Difference between revisions of "Engine zincs replace 2007"

Revision as of 21:45, 30 January 2008

There are two pencil zincs on Nevermore's engine. Both are shown in the Westerbeke engine Parts List "Cooling System" figure on page 220 (and repeated on page 222.) This figure is also on the [web], as is the parts item list that is on our hardcopy pages 221 and 223.

The heat exchanger is REF number 23 (P/N 15799), and the oil cooler is REF #32 (P/N 11518).

Both pencil zincs are shown as REF #33 (P/N 11885). This is a workable part for the heat exchanger, but not for the oil cooler, which requires a fatter and possibly shorter pencil, with a larger screw thread radius.

PHOTO DESCRIPTIONS

A: Old pencil zinc removed from the heat exchanger (the heat exchanger moves sea water over cooling tubes which have circulating fresh water, which in turn cools the engine.)

The little chunk was found inside the heat exchanger, along with several very small (like sand) pieces of zinc (and/or possibly actual sand?)

B: New pencil zinc installed Fall '07; we found two of these aboard Nevermore in the box of new spare parts.

C: Old pencil zinc removed from the oil cooler (the oil cooler moves sea water over cooling tubes which have circulating engine oil, the same oil used to lubricate and cool the engine.)

D: Old pencil zinc found aboard Nevermore; it's the same size as (B), so we assume it was removed by previous owner, but at unknown (to us) time.

E: New pencil zinc we bought, ready to be installed in the oil cooler (Jan08); we had to cut down its length (we discuss this below, but note that its original zinc part is longer than the heat exchanger zinc, whereas the oil cooler is smaller diameter than the heat exchanger.)

F: Another new pencil zinc for the heat exchanger, presented here to show the different size of item E zinc. We bought it (West Marine) to compare to the units we found aboard (see item B.)

COMMENTS and THOUGHTS

• Glossary: (quick-'n'-dirty definitions for tech-newbies interested in the Nevermore fitting-out saga):
  • HE or Heat Exchanger : raw seawater is pumped through an outer cylinder at the same time that fresh engine cooling water is circulated through pipes in the cylinder; heat is transferred from the fresh water to the seawater and removed from the engine.
  • OC or Oil Cooler : raw seawater is pumped through an outer cylinder (the same water the HE uses), and cools the engine oil which is circulated -- probably via small pipes -- inside the cylinder; the engine oil is cooled.
  • zinc, or pencil-zinc : well, start by looking at the pictures B, E and F; consists of a bronze (?) threaded plug and a pencil of zinc which (often) screws into it; when electric currents flow in the salt water in which the pencil is emmersed, the zinc, being the least-noble metal we expect to find around the boat, will become a sacrificial anode, and it, rather than other boat parts, will be eaten away by galvanic corrosion.

1. The HE and OC are shown in the "Cooling System" diagram in the engine's Parts List, on page 220 (and repeated on page 222.)
   1. The HE is REF #23 (P/N 15799) and the OC is REF #32 (P/N 11518). The parts list shows both using pencil zinc REF #33 (P/N 11885) but we see that this part only fits the HE.
2. Two pencil-zincs for the HE like Picture B were found aboard; one replaced the Pic A zinc in Fall '07.
   1. The Pic B zinc is very similar to West Marine's unit. They have 1/4" NPT thread plugs and a 3/8" diameter x 1-3/4" length pencil.
   2. We don't know whether the Picture B unit is the correct one. We'll discuss later that maybe we want a longer pencil.
3. The OC's zinc Pic C, removed from the OC in Fall '07, had no replacement aboard. And the Parts List misidentifies the Westerbeke P/N for it.
   1. The plug threads and pencil diameter of West Marine's zinc, Pic E (before we cut it shorter), match the Pic C unit and replaced the old Pic C unit.
   2. The Pic E zinc's plug has 3/8" NPT threads, and the pencil is 1/2" diameter x 2" length.
   3. With the uncut pencil, we screwed the plug in 3-1/2 turns. We think, but are not sure, that the pencil started bottoming out (the O.D. of the OC's cylinder is about 2-1/8", but there's a built-up female threaded piece about 9/16" extending radially off the cylinder. Looking in the screw hole, we maybe saw some "radiator core" material that the pencil might be hitting (or else it could just be chips of zinc?) The net "theoretical" clearance needed would demand cutting about 1/8 to 1/4" off the zinc, but we cut about 3/8" off (as you can see from the Pic E "cookie" shown with the unit.
   4. We note that the length of the OC's zinc is more critical than the HE's, because the OC zinc screws in downward from the top of the cylinder. Hence, if the water doesn't fill the OC cylinder, the whole zinc won't be innundated. (But probably our mental image of the water kind of burbling through the OC cylinder, rather than filling it completely, is inspired by the way that seawater burbles out the exhaust port.) At least when the engine isn't running, the water level quite probably DOES drop.
4. We've tried to make some sense of the shapes of the corroded pencils of Pics A, C and D.
   1. The HE's zinc gets screwed in from the underside of the cylinder.
      1. Pic A's zinc has rotted near the bottom of the cylinder.
      2. Thom thinks the little pointed piece of zinc, found lying on the bottom of the HE cylinder, should be pictured with its pointy end pointing to the left toward the plug (i.e., pointing down in the HE.) In which case, the water that brought the currents to the zinc would not inundate the zinc part for long periods of time.
      3. Mentally putting the chunk (rotated 180-degrees) back on Pic A's plug, the end of the zinc away from the plugs in Pics A and D would be approximately the same length. So we can say that some water condition consistently corroded the ENDS of the two plugs. Thom can't imagine it being anything other than the flow of raw water pumped through the HE and OC hitting that end of the zincs. And then the zinc that came to us installed in the HE might have had the little piece eaten off with a shallow pool of water that stayed that way while the boat wasn't used in the months (years(?)) before she came to Boston. And that the Pic D zinc was itself left in too long, but during a time of meaningful usage of the engine, where it lost its end away from the plug.
5. Questions/mullings:
   1. I'll bet the little hole visible in Pic D, which is drilled maybe 1/32 to 1/16" into the pencil, provides a gauge of when the zinc should be replaced, assuming of course that it hasn't lost any length.
   2. Thom has never seen a writeup on how to "check and replace zincs". Specifically, should be use thread tape or goop on the new zincs, since all landsman's directions for NPT connections talk about doing so. But of course, we homemakers usually see this info when doing water or gas work...
6. Research TODOs:
   1. Order an "official" Westerbeke HE zinc, to see what size it is.
   2. Ask Westerbeke what length the OC zinc should be (see our "want longest possible" note above.)
   3. Get a good eye to see what's at the bottom of the OC cylinder.
   4. Flush, or reverse flush, the HE and OC (probably separately) (one winterizing source says to do this to the HE).