hose of the  length that you want.  If the hose length is too long, you can always cut it off. Hope this helps.
Ron Hill C34 Mainsheet Tech. Editor

Subj:     Re:  Exhaust hump hose
From:   holder@unixg.ubc.ca (Barbara and Charles Holder)
Your note about Catalina Parts is intriguing. I just bought two hump  hoses from them, one to use and one as a spare. They fitted perfectly. They are actually made by Trident and are an off?catalogue item. That means the normal parts suppliers will deny their existence but if you force them to contact Trident they'll find they do exist. The size I obtained is 1 5/8 inch diamater to fit a 1 1/4 nominal pipe size exhaust and it is about 6 inches long.
My boat is a 1988 Cat 34 fitted with a Universal 25XP engine.
Regards,  Charles Holder

Subj:     Re:  Exhaust hump hose
From:   FRANKKUL@prodigy.net (Frank Kulscar)
Well, it seems that my spring projects are coming to a close.
Exhaust pipe replacement:  Couldn't buy into Catalina Direct's stainless steel $141 super tube. My  opinion is that its a flawed system since there still remains a black iron (or galvanized) pipe from the manifold flange and the elbow to the s.s. tube. I made ours from all galvanized for about $25 from a local plumbing  store. Sealed each joint, tested it and it works fine.
Good luck on finishing spring projects!
Frank,  Kik N Bak

Subj:     Re:  Exhaust hump hose
From:   ronphylhill@erols.com (James R. Hill)
Tom : The only place to get the 1?5/8" single hump hose is from the Catalina factory.      Trident Co. only makes that diameter hose for Catalina.  I think it's about $30.  Let Marvin or Greg in parts know the length you need . When you get ready to put it on it let me know and I'll give you a few installation tips.
Ron,  APACHE,  #788

[Roger Blake]

Oh my Stu...I think you've out done yourself (how is that even possible??). All I can say, in awe, is thanks for the support you have provided, and continue to provide to those of us with less knowledge (but desire to learn more). There are many things I've learned from you and Ron that have assisted me in ensuring a safe and sound C34. Thanks for all your efforts!

[Ron Hill]

Steve : I'll guess that a previous owner had a stainless riser problem and elected to go for a black pipe replacement.  Stainless became the factory norm in mid 1987.  From your picture they used a galvanized elbow.
Black pipe isn't all that bad, but doesn't last as long as stainless.  Galvanized last even less.
Get youself a single hump hose from Catalina so that when you put the new riser on there's a cushion between the riser and the muffler intake. 
You might also think of "stake welding" the nipple in the riser from the inside(as well as the outside) as that is the weakest part of the riser system. 
A thought.   

[Steve McGill]

Folks,

Additional information and pictures detailing my exhaust riser leak.

The three bolts from the heat exchanger were easily removed after spraying PB Blaster 3 times over a two week period. Once I removed the two screws for the bracket for the heat exchanger this cleared the way for me to have complete access to the bottom bolt of the flange.
Once the gasket from the exhaust flange and manifold is broken you will have a loss of coolant. I utilized three roles of paper towels, plastic bags and paper cups to catch all of the antifreeze. I am sure there is a way to drain the coolant, but for this exercise I did not investigate it.

I removed the clamps from hump hose on the aqua-lift muffler and was able to remove the entire riser through the engine compartment.

Pictures:

1. Complete riser removed.

2. Riser as it screws into exhaust flange, the pipe had separated from the flange as it threads into the flange. Only about one tenth of the pipe was still attached.

3. Rear view of exhaust manifold where flange with exhaust riser attaches.

I had assumed that my riser was made from cast pipe; I was surprised when I discovered that the pipe is brass. You may notice this where the pipe threads enter the fittings. There were 4 threads of pipe in the flange, with a Dremel tool and cut-off wheel it was easy to remove the threads from the broken pipe.

My plan; (always looking for suggestions)

As suggested I will contact Catalina Yachts to build me a stainless duplicate. I will provide them the flange and riser to insure an exact size match.

Order gasket for the exhaust flange, I also use some type of RTV cement.

Order proper hump hose from Catalina Direct.

Thanks.

Steve McGill

[Stu Jackson]

Steve, nice pictures, thanks.  The easiest way I've found to remove coolant from the manifold is to disconnect one of the fresh water hoses and drain it out.  I also understand there's a petcock somewhere on the manifold, and some have suggested that, but noted it didn't get it all out. 

[Craig Illman]

Steve - I have a petcock on the starboard side of the block just behind the raw water pump. It drains a substantial portion of the coolant, but not all in the heat exchanger or the loop to the hot water tank. (M25-XPA)
Craig

[Mark Elkin]

So, now it's my turn.  Just before the holidays, I was out enjoying the water.  Not enough wind yet that morning to strictly sail, so the motor was running.  I went below and noticed a strong exhaust smell and water on the cabin sole.  Opened the door to the head and it was filled with steam.  Oh, I should mention that this was the same moment that both my bilge pump automatic float switch and the manual bilge pump chose to break.  And I was single-handing.  Fortunately, the manual activation switch for the electric pump worked!  As quick as possible, I got back to my slip and shutdown everything.  Then spent the remainder of the day cleaning the mess and fixing the bilge pumps.  (There's another MB discussion there, stay tuned.)  Anyway, the holidays came and we left town.  I took my laptop and tech notes CD and did a lot of reading while in various airports.

Finally this last week, I fired up the engine and nearly instantly found the problem.  Time to pull and repair or replace the exhaust pipes.  Thanks to other owners' experiences, I knew to drain the fresh water reservoir.  And because I'd already replaced the 2" heat exchanger with a 3", it meant getting access to the lower flange bolt would be a chore.  So I drained and de-hosed the HX and moved it too.  Fortunately, the nuts came off the flange very easily.  Getting the hose off the muffler was a bit trickier but it finally let loose and I maneuvered the whole thing out.

With the assembly in daylight, it was easy to see the problem.  (Picture 1.)  BTW, the hole you see is about 10x bigger than the original hole.  The metal just crumbled when I pressed on it with my finger.

Looking at the entire assembly, though, just didn't seem right though.  From all the C34IA reading, this exhaust system appeared to be non-standard.  Sent a picture to Ron and Stu.  (Picture 2.)  They both confirmed it: never seen anything quite like this one before.  I guess the original owner of Y.Rose already did an exhaust job -- but before the stainless steel riser and hump hose became the standard.  That probably explains why the flange nuts came off so easily -- the PO did a proper job preparing them with anti-seize during the last time.

Anyway, I'm now faced with either replacing the corroded piece or switching to the whole new stainless and hump hose system.  And I'm sure the latter means additional "rework" due to other improvements I've made that certainly will occupy the same space that a new SS & HH system will use.  (Simple anticipation of Murphy's Law here.)

[Craig Illman]

Mark - With that design, I'd be real worried about getting raw water into the cylinders with just the slightest delay in starting.

Craig

[Ron Hill]

As I mentioned to Mark, the previous owner had the raw water entering the wrong side of the inverted "U".  Like Craig I'm surprised that raw water didn't get into the cylinders. 
Anyway it looks like Mark is well underway on getting it straightened out.   

[Mark Elkin]

As Ron mentions, I had expressed a concern about the raw water running down the wrong side of the "U", based on the location of the input port.  Well, I tested it -- in small increments, poured fresh water down the hose and waited for it to emerge from one or both sides.  It only came out the correct end.  So that suggests some kind of channel inside the "U" to direct the injection water.

And just now, I was finally able to get the corroded elbow loose.  It wasn't budging for the last several days, but the Nigel Caldwell approved, time tested method worked:  whack one of the pieces with a hammer and then squirt with liquid wrench, and repeat twice or thrice daily.  So with the elbow out of the way, I can see into the "U" and there's a definite 2nd channel to direct the raw water into the exit side and away from the engine's exhaust manifold.

[Steve McGill]

Folks,

I received my replacement exhaust riser from Catalina. They were a pleasure to deal with and performed quality work. I removed some of the insulation on the lower portion to allow sufficient clearance with the heat exchanger.

I cleaned the flange and the manifold mating points so that both surfaces are smooth and clean.

In addition to a new replacement gasket I am trying to determine if a gasket sealant of some sort would be beneficial. I have read all of the available posts that mention using "High temp" RTV silicone or muffler patch or this or that or nothing at all.

I think I subscribe to the camp that a gasket sealant of some kind would be beneficial.

I assume that the gases from the manifold are greater then 650 degrees and all of the gasket materials I have seen are less then this.

For the folks that used a gasket silicone,RTV material or muffler patch compound do you recall the brand name and type?


Thanks,

Steve

[Ron Hill]

Steve :  I used muffler paste, but I think that the RV Hi-Temp isn't hi enough.  So why don't you try nothing!!  If the coolant stays in the reservoir and you don't feel exhaust escaping then you have a great seal with just the new gasket!!

I hate to be the bearer of bad tidings, but I believe that your boat is missing the "Wiring Harness Upgrade"!!!!!!!!!  I note in your first picture a bunch of black electrical tape wrapped around what suspiciously appears to be one of the two 8 pin trailer connectors!!  I should have caught that back on 22 Oct - sorry!  If I am correct you need to make that upgrade before that connector shorts out and your boat burns up!!  This is serious! 
There literally has been MANY MANY posts and articles telling owners to make that upgrade.  Your boat most likely has a volt rather than an ampmeter, but it makes no difference - get the upgrade from Seaward and get it installed ASAP.