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.
