Fuel Tank Filler

[n2582d]

Considering the amount of work involved in replacing these 6-hole fuel adapter gaskets (p/n 0523532) this is not a job one wants to repeat so it’s important to get the correct material to do it right the first time. Viton seems like a good way to go although Real Gaskets does not have a PMA to make them. If making them out of cork I would be reluctant to use cork sheeting from places like McMaster-Carr or your local auto parts store. You want cork that meets AMS-C-6183 (MIL-C-6183) Class I. Not sure about the best hardness — probably Grade C (firm)? Check out the following chart I found here.

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McFarlane sells 1/16" thick gaskets. To prevent water from seeping in past the fuel cap gasket do not use thicker gaskets. See this post for further explanation.

[DaveF]

Viton? Thanks a lot, guys. You’re going to get me to reseal the tanks a third time?

[rnealon1]

Okay dug into this and found if I twist the cap on all the way it is about 60 degrees past center (same on both caps).

Trying to make sure I understand how to correct this and what parts I would need.

Theoretically I could remove 6 inner screws, rotate 60 degrees counter-clockwise, and reinstall screws?

Obviously it makes sense to install new gaskets and I see the difficulty of doing this for the inner one.

In the IPC picture it looks like item 39 is the adapter to fuel tank outer gaskets but is listed as 0523531 Gasket - Strainer. Item 25 looks like the inside gasket and is listed as 0523532 Gasket - Fuel tank adapter.

Curiously 532 is listed by McFarlane at $9.12, while 531 is listed for $54.91. Are they that different?

Finally if sealing gaskets what sealant is recommended?

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[sfarringer]

Explain to me how the skin will attach, if you rotate the assembly to a different orientation?
Make new skins?
What am I missing?

[n2582d]

Steve,
This is what we've struggled to communicate throughout this thread. This is partly due to the fact that the 170B IPC doesn't illustrate in fig. 2 or fig. 7 the aluminum collar that the fuel neck screws into. It is this assembly -- the collar and the fuel neck -- that can be rotated in 60º increments to best align the fuel cap tabs. To reiterate what we've all tried to say in this thread: The adapter plate (p/n 0523529) cannot be rotated; it will only fit one way. This illustration from a C-172 Service Manual includes the bottom aluminum collar. Cessna adds to the confusion here by referring to both the aluminum collar that the fuel neck screws into and the moat around the fuel neck as adapters.

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[cessna170bdriver]

Theoretically I could remove 6 inner screws, rotate 60 degrees counter-clockwise, and reinstall screws?

Your A&P would be the one to ask but this would be what I’d do, if you can get filler neck collar loose from the inside of the tank skin without disturbing the joint between the moat and the outside of the tank skin.

Obviously it makes sense to install new gaskets and I see the difficulty of doing this for the inner one.

The inner one wasn’t as hard as it looked. It will fold enough to get through the hole in the tank while you hold the neck by the chain. If you have an old gasket on the inside the hard part will be cleaning the mating surfaces and getting the debris out of the tank.

In the IPC picture it looks like item 39 is the adapter to fuel tank outer gaskets but is listed as 0523531 Gasket - Strainer. Item 25 looks like the inside gasket and is listed as 0523532 Gasket - Fuel tank adapter.

The 0523531 gasket is the one with 8 holes that goes between the moat and the top cover (wing skin). There are two 0523532 gaskets (6 holes), one between the moat and the top of the tank, and one between the filler neck flange and the inside of the tank.

Curiously 532 is listed by McFarlane at $9.12, while 531 is listed for $54.91. Are they that different?

Finally if sealing gaskets what sealant is recommended?

These are two of the reasons I went with the viton gaskets. Both sizes of the viton gaskets are about $35 each making the viton a little cheaper in total for the three gaskets, and the fact that the Real Gaskets instructions emphasize their gaskets are to be installed DRY, avoiding any messy sealants. As far as approval, my AI thinks the viton gaskets are better than the cork and is just going to do a logbook entry.

[cessna170bdriver]

This photo might help explain he filler neck assembly for those who haven’t seen it. I didn’t understand it myself until I got mine apart. As I’ve mentioned before, there should have been another gasket inside the tank like the one I’m holding.

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[n2582d]

Miles,
With those 1/16” edit: 1/8” Viton gaskets how does the height of the top of the fuel neck compare to the top of the fuel tank cover? I wrote about this here. In thinking further about this — as the fuel filler neck does not sit level when the plane is on the ground — water will drain from the moat before it will enter the tank even if the filler neck is slightly lower than the top skin level. In other words, should I be mute about this moot moat issue?

[cessna170bdriver]

Gary, I assume you meant 1/8” Viton gaskets. I haven’t asembled mine yet, as I inadvertently ordered coarse thread screws, and I’m waiting on the correct ones to arrive. Discounting any compression of the gaskets, I’m assuming the neck will sit 1/16” lower in the tank, the moat will sit 1/16” higher above the tank, and the cover 1/16” higher above the moat, so the top of the filler neck will be 3/16” lower relative to the top cover.

[rnealon1]

Miles this is very helpful thank you. I think I finally understand.

Bob

[DaveF]

Be careful not to change the height of the top surface of the eight hole plate. Keep it at the correct height for the top wing skin. If the total height of the tank plus filler neck is too large, the eight-hole plate will be higher than the wing skin to which it attaches. Similarly, too small and it won’t reach.

[sfarringer]

Thanks for clarifying all the pieces involved!

While it does fix some of the inadequacy of the '48 Ragwing fuel fillers, it sure doesn't appear to be an elegant solution!

[cessna170bdriver]

Be careful not to change the height of the top surface of the eight hole plate. Keep it at the correct height for the top wing skin. If the total height of the tank plus filler neck is too large, the eight-hole plate will be higher than the wing skin to which it attaches. Similarly, too small and it won’t reach.

Miles,
With those 1/16” edit: 1/8” Viton gaskets how does the height of the top of the fuel neck compare to the top of the fuel tank cover? I wrote about this here. In thinking further about this — as the fuel filler neck does not sit level when the plane is on the ground — water will drain from the moat before it will enter the tank even if the filler neck is slightly lower than the top skin level. In other words, should I be mute about this moot moat issue?

I got the right side put back together a couple of days ago. To address Dave’s concern, even with the thicker gaskets the tank cover skin still fits smoothly over the adapter. I don’t know what the height of the filler neck was before, but it is now about 3/16” below the curvature of the skin. However, to address Gary’s concern, as best as I could tell using an inclinometer, it is still slightly above the lowest point at the rear of the opening, with the airplane on a fairly level floor in the three-point attitude. After I’ve flown with full tanks to ensure the new gaskets keep fuel in the tank, I could pour some water in the adapter (moat) to verify that measurement. (Of course, with a good gasket under the filler cap itself, its shouldn’t be an issue anyway.)

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[n2582d]

Looks great Miles!

[GAHorn]

For the adventurous among us…. Be reminded that the “Filler Neck” is threaded into the Adaptor. When being assembled to each other is an excellent moment to configure them so as to result in aligned fuel-cap-tabs. They are then “staked” to discourage it becoming misaligned again.

I’ve never done this task….but it’s tempting to the imagination to see how difficult it might be to overcome the staked-neck to rotate it to an aligned position.