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Old 04-01-2018, 07:05 AM   #1
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Zincs unscrewing from plug

Hello Trawler friends!

This week is “Clean Heat Exchanger Week”. I have 5 heat exchangers on my Yanmar 6LP-STE. Air, Lube Oil, Transmission Fluid, Fuel, and Fresh Water cooler. Each one has at least one pencil zinc installed. I took off all end caps last year, cleaned the heat exchangers and replaced all zincs. This year I decided I was going to clean them again. In the process, I noticed that several of the zincs had unscrewed from the plug (As I had also noticed last year), and the zinc was just laying on the bottom of the heat exchanger.

I know for a fact a pencil zinc will break if it is over torqued in the plug.

So now my questions:

-Is this common?
-Can I buy pencil zincs that are not screwed in but are somehow permanently secured to the plug?
-What can I do to prevent this? Thread lock?

Thank you.

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Old 04-01-2018, 08:05 AM   #2
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I suspect that you are not tightening the zinc in the plug sufficiently. Grab the zinc with pliers and use a wrench on the plug. It is sort of a trial and error situation to get it tight enough to not fall off but not so tight that the zinc will shear off when you try to remove a partially wasted zinc. Lubing the threads will help- grease, lanocote, etc.

Some have recommended Locktite but that just makes removal that much more difficult.

If the zinc shears off, you can drill it out partially and then use a tap to clear the threads. Or drill it and put it in a jar of Barnacle Buster or equivalent to dissolve the remaining zinc. Or replace the plug. I have done all three.

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Old 04-01-2018, 08:07 AM   #3
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Heather I would think you are more likely to strip the threads on a zinc anode before it shears but I've always just tightened them with a pair of multigrips or vicegrips on the anode part and never had one unscrew. You could try a thread lock but it will make it harder to change and may cause some electrical isolation of the two parts.
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Old 04-01-2018, 08:14 AM   #4
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Good point about the electrical isolation. Yesterday I used vice grips and a socket wrench to remove the plug from the zincs since I am only installing the plugs to circulate barnacle buster to the system. Once I circulate barnacle buster to the system, then I will remove the plugs and insert the zinc. But yes, it is definitely possible that I did not tighten the zincs down before installed them last year. That’s probably what it was.
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Old 04-01-2018, 08:18 AM   #5
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I always messed up the zinc's threads a bit with pliers so that they were a little more difficult to screw or unscrew.
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Old 04-01-2018, 09:14 AM   #6
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You can buy those caps too, they are cheap so if you have difficulty getting an old zinc out, just pitch the whole thing.
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Old 04-01-2018, 09:34 AM   #7
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I have several end caps with broken zinc ends in them that I would love to get out. The stub ends are very irregular and I think getting a drill started will be an issue, but I haven't tried. I have wondered if there is some bath I can put them in to dissolve it the remaining zinc. Barnacle buster is an interesting idea, but of course I have none. And I would pitch and buy new caps, but am in Mexico, not the Land of Plenty. So I keep stuffing them back in the box to be dealt with another day.

Does anyone know if vinegar would work?
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Old 04-01-2018, 09:47 AM   #8
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Zincs unscrewing from plug

Vinegar is too slow for this I think. You would be waiting for like a week. Incidentally, the worst problem I have with cleaning surface corrosion off metal items with vinegar is a soak that I expect to last a couple days that I forget between weekends and it sits for one or two weeks. I once soaked an old penn yan badge inadvertently for a month. There was little left.

I also have a permanent stain in my stainless sink from quick soaking a zinc plug cap I could not find with something too strong, but I wanted immediate gratification. Now I keep an organizer with a collection of pencil zincs and their bolt heads so I’m not tempted to do silly things. As noted, they are cheap. Just buy more than you need right now.
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Old 04-01-2018, 09:58 AM   #9
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When you loosen the brass plug, before you unthread it all the way, wiggle it vigorously side to side. Breaks free some of the corrosion on the anode and then it is more likely to come out of the hole attached to the plug.
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Old 04-01-2018, 09:59 AM   #10
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pool acid (muriatic) will dissolve the remaining zinc in the plug. But pipe threads are designed to distort when used so reusing the plug may result in some dripping.

I always used some rector seal on the threads anyway. Check continuity with a OHM meter is worried about contact .
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Old 04-01-2018, 10:01 AM   #11
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To get a stuc anode out if the plug comes free use am ALLTHREAD nut. HD and lowes have them.
The nut will fit into the hole and screw onto the zinc threads so you can pull it out/
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Old 04-01-2018, 10:18 AM   #12
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Quote:
Originally Posted by twistedtree View Post
I have several end caps with broken zinc ends in them that I would love to get out. The stub ends are very irregular and I think getting a drill started will be an issue, but I haven't tried. I have wondered if there is some bath I can put them in to dissolve it the remaining zinc. Barnacle buster is an interesting idea, but of course I have none. And I would pitch and buy new caps, but am in Mexico, not the Land of Plenty. So I keep stuffing them back in the box to be dealt with another day.

Does anyone know if vinegar would work?
Take the plug to a belt sander, anything sticking up will be flattened. Then take a dreamer tool with a ball carbide bit to it. Once you have a depression a drill bit will do the rest. A left handed drill bit works magic.
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Old 04-01-2018, 12:37 PM   #13
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I do (or did) have a supply of extra caps, but over time the pile of new caps has gotten smaller, and the pile with stuck zinc ends has gotten bigger.

Of course they are broken off down below the top edge of the cap, so sanding down won't flatten out the surface for drilling. I could go at it with a dremal - that's an option.
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Old 04-01-2018, 01:03 PM   #14
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My notes on this indicate I've done it by drilling and digging (awl or something similar).

I also made a note to myself NOT to use heat in the process. IIRC something about generating and breathing ZnO.
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Old 04-01-2018, 01:07 PM   #15
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Greetings,
Mr. tt. I think Mr. b gave you the answer in Post #10. Muriatic (Hydrochloric) Acid. There's also a possibility that a Mexican resort with pool facilities may have muriatic acid on hand. (probably 4-6 oz will do maybe 15 caps). What may help things along is drilling a hole in the center of the stub. It needn't be all that large, just provide an acid channel to the blind end of the stub. Monitor closely. Depending on the porosity of the remaining stub the reaction could be fast or slow. Do this outside and wear safety equipment.

Please double check on my advice regarding the proper acid. My memory is getting so poor it's beginning to frighten me.
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Old 04-01-2018, 01:12 PM   #16
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Please double check on my advice regarding the proper acid. My memory is getting so poor it's beginning to frighten me.

Being frightened is a sign you have no reason to worry. After all, you are only concerned because you [remember] the times you have forgotten something. If you never remembered forgetting you wouldn’t be concerned. So your concern is a sign functioning memory.

Uh... what was I saying....?
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Old 04-01-2018, 01:14 PM   #17
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You can put a band of nail polish around the zinc/cap interface but not the threads after screwing in the zinc. This will stop the zinc from breaking off at the threads.
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