Cessna Wing Skins

Don't drill out those rivets! They are only holding a circular
gasket flange ring on the top skin. After all the screws are out, you
have to be a little less gentle with that skin and lift it enough that
the gasket flange ring will clear the tank neck and allow the skin to
slide out from under the leading edge skin and cabin roof skin.
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on. (Line boys with their big
fuel nozzles tend to let the tank neck take the hose weight, and that
cocks the tank neck and cracks the weld.) Once the mechanic has done a
couple of these inspections they're not a big deal. The skins are much
harder to get back into place thatn they are to take out, especially if
the tank was moved a bit; the filler neck will no longer line up with
the skin when the skin's screw holes are lined up with the wing's
holes.
You'll need a couple of new gaskets for the filler neck, at
typical Cessna prices.

Dan

Thank you very much Dan for the info.
Tom
wrote in message
ups.com...
Don't drill out those rivets! They are only holding a circular
gasket flange ring on the top skin. After all the screws are out, you
have to be a little less gentle with that skin and lift it enough that
the gasket flange ring will clear the tank neck and allow the skin to
slide out from under the leading edge skin and cabin roof skin.
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on. (Line boys with their big
fuel nozzles tend to let the tank neck take the hose weight, and that
cocks the tank neck and cracks the weld.) Once the mechanic has done a
couple of these inspections they're not a big deal. The skins are much
harder to get back into place thatn they are to take out, especially if
the tank was moved a bit; the filler neck will no longer line up with
the skin when the skin's screw holes are lined up with the wing's
holes.
You'll need a couple of new gaskets for the filler neck, at
typical Cessna prices.

Dan

wrote:
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on.
snip

I'll second that assessment. Tank skins need to be pulled far more
often than most people bother to pull them. The OP's mechanic is doing
his job.

See our recent experience on my site. Click through:

Aviation-Articles-Maintenance-Fuel Tank Repair

-Doug

--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

Good article. Your airplane has an older style fuel cap and flange
arrangement than the original poster, and his skins are more difficult
to remove. His advantage is not having that recessed pit around the cap
that collects water and dirt; the cap flange is flush with the wing.
His disadvantage is getting that gasket back into place while replacing
the skin; a bit of fuellube will hold it in place. I suspect his tank
skin is being hard to remove because someone used Form-A-Gasket or
something tough to seal the gasket last time, and it's stuck good.
172s used all-brass floats by the time our L and M models came
out. They're OK, but we had one fail because the arm stop was
misadjusted and the float was tapping the top of the tank when the tank
was full of fuel. It wore a hole in the float, which filled and sank.

Dan

wrote in message
ups.com...
Good article. Your airplane has an older style fuel cap and flange

That is correct Dan. My cap is flush with wingskin. Once I get it the skin
loose,
the skin will slide across the neck.

a bit of fuellube will hold it in place. I suspect his tank
skin is being hard to remove because someone used Form-A-Gasket or
something tough to seal the gasket last time, and it's stuck good.

Yes, I saw the hardened sealant when I removed the screws. There is
definitely
no way or place to pry or use a tool to losen the skin without ruining any
components so
it is going to be interesting.
\The Cessna manual calls for some specific types of sealant to use, one
being
a Dow Corning product, and others.
I have not ordered any gaskets yet as I am waiting to see if I to need any
other
components such as tank restraining straps, chafe protection, rubber tank
supports,
top skin straps, and the sealant.
Tom

Good one. Thanks!

On 24 Apr 2005 20:01:30 -0700, wrote:

Don't drill out those rivets! They are only holding a circular
gasket flange ring on the top skin. After all the screws are out, you
have to be a little less gentle with that skin and lift it enough that
the gasket flange ring will clear the tank neck and allow the skin to
slide out from under the leading edge skin and cabin roof skin.
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on. (Line boys with their big
fuel nozzles tend to let the tank neck take the hose weight, and that
cocks the tank neck and cracks the weld.) Once the mechanic has done a
couple of these inspections they're not a big deal. The skins are much
harder to get back into place thatn they are to take out, especially if
the tank was moved a bit; the filler neck will no longer line up with
the skin when the skin's screw holes are lined up with the wing's
holes.
You'll need a couple of new gaskets for the filler neck, at
typical Cessna prices.

Dan