C&C 27 Association Forum

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Atomic 4 Exhaust Replacement

I am in need of replacing my '71 Mark 1's Atomic 4 exhast system. I am not sure what is involved or how bad it is, but I am anticpating the worst. Does anyone know what one can expect in regards to parts needed, labor and overall cost? I plan on buying parts from Moyer directly. Any input would be greatly appreciated.

Thanks,

Greg Reese

Billerina, Hull #33

Last edited by (2008-10-06 00:06:55)

windyday

Member

Re: Atomic 4 Exhaust Replacement

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Here's a long-winded answer from a rank amateur. It is wise to seek expert opinion.

I'm doing this with a '74 Mark II, and have been on the learning curve. Exhaust replacement doesn't seem difficult, especially if one knows the existing design worked well and just needs to replace parts.

I got the old system dismantled, which is the first step. Perhaps the most critical is unbolting the exhaust flange from the manifold. Be patient if the bolts are corroded, to avoid breaking them. Don has a nice thread about how to deal with broken exhaust flange bolts. I got the bolts out with Kroil, gentle wrench work and time. Clean off the old gasket carefully and order a new one.

Once that's done, it's a matter of getting the old dry/wet stack and other components out of the boat, which I found very easy. If the old stack is wrapped in asbestos, use precautions when working with it (avoid inhaling fibers).

Right now I am working on the design, to ensure the replacements (1) will not create excessive backpressure (pipes or hoses too narrow, too many sharp bends, runs too long), and (2) will prevent water from backing up from the waterlift muffler into the manifold, wrecking the aft valves. If you know your present design has been working well, then you're half way there. This boat is new to me, so I'm spending more time on this design phase.

Sounds like the dry stack can be made from black iron nipples and elbows found in plumbing stores. If the old flange is salvageable, it can be used. The flange Don Moyer sells through MMI has a port for checking back pressure. I think Don uses never seize to get the pipe fittings tight. I imagine the key is to get the angles right when tightening the fittings. He sells a high temp protective coating on the stack to delay corrosion, before wrapping it with appropriate insulation. Stacks can also be made of galvanized steel or stainless steel, but there are compromises with those materials too. Not sure about brass or bronze. No exhaust stack lasts forever.

Presumably you have a waterlift muffler. I'm not sure about the age or inside condition of the metal muffler that came with this boat, so I am thinking about replacing it with a GRP or stainless model. GRP mufflers seem to be popular on many sailboats our size, but I can't figure out how to get enough distance from the raw water injection port on the dry stack to the muffler, to ensure the exhaust gasses are cool enough when they hit the muffler inlet. One manufacturer of a popular GRP muffler says 2 feet, as I recall, but check that.

MMI sells a compact stainless muffler with top ports. SS mufflers are more tolerant to heat, but it would still be important to ensure the gasses are cooled sufficiently that the muffler does not get too hot. My Mark II has a wooden shelf off to the side of the aft end of the engine. The shelf has a hole cut in it. I get the impression that this may have been a standard waterlift muffler location on the Mark II? Anyway, it now occurs to me that design seems to offer built-in air insulation for a warm muffler.

The MMI SS muffler outlet port requires 2" ID hose, which means I would have to upgrade the transom throughull to handle the larger hose (current one is 1.5" ID). I should rebed that through hull anyway, and add a flap to prevent pooping waves from flushing into the muffler. The larger hose would lower back pressure, if that is an issue. His model also has a drain to allow removal of accumulated exhaust water for winterizing or to reduce water volume in the muffler during a hard start. Commonly available GRP waterlifts do not seem to have that drain feature.

Some objectives in fitting components together are to ensure heat from the dry stack doesn't damage surrounding surfaces, joints don't leak noxious gasses and liquids, and components are well supported to prevent racking loose while under way. I plan to double clamp proper exhaust hoses with SS T clamps, for example, and build a support bracket for the dry/wet stack.

Some references I found useful:

<a href="http://www.boatus.com/goodoldboat/Marine_exhaust.asp">http://www.boatus.com/goodoldboat/Marine_exhaust.asp</a>
<a href="http://www.yachtsurvey.com/exhaust_risers.htm">http://www.yachtsurvey.com/exhaust_risers.htm</a>
<a href="http://www.moyermarine.com/forums/showthread.php?t=2772">http://www.moyermarine.com/forums/showthread.php?t=2772</a>
<a href="http://www.moyermarine.com/forums/showthread.php?t=2317">http://www.moyermarine.com/forums/showthread.php?t=2317</a>
<a href="http://www.yanmarhelp.com/i_exhaust.htm">http://www.yanmarhelp.com/i_exhaust.htm</a> (diesel, but principles similar).

Update:
<a href="http://www.abycinc.org/committees/P-01.pdf">http://www.abycinc.org/committees/P-01.pdf</a>

I get the impression that the C&C 27 design is kinder to exhaust systems than many sailboats in this size range. The other factor in our favour is that the Atomic 4 is not a powerful engine, which cuts us a bit of slack. But Don Moyer wrote that backpressure problems are common in sailboat A4 installations, so I plan to check the pressure after I get the new exhaust in place.

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"New" 1974 C&C 27 Mk II undergoing refit

Last edited by (2008-10-12 21:39:13)

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1974 Mark II C&C 27