T&T: set screws

[Larry N. Brown]

At the risk of disturbing the gentlemanly discussion of fecal material and its
proper handling and packaging,  please let me put an information request
before this august group. I believe I mentioned that a blown main engine raw
water impeller led me to open the heat exchanger in pursuit of small pieces of
shed rubber. Turns out that the blown impeller was fortuitous in that I
discovered that my zincs were in bad-- indeed almost non-existent-- repair.
Three most upstream, in the heat exchanger, were the worst; the ones in the
inter-cooler and oil cooler not so bad. I replaced them all. Back to that in a
minute. And by the way, if anyone would care to discuss why the upstream ones
suffered the worst erosion, I'd love to know.

I noticed a small bolt in the tranny cooler. Pulled it out and it appeared to
be bronze with the tip reddened by exposure to salt water and galvanic. At
first I thought it was a small zinc with the tip corroded off. Then I
determined it was just a drain plug. As I tightened it back in, the head
twisted off. Well, any way it's plugged for the time being. I subsequently
bought an easy out for when I get a replacement.

Now, I pulled the plug on the other engine and took it to Lowe's to determine
its size/thread. 10mm/1. Thought I'd buy a few spares in silicon bronze or
cupro nickle and then I looked a little more carefully at the bolt. The tip is
exactly flat, no curve, bo bevel, bo taper. Flat. There had been no
sealant/teflon tape on the bolt. I think the face of it sits on a boss in the
cooler and is sealed by the pressure. I damaged the bolt by trying to tighten
it down like a pipe plug, sealing the threads.

Does anyone on the list have some insight into this matter?

Oh, and I discovered my Yanmar engines use plain ole "Merican zincs. Camp. And
they can be "reloaded" for <$2/ zinc. Check with Boatzincs.com or ask me
offline.

Regards,

Larry and Teri
M/V Cigano, 47' Prairie Sundeck Cruiser
Lying: 64 Cypress Road
          Covington, LA