Sealer for Fuel Filler Neck

[wa4jr]

I have fuel leaks in both threaded joints where the fuel filler neck screws into the fuel tank. What type sealant should be applied to the threads when the filler necks are reinstalled into the tanks? I cannot tell from the parts manual, but it looks as though I can just unscrew the filler necks with carefull application of a chain wrench without having to take off any of the flanges or gaskets that surround the neck. Am I correct in this assumption? I need to get the leaks repaired before the installation of a Monarch fuel cap and moat cover kit. Thanks for the help.

[c170b53]

Mine are staked in which will require blending otherwise the threads will pick up material upon neck removal. Prc sealant should seal the new necks threads.

[GAHorn]

Pro-Seal PS 890 B is the correct stuff. But Aircraft Spruce 877/477-7823 sells a generic replacement for 1/3rd the price. Their PN 09-38510 for $18.95.
Be careful doing this job. Steel tools can spark when they slide/grip steel filler necks. (Ground the tool with a jumper wire before using it, and use a large fan to direct a breeze so as to blow fumes away from you when removing the necks.)

[wa4jr]

Uhoooh, I hope mine are not staked in! Why would they do that? I'll have a closer look and if the necks are indeed staked in place then I just won't worry about it and leave it as is. I am going on with the Monarch moat seals, so that will end the problem of rain water getting in the tanks via the moat and leaking filler neck threads, but I just did not like the idea of fuel coming out of the tanks when full and filling the moat up under the new Monarch moat covers. Perhaps a healty bead of the proper sealer could be applied at the base of the filler neck instead of removing them if they are staked? Thoughts and ideas? Thanks for the tip George....or I could use this time as a chance to drain my tanks and refill them just to enter into the "how much does my tank really hold" contest

[wa4jr]

I tried a little experiment recently to try and cure my fuel loss out of the right wing tank. Thinking that most of the fuel was coming out of the vent valve in the right tank cap, I applied a little JB Weld to the vent holes, verified the vent system was working and then went flying. So after five hours do you thing the leak went away. Heck NO! This little experiment showed me just how bad the leak is in the treaded joint between the filler neck and tank. Since the factory vent system worked so good, the tank pressurized during flight and just pushed fuel out of the tank around the threaded joint and all over the plane. What a MESS! I know the Monarch moat seals and caps would probably cure my problem, but I hate to have that leaky threaded joint up under the new moat seals.

So my problem now is how to get the filler necks off the tanks. Not as easy as just screwing them off, as some Dilbert thought it would be really neat to center punch the neck into the tank threads thereby insuring damage upon disassembly. What is the recommended method for minimizing damage to the fuel tank while screwing out filler necks that have been staked in place? Thanks in advance for the help.

[n3439d]

the sealant that is in your monarch kit is the correct stuff to seal the threads.

[wa4jr]

Yes I know the Monarch sealant is good stuff, but I don't want to "cover up" the leak with the moat seals and have the fuel welling up in the moat under the seal plates...then wicking into the wing structure. I need to know if there is an alternative to the "big wrench" method for getting the staked fuel filler necks out of the tanks so that I can clean and reseal the threads. Do I just use a monster chain wrench and power the necks out of the tanks with the staked area raking the internal threads...or is there another way? If I could find the Dilbert that got his jollies by staking my filler necks...I'd hold a scatter gun on him while he struggled with taking apart the mess he created. I wish when some folks do MX on an aircraft that they think about the next person that is going to have to come back after them to service the part in question

[Roesbery]

As a caution, I talked to a fellow the other day who has a cabin out away from the crowd. He flew his C-185 out there for a few days R & R, noticed he had a bad fuel leak the next morning, ground wet with fuel, hot sunny day, got out some tools to fix the leak, Dropped a tool on the ground, sparked on a rock. Within 5 minutes the nice 185 was a few pieces of molten aluminum in a black spot. Said he couldn't beleave how completly and fast it went.

[GAHorn]

Working with steel tools around any fuel tank is a hazard. Aluminum tools are best. Don't know how a Sears strap wrench might do.
But in any case, I know of no shortcut to simply unthreading the neck from the tank. Without actually seeing the "stake" job, I can't make a judgement, but chances are it'll come out just fine. The neck is steel and should survive fine.
Are you sure your leak is not coming from the cap gasket where it mates with the neck? Those are inexpensive and available from Spruce.

[wa4jr]

THANKS George! Been looking for a reason to go out and get a pair of those neat strap wrenches...NOW I have a reason to do so. Would be better than my original idea of using my trusty chain wrench. Not too worried about fire as I use that mogas stuff which is almost inert compared to 100LL I suppose I will bite the bullet and just go ahead and use the strong-arm method and power the necks out of the tanks...will just try not to think too much of the damage the staked area is doing to the internal threads of the tank during this process. An extra thick application of sealer should fill the damaged areas anyway...right No George, the washers and caps are new. I tried the easy fix first...although after ordering the new caps from Spruce was when I found out that they are not legal on certificated aircraft. I think I will videotape the entire ordeal and then send the tape in to Bob Villa at Craftsman Tools and get famous for a new application of their strap wrenches

[spiro]

if I were going to remove a threaded and staked filler neck I'd try to at least partially "unstake" it first. I'd think a big pair of channel locks is what I'd try first. You could certainly drill out the stake but then you'd have to deal w/ resealing the hole.

you sure you don't want to try injecting sealant w/o pulling the necks?

[c170b53]

If your installation is like mine ( I have 175 wings), the base of the filler neck is inside the tank where it screws into a base flange. The flange is held in place with the six screws that hold the splash shield in place. There is also a seal between the base and the inside of the tank. The stakes in my filler neck are very deep and I think you will rupture your tank skin near the six aforementioned screws if you strong arm the neck out. I don't know if removing the fuel gauges allows you access to pull the base out. If not you may have to destroy the filler neck into segments,pull them out and replace the seal after dressing out the stakes or just allow the base to drop into the tank (thethered) and replace the seal. Lots of good advice here its only short with respect to practical approaches to maintaining old planes. Flame suit on.

[newfie175]

I had to replace the fuel filler neck on 175. Everyone made it sound trouble some. I made a T wrench to fit the cap. A 3ft bar with a piece of 1/2 in flat bar welded in the center. The flat bar is 3ins. long and I tapered it from 2 ins down to 1 3/4 ins. This fits down in the cap lock. When you turn the pipe in or out, you are applying pressure in both directions and you are not twisting the metal. Took out 4 and put in two without a problem. Will worth $30 at welding shop.

[hilltop170]

Newfie175 has the right idea. I would not wrap anything around the outside of the neck and try to unscrew it. Whatever you use will probably deform the neck. Any flat bar stock of the correct width and thickness that will slide down into the neck and catch the inside of the neck would be best. When that is twisted with a large wrench or better yet, two large wrenches, one on each side, those will apply pure torque to the neck without collapsing it from the outside like a strap wrench or water pump pliers will.