The International Cessna^® 170 Association

DaveF wrote:No way I’d use a tool like that with the flange still attached to the tank. If you had things taken apart for tank re-sealing, you’d be able to apply solvents and heat, then the wrench, without damaging the tank.

The problem is that the flange to which the filler neck is screwed onto is installed in the tank prior to the top and bottom of the tank being welded together. The IPC gives one the impression that the filler neck is screwed onto the adapter plate but that's not the case. See this thread for pictures. I have no idea if this filler neck from Aircraft Spruce is the correct size but might be worth looking into if considering reclocking the filler neck.

ghostflyer wrote:I may be wrong about this, but some where in the back of my brain is telling me you can adjust the cap pawls to suit. ...

The C156003-0101 all metal fuel cap has two tabs that "capture" the metal plate which secures the cap to the filler neck -- no way to adjust or clock this cap.

n2582d wrote:The problem is that the flange to which the filler neck is screwed onto is installed in the tank prior to the top and bottom of the tank being welded together.

Right, I forgot about that. When I had my tanks out for filler neck re-sealing I pondered the assembly for a while. Like the straps that hold the tanks down, they don't seem fully designed for maintenance.

Thanks george , I owe you a beer. I have about 8 caps in the junk box in the hangar that have a u/s flapper valve and /or the large sealing washer that’s u/s . In the past I have tried to buy new valves but have been unsuccessful. A new fuel cap in this country is about 150 dollars .

Just got back from the hangar looking for my spare fuel caps ,spark plugs and air filters. It was during covid lock down that my toilet paper went missing in my hangar . There was a rush on toilet paper in the supermarkets . However some one had a duplicate key for my hanger. Now I find also my stash of tank caps are missing plus I had a box of new spark plugs for my aircraft and a spare new air filter element. ALL gone except there was ONE spark plug left in the box. Not happy. I had a look at a spare cap that i carry around in my aircraft and this can’t be spit apart . It’s the same that’s illustrated previously . However saying all that I can recall having tank caps that had a castellated nut on the bottom and where you hooked up a chain. Note. the locks have been changed .

ghostflyer wrote:Just got back from the hangar looking for my spare fuel caps ,spark plugs and air filters. It was during covid lock down that my toilet paper went missing in my hangar . There was a rush on toilet paper in the supermarkets . However some one had a duplicate key for my hanger. Now I find also my stash of tank caps are missing plus I had a box of new spark plugs for my aircraft and a spare new air filter element. ALL gone except there was ONE spark plug left in the box. Not happy. I had a look at a spare cap that i carry around in my aircraft and this can’t be spit apart . It’s the same that’s illustrated previously . However saying all that I can recall having tank caps that had a castellated nut on the bottom and where you hooked up a chain. Note. the locks have been changed .

Soooo….now that the chickens have all been eaten…. you’ve gone and bought a fox-hound…??

rmorton wrote: ↑Thu Jan 26, 2023 10:55 pm …

Since the neck is attached to the tank with 6 screws, we can only adjust in 60 degree increments. So getting to 90 degrees by turning the whole assembly isn't going to work. We have it taken down to the same level as Jim Wildharbor shows in his powerpoint. I can't see how the neck is "staked" to the piece in the tank, but the threads appear to be very well sealed.

Any other thoughts or ideas besides just accepting it as is?

Oh, and one other interesting discovery - the inner tank gasket was altogether missing on this tank! I can see where that could get overlooked when referencing the IPC because it doesn't show the inner gasket in the diagram.

I’m in the middle of replacing ‘98C’s filler neck gaskets, and in my research before starting I ran across this thread. If your cap is off by some multiple of 45 degrees, the upper half of the neck is not clocked correctly. Edit: the clocking of the cap can’t be off by 45 degrees. The six screw holes around the tank opening only allow installation in 60-degree increments. I’m a little slow sometimes, but I usually get there… I took the photo below right after removing the tank cover, before removing the six screws fastening the top and bottom pieces of the neck to the tank, so it shows the correct clocking (my caps line up correctly). Note that that there two holes in the 6-hole pattern that exactly line up with two holes in the 8-hole pattern. The line through those four holes should run spanwise to the wing. Also note that the notches for the cap ears should be at 2 o’clock and 8 o’clock as seen looking aft from in front of the wing; if they aren’t the cap will be off by some multiple of 60 degrees.

cessna170bdriver wrote: ↑Wed Jan 22, 2025 7:39 pm… If your cap is off by some multiple of 45 degrees, the upper half of the neck is not clocked correctly.

IMG_4613.jpeg

As the eight tank cover holes and the six holes around the tank filler hole are in fixed relation the adapter can only be correctly clocked one way — (actually, two ways as it can be 180° off). It’s only the filler neck’s collar that can be indexed 60° or 120° off onto the adapter/moat.

I had the terminology incorrect; what I called the upper half of the filler neck is actually the adapter - the part with the inner 6-hole circle for attaching the neck to the tank, and the outer 8-hole circle for securing the tank cover. In any case the line where two holes in the 8-hole circle align with two holes in the 6-hole circle needs to run spanwise to the wing.

Miles,

Where did you source the gaskets, and how difficult was removing and replacing?

My fuel caps are both 45 degrees off when twisted fully on; I would like to correct this.

Thanks,

Bob

When they’re not in alignment with the relative wind…..You’ll sleep better if you Think of them as vortex-generators.

They can only be adjusted in 60 degree increments.

It might be 60 degrees, I need a protractor. Does seem to help with STOL performance

I’ve bought the gaskets from McFarlane and I’ve also made them myself from sheet material using the templates that Bruce has posted. The McFarlane gaskets seem kind of expensive, but making them myself took a long time and I wasn’t happy with the result. Gasket material is difficult to cut with precision.

Rotating the cap assembly isn’t easy. First you have to remove the upper wing skin, which is annoying because it’s tucked underneath the leading and inboard skins.

The real problem is that when you remove the six screws and free the cap assembly, the lower gasket (the one that’s inside the tank) will probably disintegrate and drop a bunch of particles into the tank. And if you have to scrape old sealant before installing a new gasket, you’ll get more crud falling in. Last year when I resealed my tanks I didn’t completely remove the tank, I did the job in place and hoped I could vacuum out all the bits. Error! A year later I’m still sumping black particles. Ten years ago I did it the right way and pulled the tanks completely out, but that's a lot more work.

Here’s a view of the cap, showing the inner gasket. If you do this job be sure to seal the six screws and their threads or you’ll have leaks.

rnealon1 wrote: ↑Sat Jan 25, 2025 7:18 pm Miles,

Where did you source the gaskets, and how difficult was removing and replacing?

My fuel caps are both 45 degrees off when twisted fully on; I would like to correct this.

Thanks,

Bob

Bob, I decided to use the viton gaskets (RG-0523532 and RG-0523531) from Real Gaskets of Tennessee. I made that decision mainly based on the fact that they don’t require sealant. I had thought about using EZTurn on them, but noticed the instructions that came with them emphasizes that they be installed DRY.

I’ve read of people having issues removing decades-old tank cover screws, but mine were all new less than 10 years ago and for the most part came out without protest. Just make sure you use a high quality #2 Phillips screwdriver or bit.

I have the gaskets in hand but haven’t installed them yet. When I went to install them a couple of days ago, I was checking the hardware against IPC and noticed that the six screws that had fastened the adapter and filler neck to the tank are only 1/2” long as opposed to the 5/8” called for. The 1/2” screws were structurally sufficient probably because the gasket between the filler neck flange and the inside of the tank was missing, allowing sufficient thread engagement in the filler neck flange. Because the viton gaskets are about 1/8” (actually 3mm), and there will be two of them instead of one 1/16” gasket I ordered 3/4” screws in addition to the 5/8” ones to make I’ll have the right ones for the job. I’ve also ordered some #10 cork sealing washers from McMaster-Carr (which were also missing before).

cessnut wrote: ↑Sat Jan 25, 2025 8:43 pm They can only be adjusted in 60 degree increments.

Correct! I had thought that clocking the adapter plate off by one hole relative to the tank cover skin might put the cap off by 45 degrees, but the 6-hole screw pattern around the tank opening would preclude that being possible.