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Old 07-13-2022, 02:38 PM
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edwardc edwardc is offline
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Exhaust leak

Appologies in advance for the long (but hopefully not rambling) post.

11 years ago, I built a new exhaust hot-section out of 316 Stainless pipe. I spent the extra on stainless so I would hopefully never have to do this again. (https://www.moyermarineforum.com/for...php?albumid=73) Everything except the MMI flange and MMI injection point was SS.

About a month ago, while motoring to a club rendezvous, we left a cabinet door open that connects directly to the engine compartment. An hour later, the Carbon Monoxide alarm went off in the cabin, even though I run the blower whenever the engine is on. Fortunately, we were outside in the cockpit. I closed the cabinet, ventilated the cabin, and finished the trip.

Once back in our home slip, I started to look for the leak. I could definitely smell exhaust in the engine compartment, but was unable to immediately locate the leak without burning myself, and I didn't want to spend much time with my head in there with the CO while the engine was running.

So my next thought was to use an infra-red thermal camera to locate the leak. There are numerous cheap ones available, but I soon discovered that their resolution is a joke (~60 x 60), and usable ones are in the $300 - $400 range. Too much for my budget!

My next approach was to buy a fast-responding digital CO meter. I thought I could probe around with it while the engine was running and look for a spot where it jumped up. The meter showed that, with the cabinet closed and the blower running, the cabin level was zero. The problem came when I brought the meter into the engine compartment. It instantly shot up to over 200 ppm (!) and started sounding an alarm that meant "Get Out Now!"

At this point, I was stumped, so I talked to my mechanic brother who said "Why don't you smoke test it?" He then described a technique that uses a small smoke generator to pump smoke into the exhaust system with the engine off. This way, there is no danger, no heat, and a strong flashlight will reveal the leak easily.

There are numerous plans all over the Internet for building a homebrew smoke generator, but I took the easy way and ordered an inexpensive one from Amazon.

And since I had long ago followed Hanley's lead and installed an oxygen sensor in the manifold close-off plate to run a Fuel:Air Ratio gauge, removing the oxygen sensor provided a perfect place to inject the smoke.

And it worked! I found THREE streams of smoke coming from somewhere on the underside of the MMI exhaust flange, just out of sight. By touch I dislodged large flakes and chunks of rust from the flange (its AMAZING how much rust a little bit of mild steel can make!), and found the SS bolts to be in perfect shape. But this is where my luck ended.

I have spent weeks trying to get those bolts out. The upper one is particularly difficult, as the first elbow blocks access with a socket wrench, and I can only get to it with a box end wrench. I soaked it in Kroil. Tapped on it. Soaked it some more. Tapped some more. Tapped on the wrench with a small hammer. Applied heat to the flange and manifold with an electric heat gun. Upped the ante to a micro butane torch. And when that failed, rearranged hoses and wiring out of the way as best I could and applied a plumbers MAAP torch! Still no joy. At least I didn't set the boat on fire.

I transferred my attention to the lower bolt, which could be accessed with a socket wrench. Applied lots of Kroil, and successively tried a 12" ratchet handle, an 18" breaker bar, and finally managed to get a Ryobi electric impact driver in there and cranked on it until the 6-point socket was getting hot from just the impacts! Never budged. I tried this repeatedly, alternating with Kroil until my shoulder gave out.

And that's where I am today. Access is really difficult. I either have to squeeze in over top of the engine, or reach down and in from one of the cockpit lockers. I managed to get my phone in there and snap some pictures, and was astounded to find that the MMI flange has completely cracked through (!), right next to the boss for backpressure testing. This expansion is probably pinning the bolts in place.

So I'm open to suggestions. The SS pipes are in perfect condition, so I really don't want to hacksaw them off. In the past, working on car exhausts, the answer has always been "More Heat!", but my only option for that is an Oxy/Actelyne torch!!

At this rate, I'm going to lose the rest of the season!
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1977 Pearson P-323 "Dolce Vita"
with rebuilt Atomic-4

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