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Date: Wed, 04 Apr 2007 22:55:38 -0400
From: Chad Robinson <crj@lucubration.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Sealing soldered connections.
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Joe Ewen wrote:
> Epoxies are used often in the electronics industry for potting/sealing 
> electronic components (Example, some ignition modules.)  I do not know 
> for certain that there are no ill effects, but I have used 5 minute 
> epoxy in several instances with no apparent (at least short term) ill 
> effects. Perhaps someone else on the list has more knowledge on the 
> use of and or variations in the types of expoxies.
You can use epoxy but you have to be careful. The really strong ones, 
like composite layup resins (MGS, West, etc.) cure very hard and 
brittle, so they can develop sharp edges that can chafe wires. 5-min is 
much softer and more flexible but doesn't take heat as well.

I love the roofing caulk suggestion. Cheap, simple, about as 
weatherproof as you'll get. The silicone base should resist heat very 
well, so it should be suitable for engine compartment use (I'd only use 
epoxy in electronics elsewhere). I still worry about varieties though. A 
simple test is enough to tell you if you have an acetic-acid curing 
agent by the smell. If not, probably anything relatively flexible, 
silicone-based, and inexpensive is just fine. Shoo goo, caulk, whatever.

One recommendation. Just because it's sealed doesn't mean some air can't 
be trapped in there ahead of time. When connectors, not soldered joints, 
are involved, I always recommend a dielectric grease applied to the 
terminals before attaching the connector. It keeps air and moisture away 
from the contacts.

Regards,
Chad