From: RWolf99@aol.com
Message-ID: <0.897b447a.2545c0bf@aol.com>
Date: Mon, 25 Oct 1999 10:18:39 EDT
Subject: How NOT to install a capacitance fuel probe
To: lancair.list@olsusa.com
Mime-Version: 1.0

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I almost had a disaster installing a capacitance fuel probe in my header 
tank.  This post is to tell you to avoid the problem, and hopefully to find 
out how to do it right.  (I have to install two more...)

The basic task was to cut a hole in the tank big enough for the body of the 
probe to fit thru, then glue on an aluminum backing plate (the one with the 
five holes) onto the inside wall of the tank.  

I used a 2-5/8" hole saw to cut the hole.  It worked great.  The probe body 
(one of those Skysports probes) fit quite nicely into the hole.  Not snug, 
but not loose and sloppy, either.  I realized that there was very little 
margin for the backing plate to be off-center.  What better centering device 
than the probe itself?  So I covered the probe with release tape ("Flash 
Tape" from Aircraft Spruce is what I use and it normally works well) and 
bolted the probe to the plate.  I did a trial fit of the probe by inserting 
this assembly into the hole from the inside, snaking the wires thru the hole 
first, then the probe body, then the backing plate -- which of course, did 
not fit thru the hole.

Then I mixed up some epoxy-flox and applied it to the backing plate.  I 
brushed a light coat of pure epoxy (no flox) onto the 
cleaned-then-scuffed-then-cleaned inner tank wall to ensure that there would 
be no leak paths between the backing plate and the tank wall.  I reinserted 
the probe-and-plate until the plate fit up against the tank wall and the 
excess flox squished out.  I then hung a 5 pound weight from the probe body, 
attached via the safety wire holes in the bolts holding the probe to the 
plate.  I scraped off the squished out excess flox from the tank inner 
surface with a tongue depressor and applied peel-ply over the residue.

So far, so good.

Imagine my surprise when, a few hours later, I tried to pull the probe off of 
the plate and failed!  Yes, I had removed the bolts.  But there was enough 
epoxy gluing the flash tape to the backing plate and holes edges that it was 
EXTREMELY hard to remove.  I finally managed to pry the probe off with my 
fingers, but it was a very near thing.  I don't want to do this again on my 
wing tank fuel probes.

Any ideas?

Oh, yes.  The next day I put 3-BID over the plate to complete the job.

- Rob Wolf
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