Repairing leaking fuel tanks <after> removing top skin
Posted: Fri Feb 17, 2012 10:42 pm
Brian I laid it out for you back in November. I have copied and pasted my
reply from November below and I have also CC'd to the list as others
are/will be in the same boat.
If you go to bare aluminum "outboard" on each side of all filleted seams,
like I describe, the worry of bonding to old Proseal (or even sloshing
compound) is irrelivent although YES I do scrub the old proseal lightly as
well with scotchbrite to get the Proseal to hold to everything. The main
thing is to get fresh "membrane" of Proseal from bare aluminum to bare
aluminum across all the old fillets and where you come up the corners
(between the ribs and rear bulheads) from bare aluminum to bare aluminum on
each part and also the underside of the bulkhead flanges. Build it up in the
open corners between the rib and the bulkhead flange so that the Proseal
sits proud at all corners and goes onto the top of the flanges and ribs.
Then when it has harderned somewhat use an exacto knife to trim JUST ABOVE
the bulkhead/rib flanges feathering to bare aluminum about 1/2" to 1" in on
the flange. This way you'll have a skim of proseal that is bonded to the top
of the flange and a solid platform for the proseal to squeeze against in the
area between the rib and bulkhead flange when you put the top skin down, so
there will be no pin holes or leakage from the rear bulkhead. You should
also need to take a drill bit to clean out the first hole or two on each
bulkhead flange for the rivets before putting down the top skin, as it will
be filled in with Proseal if you did the corner filling sufficiently. These
bulkhead corners are the most common leakage area due to guys/gals trying to
put the top skin down and fill these areas in one process. It is very
important to have a cured (to semi-cured) "bath tub" created before putting
down the top skin. I go as far as letting the tank cure long enough before
installing the top skin that I can fill it with 100LL to the brim by tipping
the wing nose down to get as much fuel in as I can and letting it sit for a
few hours to watch for leaching or leaking (Water just doesn't work due to
it's surface tension). When you do this make sure all the lights are turned
on in the shop before starting (don't want no sparkies!!) or do it outside.
Wayne
............................................................................
............
Go to town with scotchbrite etc to get a clean bare
strip of aluminum completely around the tanks
perimeter/corners/stringers/top and underside of the rear tank bulkhead
flanges etc. You don't have to remove what's there, just
clean to bare aluminum along the sides of all existing fillets. This is what
I did with the Rebel that went to Maui. Then you can reproseal all seams,
give the rivets a coat and know that they are binding into the clean alum
surface to form a seal. Be sure to build a smooth lid seal at all the
bulkhead and rib junctions and let it cure before putting the lid skin back
on the tank. I also fill the tank with fuel while it's still open to make
sure it indeed is leak free in the "bath tub" configuration. Then I let it
air dry for a few days before I proseal down the lid.
Brian, With you leaving the .020 skin on through the tank you are basically
sealing
to it and the .040 skin is just reinforcement for the tank. As long as you
get the ribs/bulkheads sealed to the .020 you should be alright but it's
more important for you to have a seal around EVERY rivet otherwise your fuel
can run between the two skins and make it impossible for you to find where
it is really coming from. Anyone else would just have a dripping rivet that
can easily be fixed by undercutting the mandrel hole and filling with
proseal or removing and installing a new rivet. You may
have it drip from a rivet, but it might be 6 rivets away where it is leaking
out of the tank on one rivet and then leaching between the skin to the first
rivet that will let the fuel drip out.
Good luck,
Wayne
----- Original Message -----
From: "brian amendala" <n667ba@hotmail.com>
To: <oifa@irishfield.on.ca>
Sent: Saturday, January 11, 2003 2:38 PM
Subject: fuel tank
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reply from November below and I have also CC'd to the list as others
are/will be in the same boat.
If you go to bare aluminum "outboard" on each side of all filleted seams,
like I describe, the worry of bonding to old Proseal (or even sloshing
compound) is irrelivent although YES I do scrub the old proseal lightly as
well with scotchbrite to get the Proseal to hold to everything. The main
thing is to get fresh "membrane" of Proseal from bare aluminum to bare
aluminum across all the old fillets and where you come up the corners
(between the ribs and rear bulheads) from bare aluminum to bare aluminum on
each part and also the underside of the bulkhead flanges. Build it up in the
open corners between the rib and the bulkhead flange so that the Proseal
sits proud at all corners and goes onto the top of the flanges and ribs.
Then when it has harderned somewhat use an exacto knife to trim JUST ABOVE
the bulkhead/rib flanges feathering to bare aluminum about 1/2" to 1" in on
the flange. This way you'll have a skim of proseal that is bonded to the top
of the flange and a solid platform for the proseal to squeeze against in the
area between the rib and bulkhead flange when you put the top skin down, so
there will be no pin holes or leakage from the rear bulkhead. You should
also need to take a drill bit to clean out the first hole or two on each
bulkhead flange for the rivets before putting down the top skin, as it will
be filled in with Proseal if you did the corner filling sufficiently. These
bulkhead corners are the most common leakage area due to guys/gals trying to
put the top skin down and fill these areas in one process. It is very
important to have a cured (to semi-cured) "bath tub" created before putting
down the top skin. I go as far as letting the tank cure long enough before
installing the top skin that I can fill it with 100LL to the brim by tipping
the wing nose down to get as much fuel in as I can and letting it sit for a
few hours to watch for leaching or leaking (Water just doesn't work due to
it's surface tension). When you do this make sure all the lights are turned
on in the shop before starting (don't want no sparkies!!) or do it outside.
Wayne
............................................................................
............
Go to town with scotchbrite etc to get a clean bare
strip of aluminum completely around the tanks
perimeter/corners/stringers/top and underside of the rear tank bulkhead
flanges etc. You don't have to remove what's there, just
clean to bare aluminum along the sides of all existing fillets. This is what
I did with the Rebel that went to Maui. Then you can reproseal all seams,
give the rivets a coat and know that they are binding into the clean alum
surface to form a seal. Be sure to build a smooth lid seal at all the
bulkhead and rib junctions and let it cure before putting the lid skin back
on the tank. I also fill the tank with fuel while it's still open to make
sure it indeed is leak free in the "bath tub" configuration. Then I let it
air dry for a few days before I proseal down the lid.
Brian, With you leaving the .020 skin on through the tank you are basically
sealing
to it and the .040 skin is just reinforcement for the tank. As long as you
get the ribs/bulkheads sealed to the .020 you should be alright but it's
more important for you to have a seal around EVERY rivet otherwise your fuel
can run between the two skins and make it impossible for you to find where
it is really coming from. Anyone else would just have a dripping rivet that
can easily be fixed by undercutting the mandrel hole and filling with
proseal or removing and installing a new rivet. You may
have it drip from a rivet, but it might be 6 rivets away where it is leaking
out of the tank on one rivet and then leaching between the skin to the first
rivet that will let the fuel drip out.
Good luck,
Wayne
----- Original Message -----
From: "brian amendala" <n667ba@hotmail.com>
To: <oifa@irishfield.on.ca>
Sent: Saturday, January 11, 2003 2:38 PM
Subject: fuel tank
roughWayne, I have drilled off the top skin of my tank to re-seal it because I
have chased a leak around for a year and have come up empty handed. you
said you have completely re-sealed a rebel before and I was wondering what
the process was? Will pro-seal stick to exsisting pro-seal if I just
it up or do I need to so something else.
Thanks, Brian Amendala
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