Exhaust Riser Replacement
This is for an M25, from my Feb. 2004 Mainsheet article, (pictures extra - haven't figured them out yet for here) (Psst- become an association member and get the Mainsheet - lots of great information in every quarterly issue)[sorry about the justification - that's cut & paste for ya...]********************************On Saturday, August 16, 2003, I had just completed an early sail across theeastern end of San Francisco Bay, and had sailed south of the Bay Bridgetowards Pac Bell Park and a Giants baseball game. The wind died south of thebridge, so I was motor sailing with the engine at idle speed. I smelled dieselexhaust and looked around for a motorboat or ferryboat that had passed byupwind. There was none. But there was a huge brown black mass of exhaustcoming at me from the cabin! I immediately cut the engine, set the sails and theautopilot to head upwind in the very light air, and went below to open up all thehatches and ports.Inspection confirmed my initial idea that the exhaust riser had separated, rightabove the water injection nipple. Of course, I’d been “meaning” to make this areplacement for this year, but failure caught up to me first.A year or so ago Dave Davis had sent me copies of the exhaust riser drawingshe had received from Catalina Yachts. One showed the old five piece black ironassembly, and the other showed the new improved stainless steel model.I called Catalina, and they fabricated the new exhaust riser for me and I had it inhand within two weeks ($165). In the meantime, I had done research onobtaining professional help, and engaged Glenn Barton of Stone Boat Yard inAlameda to do the work.Since there has been much written about exhaust riser replacement on the websiteand in the message board, I won’t bother repeating that information.However, I noticed that no one had provided any pictures, so here they are: 1. Old riser and hump hose - You can see the nipple on the old blue hump hose, and the clean break in the black iron where the insulation begins. 2. New Riser - It came pre-insulated from the factory. Note the nipple on the port side that goes in under the head sink, the horizontal part that goes from under the sink to the engine compartment, and the drop and elbow into the back of the exhaust manifold, all one piece. The existing exhaust flange came off the back of the engine manifold easily, no doubt helped by the fact that I’d soaked the three studs with liquid wrench for three days before we did the work. The exhaust flange threads on to the threaded end of the riser. We used muffler paste on these threads. 3. New Heat Exchanger - I replaced the old 2 inch heat exchanger with the new three inch model that I bought last year. Glenn took the old bracket to his shop, and simply bent it down to fit the new heat exchanger underneath the new exhaust riser. 4. Connection underneath head sink - Glenn recommended a longer hose between the exhaust riser and the Aqualift muffler, instead of reusing the hump hose. Instead of the hump hose from the nipple end to the muffler, there is a large loop of 1 5/8 inch exhaust hose. This should cut down on the vibration between the end of the riser and the lip of the muffler. We used non-hardening pipe dope on the lip before clamping the hose to it.The work took about 6 hours. We also replaced all the water hoses and installednew clamps and a new antisiphon valve. The engine is running cooler than itsusual 180, down to 160 at all speeds.I had 1390 engine hours when the old riser failed. I believe that the riser was theoriginal one, since the previous owner had left me with very good records whichdid not indicate that he’d ever replaced the riser.I recommend that you all check your older exhaust risers. It’s easier to replacebefore failure. It took me over four hours to sail back to my slip the day of the“event” against a flood.Stu Jackson#224 1986 “Aquavite”