Modifications to Osco center riser exhaust manifolds (s/b ford)

Discussion in 'Gas Engines' started by missinginaction, Apr 17, 2012.

  1. missinginaction
    Joined: Aug 2007
    Posts: 1,081
    Likes: 240, Points: 63, Legacy Rep: 512
    Location: New York

    missinginaction Senior Member

    Hi Folks,

    I'm usually in the wooden boat forum but I have a question here for you engine guys.

    I'm restoring a 1973 Silverton and am replacing the exhaust manifolds on a 302 Ford as part of the work. The old manifolds were log style so a direct replacement was not available. The Osco center risers will fit nicely and I've pared them with a couple of Centrek Vernatone MK II mufflers. Before I install this gear I have a couple of mods in mind. I called Osco and spoke to a very nice man but he informed me that the people that used to handle "the more technical" questions don't work there anymore. Geez, I guess this is the new economy. So for what it's worth, here are my questions.

    The cooling water runs from the seacock through a v-drive, up to the bottom of the exhaust manifold, it enters the manifold and is pushed up through the riser and then out the back where it mixes with exhaust gas and exits the boat. There are two 3/4" NPT threaded ports at either end of the manifold (the idea is that to run water through one and simply plug the unused port).

    I'd like to add a zinc to the unused port to help manage corrosion inside the manifold passages. The zinc would look like this.....

    I don't have 3" inside the manifold, so I'd have to cut the zinc pencil back to about 2" to fit.

    I'd also like to be able to drain the manifolds at the end of the season. I'm wondering if anyone has drilled and tapped a manifold similar to this to accept a petcock. I can see the exhaust passages and have a nice spot between the center ports where a drain would fit nicely. It would seem that mounting the manifold on a drill press and carefully drilling the outside of the water jacket would do the trick.

    Any thoughts on these modifications would be appreciated.


  2. kenJ
    Joined: Jul 2005
    Posts: 349
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    Location: Williamsburg, VA

    kenJ Senior Member

    Can you drain the manifold by removing the zinc? That would be easier than maintaining a petcock. No problem with cutting down the pencil zinc, I have to do it to fit my heat exchanger. One problem with using the pencil zinc, quite often they break. You will need a way to clean out the manifold or eventually the water passages may get blocked by broken bits.
  3. missinginaction
    Joined: Aug 2007
    Posts: 1,081
    Likes: 240, Points: 63, Legacy Rep: 512
    Location: New York

    missinginaction Senior Member

    Thanks Ken. It occurred to me to that I could pull the zincs to drain the manifolds. I'll keep an eye on the zincs for fractures.

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