First, my friendly A&P/IA and I (just A&P) did both tanks on my 56 170B in one day...concurrent with the annual. Observations: The tank panel screws were extremely difficult to remove, but we were prepared with the "old mans" tool from Brown Tool as some very astute folks recommended in this forum. Still broke a total of six screws, but were able to remove them. As others have found on their aircraft, mine had only two cork gaskets (one small & one large) per tank installed. We installed three when reassembling the filler neck. But there were NO small rubber gaskets??? on the filler neck screws on either tank. I know the Parts Manual calls for them, but none were there. Anybody have a source for those small gaskets/washers??? By the way, my humblest thanks for all the suggestions offered by our 170 experts.
The original part number for these rubber washers is 0311001-27. That p/n has been superseded to S350. Eight of them are also called for on the four screws that hold the windshield center strip in place and two for installing the original speaker to the roof. It's interesting that the same part number washer is used on different diameter screws. http://www.iwantcessnaparts.com has them for 71 cents. I'm not sure if that is for a pack of ten washers or each washer in a 10 pack.
fuel tank adapter washer.jpg
The screws cannot be tightened very much at all or the rubber washers will squish out and be useless.
Check out Parker's ThredSeal as a subtitute. They have a metal washer to retain the rubber ring inside. The rubber ring seals the threads. P/N 750-0002-10 would be the right size.
ThredSeal.jpg
You do not have the required permissions to view the files attached to this post.
Last edited by n2582d on Tue May 05, 2009 8:05 pm, edited 1 time in total.
Baby the tanks guys... I work for a shop that repairs them and many times they come in "too late to save". Small repairs might cost 250-400$ but if you do it right the first time you save money in the end.
Here are some tips for keeping your tanks leak free:
-Dont fill them all the way up. Some guys fill the tanks all the way to the top to get that "Maximum" range. However if you have a rough take off or some guy "Shakes the wing" to check for fuel, the momentum of the fuel pushes against the side of the tank and causes it to bend. Repeated bending causes the aluminum to crack(Much like breaking a paperclip)
-If you know a guy with "wet wing" tanks(ie riveted tanks on pipers) make sure they do not step or push on the tanks when they are full of fuel. This is why the riveted tanks leak.
-Tell the guy filling fuel to hold the nozzle while filling the tank instead of letting it just sit there. This resting of the hose while the tank is filled causes cracking around the filler neck
-When installing or removing tanks, make sure there is nothing under them to rub on. It sounds like something obvious but when worrying about a leaking tank guys often forget to notice a repair of the skin, longer bolts than original, and the odd left over rivet.
-Check threading first! If your tank leaks through the threads, make sure that all the fittings were meant to mate in the firstplace. Cross threading is very common.
-If it does not fit, dont force it in. If you crack around the fittings this is what likely caused it. If possible try and tighten all connections gradually from both ends. Dont tighten from one side and tighten as you go until you reach the tank you need some adjustments to make sure you have a perfect fit.
-Dont put slosh sealer into a dirty tank... follow the instructions and only do this once. There is nothing worse than cracking a tank open and finding 1/8" thick of sealer on the tank walls with everything from dirt to hair to ???
Sooner or later you will have to get the tank split, cleaned and repaired. This will cost ~1000 to do per tank. The other option would be to develop PMA replacement tanks but making them out of aluminum would be very costly(first tank would probably cost 100K to build-Notice how Almost all cessna tanks are the same?) so this leaves carbon fiber tanks. These seem to be hit and miss depending on who is actually doing the work. In the end they are also prone to cracking and they cost big $$$ to repair.
When I was still "working", I used to repair refrigator coils with an epoxy made for that purpose. This was usually done on an old unit that had been defrosted by a sharp pointed knife. It was usually a sucessful repair, and was under considerable internal pressure.
I have used the same process with excellent results on hairline cracks on aluminum fuel tanks. It requires scrupulously cleaning the crack area with a stainless steel wire brush and maintain the cleanliness until the epoxy is applied. I have never seen one leak again in the repaired area.
Cessna® is a registered trademark of Textron Aviation, Inc. The International Cessna® 170 Association is an independent owners/operators association dedicated to C170 aircraft and early O-300-powered C172s. We are not affiliated with Cessna® or Textron Aviation, Inc. in any way.
