The International Cessna 170 Association

Some recent discussions on Fuel Tank repairs prompted me to post a few notes and pictures of how our plane did last year. My younger son Marc and I did the work and it went OK. The notes everyone has posted on removing the screws is great advice. We pre-soaked starting a week before with a little spray on each head daily. Most came out fine. The big suprise was when we pulled the tank. The door catch that is attached to the underside of your wing is held in place with 4 machine screws. The two aft screws that do not go through the spar were to long. The ends of the screws were wearing on the tank and about a fraction away from putting two holes in the tank.

The two aft screws should be 3/8" in length and no more (I did not find a number for the screw in my IPC)

I'll post 3 pictures: One the tank, and you can see the indentations. Two, the channel bracket inside the tank bay they thread into (IPC Fig.#8 p/n 0523004-2). And third, the bracket without the two aft screws (IPC Fig.#8 p/n 0523004-11). .

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I hope you find this helpful. I will also do another post of the tank and tank bay work.

Kyle,
Thanks for the write-up and pictures. According to SNL 10-24-57 Cessna changed from regular nutplates to capped nuts on the C-172 at s/n 28500 "to protect the fuel tank against over length screws." One Cessna p/n I found is 22NA1K-02 - not sure if that is an anchor cap nut or not. How much clearance do you think there is between the mounting surface of the nutplate and the bottom of the fuel tank? Would two NAS1474 capped nutplates (with one leg ground off of each) work? The NAS1474-A3 is for a 1032 screw and has a height of .405". Too tall???

Hi Gary, I think they would be to tall. As built, that bracket's inside dimension is only about a 1/4" tall and with a screw of 3/8" length it comes right up flush with the top surface of the nutplate. The 1/2" screws I had installed protruded enough (about 1/8") out of the top of the nutplate to come in contact with the tank. And that's with the thickness of the door bracket, wing skin, and finally the nutplate bracket. Just glad my mistake didn't cause anything worse

Kyle