The International Cessna^® 170 Association

I am ready to begin gathering the required parts needed to remove my fuel tanks, replace the 3 gaskets around the fuel filler, replace the neopreme pads under & over each tank and the connecting fuel hoses including those on the vent line. Its a project that will likely not take place until sometime this summer, but now is the time for me to get everything together. I dread the job, but I have had leaks at the fuel cap/filler for several years and know it is the gaskets that need replacing as they and the hoses, pads, are 53 yrs old so rather than just replace the 3 gaskets on each side, I am going to do the project that Jim Wildharber did prior to the Techachapi convention. I have Jim's data, which will be helpful, but I (as usual ) have some questions. First I am thinking of replacing the six (6) screws that hold the fuel tank adapter (AN 520-10R10) with stainless screws if they are available because they sit in the bottom of the moat (adapter) and are subject to standing water if the plane is out in the rain. Any reason not to do so? Are stainless screws of this part number available? Next, what are the various sources for the fuel filler gaskets (3 each side)? The neopreme "pads" (0523521-5 & 0523521-6) that must be those that are under the hold down straps and on the ribs under the tank, plus possibly the small pad on the "block" can likely be fabricated from sheet neopreme purchased at vrs local suppliers, but I don't know the thickness of the material. Jim W. mentioned that he used some which was a bit thicker than original and it make reinstallation of the tanks a BEAR! I would like to avoid that if possible. Anyone know what the correct thickness should be? I noted that Spruce has anti-chafe molding available that accomodates staps up to 1 inch in width (their part # 05-01800) but without the proper thickness data I don't know if that would work or not. Finally, my 56 C-170B parts catalogue and my C-172 parts catalog's specify the number of vrs length/size screws needed for the wing panel that has to be removed over each tank, but it doesn't specify which length screws go where (seems there are 4 sizes--NAS 228-12; -9; -8 & -7's). Nothing in there about where the different sizes go in the panel. I seem to remember when I removed one of the panels years ago that the ones across the leading edge of the panel were longer than the others, but I might have that reversed. I don't recall there being 4 different lengths, but that was a long time ago and I likely didn't recognize but 2 different lengths at the time. Sort of thinking about getting all of the screws in stainless if available. Suggestions appreciated.

If you add the letter "C" to the end of the part no.... you will be describing the "Corrosion resistant" screw (stainless). The part number of the pads have been superceded to S2127-1-25.12 If you call Yingling they can probably tell you the thickness.
If you carefully observe the screws as you remove them you'll see which length's go in which positions.

170C wrote:First I am thinking of replacing the six (6) screws that hold the fuel tank adapter (AN 520-10R10) with stainless screws if they are available because they sit in the bottom of the moat (adapter) and are subject to standing water if the plane is out in the rain. Any reason not to do so? Are stainless screws of this part number available?

According to Genuine Aircraft Hardware Co. http://www.gen-aircraft-hardware.com AN 520-10R10 has been superseded by MS35207-264, a low carbon steel cad plated pan head screw. You could also use a structural pan head screw with corrosion resistant steel MS27039C-1-10 or if you wanted stainless (non-structural), MS51958-64. My preference would be option #2. Stick with pan head screws as the flat area in the moat is only .330" wide. A washer head screw will end up riding on the radius of the moat. Also don't forget the o-ring "washers" under the screw heads. See http://www.cessna170.org/forums/viewtop ... 405#p56405 for related ideas.

170C wrote:Next, what are the various sources for the fuel filler gaskets (3 each side)?

It might be cheapest to have them "owner produced" at a local shop. Otherwise google the part number and look for the best deal. A quick search found 0523532 for $13.25 and 0523531 for $15.60 at http://www.airward.com

170C wrote:The neopreme "pads" (0523521-5 & 0523521-6) that must be those that are under the hold down straps and on the ribs under the tank, plus possibly the small pad on the "block" can likely be fabricated from sheet neopreme purchased at vrs local suppliers, but I don't know the thickness of the material. Jim W. mentioned that he used some which was a bit thicker than original and it make reinstallation of the tanks a BEAR! I would like to avoid that if possible. Anyone know what the correct thickness should be? I noted that Spruce has anti-chafe molding available that accomodates staps up to 1 inch in width (their part # 05-01800) but without the proper thickness data I don't know if that would work or not.

The hold down straps are 1/2" wide .040" aluminum. Each strap is roughly 44" long. My strap had 3/4" wide, 1/16" thick rubber glued on with contact cement. Probably not original. You could go with this from Brown Aircraft Supply: There are seven hat sections all together in each wing fuel bay. 6 are 33" long and the one that is near the filler opening is 25" long. The top of the "hat" is 5/8" wide. Order at least 223" of anti-chafe material to cover each hat section in ONE wing. You might consider Aircraft Spruce's p/n 05-00664 silicone anti-chafe seal kit or order directly from Gee-Bee Aero Products 800-556-3160 / n77gb@msn.com

170C wrote:Finally, my 56 C-170B parts catalogue and my C-172 parts catalog's specify the number of vrs length/size screws needed for the wing panel that has to be removed over each tank, but it doesn't specify which length screws go where (seems there are 4 sizes--NAS 228-12; -9; -8 & -7's). Nothing in there about where the different sizes go in the panel. I seem to remember when I removed one of the panels years ago that the ones across the leading edge of the panel were longer than the others, but I might have that reversed. I don't recall there being 4 different lengths, but that was a long time ago and I likely didn't recognize but 2 different lengths at the time. Sort of thinking about getting all of the screws in stainless if available.

My parts book shows 14 NAS228-12 screws and 37 NAS 228-8 screws on fig.7-45 and 7-46. The 14 longer ones go along the leading edge (through the front spar). Do not use stainless screws here as stainless is non-structural. As the NAS part numbers are obsolete use 37 MS27039C0808 and 14 MS27039C0812 corrosion resistant screws. Dip the screws in zinc chromate before installing them--it'll help the next guy get them out.

Gary, when they fire me I'm nominating you. (Thanks)

Thanks for all the good data guys

gahorn wrote:Gary, when they fire me I'm nominating you. (Thanks)

Thanks George! I think I can speak for all of us when I say your job here is safe. In fact I think the Association ought to double your pay! Over 8500 posts. That is a LOT of work. We appreciate it!

Time to make a deal. Back in 1959 Cessna Service Letter 170-172-19 called for filling the void between the filler neck and the fuel tank adapter with Parker Seal-Lub. The letter also instructed one to coat the screw threads with the Seal-Lub. Later, in 1970, Cessna issued Service Letter SE70-28 which again called for sealing this void. This letter, however, called for silicone seal or non-hardening Permatex No.2. Some on this board have suggested using Pro-Seal. Ole Pokey, (or anyone else for that matter) if you buy a pint of Pro-Seal and only use half, I'll buy the other half for half the cost.

Pro Seal is also available in smaller tubes for about $17.



http://www.aircraftspruce.com/catalog/a ... ealant.php

Actually, if you read closely, that is a sealant made by Flamemaster (Chem Seal). I'm sure it would work fine in sealing the tank inlet area. Here is an informative article on sealants--probably more than anyone cares to know. http://www.vansairforce.net/articles/tank_sealant.pdf

Gary is referring to the picture George posted as being to smaller amounts of pro-seal type stuff. Gary is correct this product pictured by George is Chem Seal if you look closely at the Spruce info. I'm familiar with the real PRO-SEAL sold in the containers in the first photo which is why I mentioned it.

I've not used Chem Seal but wouldn't be afraid to use it. Actually didn't realize there was different companies making pro-seal. I wonder what my company is using on the helicopter I fly?

Frank, I've attached templates of the filler neck gaskets you will need. Print them and cut your own before you start the tank removal. If your not satisfied with your owner produced parts then buy them.

The Flamemaster brand is what Van's aircraft sells for sealing the built-up leading edge fuel tanks on RV aircraft. The name Proseal has become a generic term for tank sealant just like Kleenex has become generic for tissues. The stuff in the picture George posted is mixed in and dispensed from the same container to cut down on the mess. The downside is that you have to mix all of it at once. Unused quantites of mixed sealant can be stored in a freezer, but not indefinitely. According to a spec sheet I read, the working time approximately doubles for every 10 degree F drop in temperature. I believe it can be purchased in quantities as small as 2 oz.

Miles

And on the level of the painfully obvious, the tank won't come out of it's bay unless you remove the outlet fitting. My small contribution... Russ Farris

It's my turn to do the job that's the topic of this particular thread. Even though the thread is almost a decade and a half old, its still pertinent.

To all of you who contribute, THANK YOU.

Jim Wildharber presented a detailed description of all that his required on his B model: viewtopic.php?t=10345