The engine is a fresh water cooled LM318. It has a 4" dia. Sen-Dure heat exchanger. Every year, when I replace the pencil zinc I have to grind it down because the zinc's I can buy hit one of the legs of the heat exchanger.
Here is what the stock pencil zincs look like from most marine supply places.
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Here is what it looks like after I grind it to fit
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Here is what it looks like installed (with the end cap of the heat exchanger removed. It's not that easy to see in the last photo, but the zinc hits that bottom leg of the heat exchanger. If you try to force it in, I think it's possible the zinc could snap off the brass plug and you might not even know it if the end cap wasn't removed from the heat exchanger.
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I posted a question about it over on the marine engine discussion forum. I'm pretty sure that others must have run into this too. It's a pain in the neck, but I stick the zinc in the chuck of my drill press and grind away material with a 60 grit abrasive. if I had a lathe I would turn it down. I'm probably removing about 1/3 of the zinc to get it to clear the bottom leg of the heat exchanger.
Tuesday night racing starts this week at Barrington Yacht Club. I'll be crewing on Glamorous Glenice with Ray and many from the old crew. I've been away from it for years and am looking forward to getting back to it.
Best,
Chuck
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