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Exhaust Riser "mixing elbow" questions

Jun 2, 2014
348
Catalina 30 mkII - 1987 Long Beach Shoreline Marina
I’m dealing with a new low power/low RPM under load issue described in my other thread. I’m pretty convinced at this point that I need to check the mixing elbow for carbon blockage. I have a ton of questions. I have also been reading a lot.
The consensus seems to be that I should not expect to be able to clean or repair it for any extended time and should just plan on replacing it. I’ve had the boat for 5 years. 1987 mkII.
There was a bit of black soot sprinkled on the floor below the elbow area and on top on the muffler. I’m guessing that if the elbow has developed lots of carbon buildup that it’s also likely to have pinholes and deterioration.
I know nothing about it aside from what I’ve read online. I understand how it works. I have never touched one.
there is a blue rubber boot clamped on the muffler side, there is very thick thermal wrap over the rest of it.
Catalina Direct has a bunch of different ones that say they’re all for my engine. M25XP.

If I’m going to dive into removing it, should I just expect to replace it? Or is there any chance I can clear it out and re-install it and be good for any length of time?

is it worth trying to fabricate a hardware store pipe version I’ve read about? Or should I just buy the one from CD?
If I buy one from CD, I’m assuming I’ll need all new thermal wrapping? Where do I get that? CD?
Is that blue rubber boot I see just a coupler between the elbow and muffler?
Is there anything else special I would need to know?

I have a secondary fuel filter mounted to the wood cover that would need to slide out to expose access to the elbow. It looks difficult to get to the mounting bolts and I can’t slide it out without unmounting it or disconnecting the fuel lines.
This looks like a relatively big project for me alone. I’m not an expert mechanic but I’m handy.
Please, any advice would be appreciated. Thank you!
 
Feb 21, 2013
402
Hunter 46 Point Richmond, CA
You might some answers to your questions in the links below. Good luck.

 
Jul 7, 2004
6,358
Hunter 30T Cheney, KS
The hardest part of replacing mine was breaking the rubber hose loose. I bought a stainless steel one on ebay.
 
May 20, 2016
2,890
Catalina 36 MK1 94 Everett, WA
CD won’t sell the mixing elbow without the wrap. I went with the CD rather than making my own because of time constraints. The hardest part of the job is getting the old riser unscrewed from the exhaust manifold adapter. You might consider ordering one at the same time. Don’t forget the gasket.

Les
 
Jul 7, 2004
6,358
Hunter 30T Cheney, KS
CD won’t sell the mixing elbow without the wrap. I went with the CD rather than making my own because of time constraints. The hardest part of the job is getting the old riser unscrewed from the exhaust manifold adapter. You might consider ordering one at the same time. Don’t forget the gasket.

Les
I bought 2 ginormous wrenches at Harbor Freight. They hang on my garage wall now collecting dust.
 
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Jun 2, 2014
348
Catalina 30 mkII - 1987 Long Beach Shoreline Marina
Okay, let me get this straight... If I buy one at CD, they come already wrapped? So, all I should need is the rubber coupling hose and gasket?
 
May 20, 2016
2,890
Catalina 36 MK1 94 Everett, WA
Okay, let me get this straight... If I buy one at CD, they come already wrapped? So, all I should need is the rubber coupling hose and gasket?
Nope as soon as you order one they tell you you must also buy the cover. Why they don’t bundle and up the price is very deceptive to my way of thinking.

The hose should be silicone and is called a humphose
 
Feb 26, 2004
20,918
Catalina 34 224 Maple Bay, BC, Canada
Here's a long article I wrote for Mainsheet magazine a few years ago. The Catalina exhaust riser is completely different than Yanmar elbows. The Catalina elbow is a 1 5/8" OD pipe with a 5/8" OD NIPPLE welded to it for water injection. It usually fails at the weld between the nipple and the main pipe - guess why? The records of expected life expectancy are all over the place, but generally in the range of 1,000 to 1,500 hours, sometimes more (21 years of C34 ownership and 32 years of records). The Tips & Tricks here below may help you, and reflect exactly what Les has been trying to tell you. Some of the items are specific to a C34, not a C30, but the concept is the same. And CD has different risers for your M25XP BECAUSE the same engine was installed on different boats, so the riser "pipe" is different for different boats and muffler locations, that's why.

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Muffler & Exhaust Riser Replacement - 2015

There have been quite a few Mainsheet articles and C34 Tech wiki posts about the work involved in these tasks. Ron Hill’s classic November 2001 Tech Notes detailed his muffler replacement. My own February 2004 Tech Notes discussed our first riser replacement at 1,390 engine hours. This article discusses the lessons learned and Tips & Tricks of the work that my son, Morgan, and I did in September 2015 at 2,938 engine hours, 1,548 hours after our last new riser.

Muffler: The inlet and exhaust ports of our OEM muffler had been deteriorating for many years and had begun to seriously leak. Of course, we had installed the hump hose when we did our first exhaust riser replacement in 2003. I had reported on the Forum that I had attempted to rebuild the inlet port with Marine Tex, and that Morgan and I had replaced our 17-foot long exhaust hose in February 2012. The exhaust port was not so bad. We were able to obtain a replacement muffler for just the cost of shipping ($40) thanks to a generous fellow sailor (right here on sbo!!!) who was repowering his Catalina 30, and had made his old muffler available to us. A new muffler from Catalina Direct is $375.

Old Muffler Removal Tips & Tricks: After removing everything from the aft cabin, I spent a day removing the heat exchanger and taking out the four screws holding the old muffler down. We took an old cushion and laid it over the prop shaft. Many years ago I bought a small ratcheting screwdriver to use on the hard-to-access screws on our old head. This tool was invaluable. It is one with a small opening that takes different screw bits and holds them at a right angle to the short handle. I bought it at Ace Hardware. Trying to get a regular screwdriver on these muffler screws is almost impossible and it worked great for removing and replacing those four screws.

Many of the removal articles suggest removing the muffler from the aft cabin hole. So I did. It was a BEAST to do. When the old muffler is moved off its plywood pad and pulled amidships to the area behind the engine, the muffler ports stick up and barely clear the fiberglass lip of the cockpit sole down below. The wiring harness wires are even lower and are very difficult to reach to lift up to clear the ports. After the muffler comes past those obstructions, it is necessary to turn (yank!) it 90 degrees clockwise to get it to come far enough aft to get to the “hole” because of the way the hull is shaped compared to the underside of the aft cabin fiberglass. I strongly urge you to never even bother. If your ports are too long, you will never get it out that way and will waste a lot of time & energy. We learned just how easy it is to replace the new muffler through the head door, which we never bothered to remove. Take the old muffler out through the head door!!! When installing the new muffler have the ports face midships, tilt it in and down and then flat and back over the plywood base. It’s that easy.

The plywood bed of our old muffler was in fine shape, so we didn’t need to replace it as Ron Hill had done with his. While the alignment between the muffler inlet port and the riser/nipple section wasn’t spot on, we used the entire length of the new hump hose, which took up the slight bend. No cutting of the hump hose was necessary.

Exhaust Riser Removal Tips & Tricks: The hardest thing to do is get that bottom nut off the stud (even after soaking with PBBlaster; carefully mask the transmission to avoid any PBB getting on the seals). We had gone through this “bottom nut” difficulty in 2003 and again in 2008. I had given it a lot of thought and came up with this: While Morgan held a 9/16” box end wrench on the nut from below, I took a huge long one inch combo box/open end wrench from above and he held the open jaw of it on the end of the lower wrench while I hit it with a big hammer. Bingo! The nut came right off. Instead of trying to work that nut off from below, use two people and as much leverage as you can manage to work it off. Sockets and ratchets won’t work on that nut because of the configuration of the exhaust riser and the connection to the manifold. That long wrench & hammer worked, right away.

We purchased the new exhaust riser & insulation from Catalina Direct for $495. The insulation is sold separately from the riser, but CD won’t sell the riser without it. My records show the new riser with insulation was $165 in 2003. I didn’t price this from Catalina Yachts this time. The new separate insulation is installed with stainless steel metal straps that insert through pre-made slits in the insulation. It’s a nice arrangement and worked well. The CD Catalina 34 riser fit perfectly on our Mark I boat. Our 12 year old riser appeared to be in reasonable shape, but since “we were in there already” to replace the muffler, it made sense to do both. We reused the old flange, which is still in perfect condition.

Exhaust Riser Reinstallation Tips & Tricks: Using the vise and lining up the riser on the studs.

You need a vise to tighten the riser into the flange. We don’t have a vise, anywhere. My friend Rick has a woodworking shop in our marina, but his vise was too small. Rick suggested we use his friend’s work truck, which had a big vice hanging off the back! We had pre-measured and marked the position before applying the anti-seize and thread-sealing compound that comes with the CD riser package. To get it lined up properly required turning it 270 degrees more once the threads started getting a grip by hand. We returned to the boat, tried it out and had to return to the truck to make one small adjustment. We were glad his friend hadn’t driven off with his truck!

The previous replacement articles summarize the work: “Carefully line up the new riser with the studs on the engine while holding the hump hose end of the riser.” Because of the peculiar geometry of the flange, riser, hump hose and muffler, it is necessary to first get the hump hose installed on the riser and then also to get it started onto the muffler inlet port, while at the same time trying to line up the studs. Morgan had lined up the flange with the studs when he said it was “OK,” so I made the mistake of pushing down on the hump hose end, which then messed up the alignment. I should have suggested he push the flange onto the studs before I pushed down, so I had to go back down into the “hole” and push up on the entire assembly to loosen the hump hose end and we started all over again. Once he got the flange lined up again he pushed them onto the studs, and then he used the hammer and banged it home. The trick here is to get the flange lined up and ONTO the studs FIRST and leave the hump hose connected to the muffler but not too firmly in place. It really is a juggling act! Once the flange is most of the way on the studs, using a hammer won’t hurt because any damage to the threads on the studs will be underneath the flange body, leaving the ends of the stud threads in fine shape. We also used Rector’s Pipe Dope on the hump hose connections to the riser and muffler port.

Flange Gasket: We carefully cleaned both the end of the exhaust manifold and the flange. This is essential. We used a bit of high temperature RTV gasket material on the flange side of the gasket. This made it easier to deal with the gasket while we aligned the flange and the studs, since the gasket was stuck right on the flange with the RTV. Don’t be tempted to slather RTV on the manifold end. First, it isn’t necessary if the manifold is perfectly CLEAN, and second, it makes cleaning the manifold end much, much harder the next time, and there will be one.

Tightening the bottom nut back onto the stud: We simply reversed the big combo open/box wrench trick, making it very easy to get it tight.

Hoses: Removing the head water faucet hoses is necessary. We also replaced the raw water hoses from the strainer to the Oberdorfer raw water pump, from the pump to the heat exchanger, and from the HX to the vented loop and to the nipple. There is a slot in the fiberglass on the port side of the engine area for the hoses that is important to reuse. It keeps the hoses tight as they come around that corner under the head sink and keeps them clear of both the HX and the riser. Having the raw water hose off the strainer gave a little bit more room to get the new muffler in. We have our external regulator under the head sink and there’s still enough room to get a muffler in (and out).

Dollar Bill Test: Ron Hill’s excellent advice to assure clearance between the top of the heat exchanger and the bottom of the riser was checked out. In fact, because of the new insulation material from the CD kit there is even better clearance now than before. This is always critical to check.

Other Items: We, of course, removed the HX to do the riser work, and cleaned and painted it while it was out. For years, I’d struggled to get the hose clamp on the port side tightened once the HX was put back in place. This time, I left that long 7/8” hose connected to the HX and disconnected it at the copper elbow underneath the alternator. This is the copper elbow from the 1” to 7/8” black hose from the coolant pump, which is a Toyota hose that can be purchased from any auto parts store, instead of the pricey one from Universal. Do a search on “Toyota” on the Forum to find sources.
 
Jun 2, 2014
348
Catalina 30 mkII - 1987 Long Beach Shoreline Marina
So, the whole thing is going to cost around $500-$600 if I order replacements from CD.
 
Jun 2, 2014
348
Catalina 30 mkII - 1987 Long Beach Shoreline Marina
Thanks Stu. I am still going to attempt to get it out and see if it's gunked up, and if it doesn't look rotted and leaking, I'll try to re-use it.
 

DArcy

.
Feb 11, 2017
662
Islander Freeport 36 Ottawa
I was having issues on my C&C 27 I thought might be exhaust blockage so I took mine apart. It was slightly blocked but not all that bad. When I started to scrape it out, the screw driver went right through the wall of the mixing elbow :yikes:. That's why I did it right after haulout in the fall, I had time to get parts to build a new exhaust. I tried to find an off the shelf elbow but didn't have any luck so I built my own, the only thing I needed to buy specifically was the flange for the manifold. Mine worked out well with the help of a friend's machine shop but I suggest buying off the shelf if you can.
Before taking it apart I sprayed each bolt generously with Liquid Wrench about 6 times over 2 weeks. The bolts came out fairly easy after that (with an impact wrench).
 
Feb 26, 2004
20,918
Catalina 34 224 Maple Bay, BC, Canada
Thanks Stu. I am still going to attempt to get it out and see if it's gunked up, and if it doesn't look rotted and leaking, I'll try to re-use it.
The ONLY possible part to get "gunked up" is where the nipple meets the riser right above the muffler. That is RARELY the case with these exhaust risers, because the water is chugging through pretty quickly and keeping the nipple pipe clear.
The REAL failure is at the weld which is being constantly attacked by a mix of hot water and heavy duty exhaust gases. The pipe literally rots from the inside out. What you see visually, given the facts you stated in your OP, means the pipe is toast.
Besides that little factoid, one could say "that while you're in there" that amount of effort is part of the remove & replace saga, unless on your boat you can visually see that it's clear and has no internal disintegration without taking a lot of stuff apart. Hard to tell without a boroscope.
Look, I've done this three times on my boat (four - one was a removal and reinstall on the flange only job). My first was when the riser broke filling the cabin with brown soot.
Happened to Les Troyer just last year.
The other two for me was preventative maintenance.
Another friend had exactly your symptoms, and we told him to not set out. He did, and it failed halfway home from outside the Golden Gate Bridge!
I strongly urge you to reconsider the "short way out." Do it right since you described what may of us have seen, personally, as imminent failure.
Good luck.
 

DArcy

.
Feb 11, 2017
662
Islander Freeport 36 Ottawa
Here is what mine looked like when I took it off, it was wrapped in insulation which masked the condition. It was obviously overdue to be replaced.
20170224_101721.jpg

And the new one I built
20170522_110244.jpg

I did wrap it with exhaust insulation after installing.
 
Jun 2, 2014
348
Catalina 30 mkII - 1987 Long Beach Shoreline Marina
The ONLY possible part to get "gunked up" is where the nipple meets the riser right above the muffler.....I strongly urge you to reconsider the "short way out." Do it right since you described what may of us have seen, personally, as imminent failure.
Thanks Stu,
I don't know what I'm getting into yet, so one step at a time I guess. First thing is to get it off and look at it. That will take me a couple of weeks, I'm going out of town the rest of this week, and I'll get help the week I decide to crack it open. I'll take my time and either make sure it's good and put it back, or I'll replace it. Gotta get it out first though.
 
Feb 26, 2004
20,918
Catalina 34 224 Maple Bay, BC, Canada
I'll take my time and either make sure it's good and put it back, or I'll replace it. Gotta get it out first though.
To :deadhorse:or perhaps I wasn't clear enough: If you get it out, and you've gone to all that effort, why replace, say, a half used up component and put it back on when you could put a brand new one in and get twice the life out of all that work! :)

If you just are able to inspect it carefully, without removal, then go for it. I simply doubt from your OP that it isn't compromised.

Good luck. Please report back, preferable on this very thread. Have good trip.
*************************
Re: antifreeze. Yes, you need to drain your coolant. It is because of how the engine is built. Here's how:

Engine Overheating 101 - How to Burp Your Engine (Reply #6) Engine overheating problem (with Instructions "How To Burp!")

You can also reread my long post abpv, re the gasket for the flange to the manifold.
 
May 20, 2016
2,890
Catalina 36 MK1 94 Everett, WA
Why would there be antifreeze in the exhaust system? That doesn’t make sense to me.
The exhaust manifold doubles as a coolant tank. The gasket and exhaust adapter keep the coolant in the tank and the exhaust separate.