1969 Chris Craft Roamer 46 Refit: Servicing the Aftercoolers

The Cummins 6CTA engines in my Roamer are aftercooled turbo diesels. The aftercooler housing is cast aluminum, but the core is made of bronze. Since raw water runs through the core, these aftercoolers are notorious for the sort of corrosion problems you’d expect from dissimilar metals in saltwater. Making matters worse, Cummins apparently assembles the aftercoolers dry, with no grease, Tefgel, or anything else to lubricate the joint, isolate the metals, and make disassembly easy. These engines only have 400 hours on them, but they came from New York and ran in saltwater. There’s just a bit of the green verdigris around the lower aftercooler end cap, which is telling me it’s time for service. The diesel gurus at boatdiesel say the aftercoolers should be serviced every two years, and I’ll be following Tony Athens’ method.

Popped the top off the aftercooler

Aluminum + bronze + saltwater = a few minor problems

After I popped the top off the aftercooler, I found a bit of aluminum and copper oxide outside the o-ring seal. This tells me there was a slight leak at the o-ring. I’m glad I decided to tear into this.

Green powder = evidence of an o-ring leak on the bottom, too

Green powder = evidence of an o-ring leak on the bottom, too

Bad hardware choice

Bad hardware choice…add steel to the mix of metals

The hex bolts holding the ends on the aftercooler are standard sized. Unfortunately, that brings the edges of the hex heads so close to the bronze castings that a socket won’t fit. This isn’t a good scenario for an aftercooler that was leaking saltwater.

Bolts came out without snapping

Bolts came out without snapping

I need to order new galvanized shoulder bolts for when I reassemble this. And they’ll get slathered with Tefgel when this goes back together.

Salt plugs one tube

Salt plugs one tube

Salt cleaned up pretty good

Salt cleaned up pretty good

Light at the end of the tunnel?

Light at the end of the tunnel?

The core tubes are clear now, so water flow won’t be restricted anymore.

Second aftercooler has similar issues

Second aftercooler has similar issues with the o-ring on the top end

Cleans up pretty good though.

Cleans up pretty good though.

The water side of the aftercooler cleaned up pretty well, but the air side is still a question. Because the bronze cores were installed dry into the aluminum housings, I couldn’t convince them to come out. So I brought both aftercoolers down to the house, stood them up on end, and poured some automatic transmission fluid into the air side. Two days later, ATF started dripping out of one and a week later it started dripping out of the other. I flipped the housings over and repeated the process. Finally, after two weeks, some heat from a MAPP torch, and occasional encouragement from a 3# sledge hammer tapping on a block of wood laying across the top of the core, first one then the other core came out.

The core is not too bad

The core is not too bad

Needs a good soaking and clean up

Needs a good soaking and clean up

Fortunately, the fins all look good and the corrosion on the ends was minor.

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Sloppy solder work in one spot, but that shouldn’t affect the aftercooler

I’m soaking both cores in degreaser now and will clean them up over the weekend, then I’ll reassemble next week. In the meantime, the window shop finally sent replacement trim rings for my helm station windshield. Adding to the potential drama, a blizzard is forecast for the area tomorrow and Saturday, with 50mph gusts and no less than 12″ of snow predicted. We’ll see how Tent Model XXX holds up.

Next up in our 1969 Chris Craft Roamer 46 Refit: Mid-Atlantic Blizzard 2016

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3 comments on “1969 Chris Craft Roamer 46 Refit: Servicing the Aftercoolers

  1. victor says:

    Looks nice and clean, I use a 22 cal rifle bore cleaning brush to push thru the holes and clean mine up,

  2. alloyed2sea says:

    Some kinda marine engineering there by Cummins – only the jokers at Mid-River Marina (North Tonawanda, NY) did worse when they installed the bronze seacock on my Roamer. This, the main water inlet for the aircon system, nearly sank the boat when attached to the a-l-u-m-i-n-u-m intake pipe. The pipe almost completely corroded away before a bad dream (the boat is sinking again) made me check it – only to have the connection fall apart in my hands. Managed to jam a wooden plug into to it and stem the tide, but needless to say an object lesson in the “magic” of dissimilar metals.
    Marelon!

    • victor says:

      I’ gotta ask, do you mean maleron seackock? What about installing a properly rated hose between the dissimilar metal piping?

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