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Old 08-10-2012, 12:38 PM   #1
Join Date: Apr 2011
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Smile HX Zinc Ford Lehman 120

Replaing pencil zinc anyone know the correct size for the zinc that screws into the capbolt.
And do I use any pipe dope or sealant on the capbolt to HX assembly?


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Old 08-10-2012, 01:09 PM   #2
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Two sizes will fit, a skinny one and a fat one that is almost the exact diameter of the hole. We usuall use the fat one. Take the cap to a marine store to get the proper size if you don't have the old zinc as a reference anymore.

Do not put anything on the threads. The zinc requires electrical continuity with the exchanger to do its job. The threads are tapered so the cap tightens up as you tighten it down. Don't overtighten it, just make sure it's a good snug fit. We have never had any leaking problem around ours.

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Old 08-10-2012, 02:07 PM   #3
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Thanks, Ironically the caplbolt was torqued very tight and appeared to have some pipe sealant on the thread. Maybe thats why there was no zinc left?

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Old 08-10-2012, 11:42 PM   #4
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The zinc is gone because it sacrifices itself protecting the heat exchanger, nothing to do with how tight the cap is or the use of sealer.

If after many hours the zinc were not partly consumed then you have a problem to correct. The zinc[s] must be consumed to protect.

You do need to check the zinc reduction rate often untill you figure out what the changeout interval will be. Do not just put in a new one and forget about it for too long. Changeout time is when about 1/2-2/3 is gone.

I do use a sealer on the threads of my engine zincs, not a Lehman, or there is leakage, really a slow weep leaving salt crystals, unless I wind it TIGHT which is a good way to jam it or damage the threads. Not much sealer is needed and the interference thread of the taper will cut through the sealer and make metal to metal contact allowing the zinc to do its job.
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Old 08-11-2012, 09:55 PM   #5
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I use spark plug anti-seize between the cap and zinc. It is a good conductor and keeps the zinc removable so I don't have to keep buying the brass caps.
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(NOT a trawler)
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