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Old 03-30-2019, 10:28 PM
BostonSailor BostonSailor is offline
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I replaced my hot pipe section.

I got a lot of advice from Don and Ken at Moyer Marine and these forums. I wanted to share my results.

I have a 1979 Pearson 30 with an Atomic-4. The cast iron mixer in the hot exhaust section was very corroded and eventually developed a crack. We noticed the crack because it set off the boat's CO2 detector. On close inspection, there was also a little bit of spray. It was time to replace it.

The Catalina-style exhaust section sold by Moyer was the wrong shape, so I made my own. I purchased the exhaust flange, the inline cooling water exhaust entry fitting, and the exhaust wrap kit. I got a 2-foot section of 1-5/8" marine exhaust hose from West Marine. Then I went to Home Depot and bought a variety of pipe pieces. All of it was 1-1/4" black steel. Black iron (aka black malleable iron) is also good, and it's ok to mix. Do NOT get any galvanized pipe. The zinc coating burns off and is quite toxic.

The assembled unit consisted of (in order):
- Exhaust flange
- 90 deg. elbow
- 10" nipple (straight pipe, threaded at both ends)
- 90 deg. elbow
- 90 deg. street elbow (one end male, the other female)
- Water/exhaust entry fitting

I put it all together and tightened it as best I could. I used a vice to hold things and some large "persuaders" to turn pieces. If I was unable to get a section to tighten all the way to the desired orientation, I backed it off to get the orientation right. I'm assuming that any tiny gaps in the threads will corrode and seal on their own.

Removing the old section. I cut the old hose from the mixer to the lift muffler. Then I undid the two nuts atop the studs that hold the flange to the manifold. The nuts came off easily, but the flange was corroded on tightly. I managed to get a screwdriver under the exposed side and tried working my way around, applying more leverage as the gap widened. But I could not get the back side free. This was a mistake. As I was lifting one side while the back was still stuck, I ended up bending the back stud and so ... well I needed a new plan.

I needed to remove the manifold, and that meant removing the carburetor. As daunting as that sounded, it was really not that hard. I ordered a replacement manifold gasket from Moyer. Removed the carb and removed the manifold/hot pipe assembly. Once free, I "double nutted" the tops of the studs and was able to take them out.

Removed the old manifold gasket and cleaned things up with a rag and mineral spirits. Put the new gasket in place and reattach the manifold. Then reattach the carburetor.

Attached the new hot pipe assembly temporarily in order to ensure that everything lined up correctly. I measured and cut the right length of exhaust hose (it's a straight section that leads straight down into the lift muffler.) Then removed then pipe and wrapped it with the fiberglass heat wrap. I put hose clamps on the hose (thinking ahead), slid the hose over the inlet in the lift muffler, slipped the pipe assembly down over the hose. Next, with the flange gasket in place, tightened the flange to the manifold. Install the plug in the place on the flange where you could install a back pressure gauge if you wanted one. Attach the sea water hose from the heat exchanger to the water inlet in the mixer. Position and tighten the various hose clamps.

Did all the other spring engine prep (plugs, etc) and started the engine. Only problem was that I didn't tighten the hose clamps enough. Water was leaking from the bottom of the exhaust hose. I went to town on them. Restart the engine, and all is well.

All in all it took around 6 hours total. Would clearly be faster the second time -- but let's hope there isn't a second time. But perhaps this will help you.

Eric Brown
"Taurus" Pearson 30
Winthrop, MA

1) The old hot pipe section. Mixer is rotted through.
2) Here's the newly assembled replacement.
3) All wrapped up and ready to go.
4) Installed and working. (Exhaust hose needs a second clamp at the top. It's coming!)
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Old 03-31-2019, 08:00 AM
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Marian Claire Marian Claire is offline
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Welcome to the forum and thanks for the informative and instructive post.
S/V Marian Claire
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Old 03-31-2019, 09:06 AM
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ndutton ndutton is offline
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Schedule 40 or schedule 80 pipe? Also, you'll be happier in the future if you use 3/8"-16 studs with hex nuts to mount the flange. Stainless set screws work really well in this application.
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others

Last edited by ndutton; 03-31-2019 at 10:43 AM.
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Old 03-31-2019, 08:47 PM
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Al Schober Al Schober is offline
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Well done!
If it had failed under way, you'd be facing 1) a tow job to a repair facility, and 2) the cost for repair.
Exhaust failed on my former Tartan 30 during the delivery trip - CT to Maine. Tow Boat wanted to take us to New Bedford, but I held out for Marion and new owners insurance paid the extra. Burr Bros did a quality (better than I would have done - new pipe all stainless) and fast repair (8 1/2 hrs), but pricey. But it was on the new owners plastic, so.. I figure we split the cost, as I picked up the full cost of provisioning the trip plus the rental car for getting me home.
Yeah, the New Bedford shop would probably have fixed it with a soup can and a couple of hose clamps and got us under way in an hour for less than $100 - and we probably would have made it to Marion..

Last edited by Al Schober; 03-31-2019 at 08:53 PM.
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exhaust, hot section

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