170B Fuel Tank

N170CT · Post by **N170CT** » Tue Feb 10, 2004 8:25 pm

Ladies & Gentlemen,
Continuing on with an earler question about removing the screws holding the upper wing skin......somewhere I read a discussion on replacing the gasket/seals on the filler neck assembly (Not the GAS CAP) and was told that each tank filler neck requires two each of one part number cork gasket and one each of a second part number, which is a larger cork gasket. But the 170 parts manual illustrates only one of each gasket. Where o where in the assembly does that second small gasket go??? Yeah, I know replacing these gaskets will not make my airplane go faster, but it will help the fuel consumption.

jlwild · Post by **jlwild** » Tue Feb 10, 2004 8:53 pm

George Horn answered this for me in an email recently. I ordered the gaskets from Hill Aircraft 1-800-998-7832. Part no. 0523532 cost $11.92 and part no. 0523531 cost $22.16.

They were illustrated in my 170B parts manual under Figure 2, items 25 & 39 and 170A parts manual under Figure 7, items 5 & 19.

I am still in the process of installing mine; hangars to cold to work in right now.

wa4jr · Post by **wa4jr** » Wed Feb 11, 2004 12:53 am

Yes,

indeed! These are special cork gaskets to work with solvents such as gasoline at these prices, are they not? If they are plain cork, then fabricating one's own gaskets from cork sheet would save a great deal of money...unless cork has gone way up recently. I need these gaskets for a resealing project this week, but think I'll call around a bit. Maybe Sacramento Air Ranch has a better price?

wa4jr · Post by **wa4jr** » Thu Feb 12, 2004 2:22 am

I just took my right tank filler adapter apart today and found a few surprises. The 170 parts manual only shows one #0523532 gasket, the smaller one, but then calls for two in each assembly. The Service Manual only shows one gasket as well between the adapter and the tank. The surprise I got was finding that the fuel tank adapter was screwed into a mating flange that is in the tank. It is between this flange and the tank that the second mystery gasket goes. No manuals I have seen mention anything about this little threaded flange in the tank..into which the filler neck is also threaded. If I had not had the cap chain still attached, the flange would have dropped off into the tank with the filler neck still attached. This arrangement really baffles my IA as there appears to be no way to get the flange out of the tank if it becomes damaged. Appears that the tank is manufactured with the flange alread in the tank? Anyway, whoever put things together years ago did not use one of the smaller rubber gaskets between the internal tank flange and the tank...I just had one gasket between the adapter and the top of the tank...which was not doing the job. Without the second gasket installed INSIDE the tank, water was free to pool up in the moat and drain into the tank...and then fuel came out using the same route. Does anyone know why the heck the filler neck wasn't welded to the tank like later 172s? So yes, Virginia the tank does require two of the smaller rubber gaskets #0523532 and only one of the large cork gaskets #0523531. Too bad the manuals do not depict the placement of the second gasket and the strange little flange residing inside our fuel tanks

c170b53 · Post by **c170b53** » Thu Feb 12, 2004 3:30 pm

This stuff was alluded to earlier with filler neck replacement. The neck assembly would be dropped into the tank held by the chain or lockwire. The gasket will follow down the lockwire into the tank and then raise the neck assembly to position and align the gasket holes for the screws. Just out of curiousity how deep are the stakes that hold the filler neck into the fitting that resides in the tank?

wa4jr · Post by **wa4jr** » Fri Feb 13, 2004 12:11 pm

Woops! Evidently I missed the earlier discussion, but still wish Cessna had at least depicted the placement of the second internal gasket along with the internal flange and talked of it in the service manual so when someone was taking out that last screw they would be ready to catch the assembly before it fell into the tank thus requiring a "fishing trip". But then that would take all the "fun" out of the project. Regarding the stakes, I only have one in my filler neck, and it does not seem very deep. I have elected not to separate my filler neck from the internal flange as I now think all of the water entering the tank and fuel exiting the tank was taking place around the internal flange to tank area that was missing the required gasket. Also a factor in deciding to leave the neck in place is the fact that the assembly cannot be separated from the tank in order to grind the stake out and unthread the neck thus avoiding sparking a "nasty event". Someone in an earlier post said he separated his filler neck/internal threaded flange assembly from the tank before commencing the unthreading operation...he must have a different tank than I do in my '54 cause this isn't possible with my airplane. I'll just replace all the gaskets and both fuel caps and hope that is enough to keep the water out and the yummy fuel in. By the way, most of the screws came out nicely with an impact driver and machinist hammer, with only one head shearing from the screw itself. Of course it was in the forward spar where a U channel blocks access to the nutplate...so here comes the drill! Oh yes, I asked my IA about stainless vs plated for the new tank hardware...he said going stainless was the way to go. More food for thought

N170CT · Post by **N170CT** » Wed Feb 18, 2004 5:14 pm

John,

You de man. THAT was exactly the question I was feebly attempting to ask when this thread started. The Parts Manual calls for two small gaskets, but only illustrates one. Service Manual is no help either. It appears you broke the code. Sincerest thanks for the info. Bottom line.... Is it worthwhile to change all three gaskets or is it too difficult to change the one not illustrated??
Further, do you or anyone else out in 170 land have any experience utilizing a sealant (as done on Mooney wing tanks)??

Again, thanks for your time and comments.

jlwild · Post by **jlwild** » Thu Feb 19, 2004 2:07 am

I just finished replacing all three gas tank gaskets in my right wing today. It's a good thing I did. My tank did not have the "third" gasket, that is hidden inside the tank. The famous "small one" not illustrated in the Parts Catalog. Once you have the tank cover off, everything can be easily reached. Therefore, I recommend you go ahead and change out all three. You may also be missing a gasket.

It was not a difficult job once I read the forum notes on where the three gaskets were located. And, also don't forget to hang onto the gas cap chain while removing the screws.

By the way, all my screws came out easily. However, I soaked them in "mouse milk" for three days prior to removal. Only a few required a sharp rap with a rubber hammer on the screw driver to get them broken loose

Sorry, I don't have any experience on the sealant used in Mooneys.

Tomorrow I start on the left tank gaskets.

jlwild · Post by **jlwild** » Fri Feb 20, 2004 11:55 pm

Well, removed the left tank in one hour. It sure is easier after learning on the right. The suprise was finding the 3 gaskets around the filler pipe were (1) all present and (2) not leaking. In fact, they looked very good for their age.

But, UGH, the bad news was the fuel tank has two pin hole leaks. The first is in the welded tank seam where it meets the fuel gage flange. The second is in the weld where the gas line fitting attaches to the tank. Now trying to decide what to do. Hopefully they can be welded.

Anyone have experience with fuel tank welding repairs?

Other items needing TLC are broken tank cover nutplates along the forward spar and Tinnerman nutplates on the inboard rib hold the wing root fairing on.

Oh well, it's going to take some more time to get everything back together.

c170b53 · Post by **c170b53** » Sat Feb 21, 2004 9:21 pm

Its refreshing to see you atitude in addressing the problem, and understanding that these older machines require patience.

3958v · Post by **3958v** » Sun Feb 22, 2004 12:15 am

I had my ragwing tanks welded by a GOOD local shop. I also spread some Proseal that the RV guys use on the inside to seal their tanks but I put mine on the outside of the weld for some extra protection. I have put fuel in tanks but have not flown yet. So far no leaks. Some one had used proseal type material on my tanks back in 1966 when wings were last covered and it seemed to have worked so I figured it probably would not hurt and going on the outside of the tank probably would not upset the Feds too much. Bill K

wa4jr · Post by **wa4jr** » Mon Feb 23, 2004 4:21 pm

Boy these fuel tank jobs sure are fun

I said earlier that the two smaller gaskets on each tank appeared to be a rubber composition. Closer inspection reveals them to be cork that has turned black over the years. Oh, the fun part. One of the screw heads snapped off on a forward edge screw. Of course the rolled lip of the wing structure along with the tight fitment of the tank prevented any access to the screw from below....so out comes the tank. If only the service manual had said that it would be more enjoyable to put my head in a vise and tighten rather than try to extract the tank from a wing bay that is really too small

Upon opening my tank bay, I immediately noticed that the rear of my tank had been bent. I thought someone had dropped it years earlier but quickly found out that it gets bent during the extraction process. The tank bay really needs to be 1 inch larger in the fore/aft dimension. But I should thank the broken screw for requiring my tank to be removed as I found a small hairline crack on the underside of the aft portion that had been leaking fuel for a long time. The leak was not large enough to overcome evaporation and exit the wing, but there was plenty of nasty aged gum and varnish around the leak area. The tank is out now for welding and checkout. I also found both tank securing straps loose, with worn rubber bushings, and both strap screws were bent smoothly to a 20 degree angle from overtightening and/or overstressing. My right tank has also been damaged from someone using screws that were too long in securing the door catch bracket to the underside of the wing. I wonder what joys still await me in the left wing tank bay

Post by **GAHorn** » Tue Feb 24, 2004 1:43 am

It takes real talent to accomplish some jobs. Not just mediocre ability, but real talent! There's an interior shop here in Austin that does not-too-bad appearing interiors. But they've got talent that few others possess. We discovered it on a friend's airplane recently.
I mean, ...like how would you do this if it was your deliberate aim??? HOW would you/could you take a PK screw and,....using a screwdriver ...free-hand no less....run a too-long PK screw directly through a sidewall and absolutely CENTER a metal fuel line so neatly that it didn't visibly leak for several years!!?

Now that's real talent! You couldn't get a PK screw to hit a metal fuel line and not slide off to the side if you had to. But these guys did it on one attempt!
It took two years before we finally traced the fuel smell down to the doorpost/sidewall area.

Anyway, it's a good idea to replace hardware with that specified in the IPC whenever possible.

Dave Clark · Post by **Dave Clark** » Tue Feb 24, 2004 2:56 pm

George

Exactly what happened to me! When I was into painting my door jams last year I pulled the very small PK screws an earlier owner had used from the dataplate (yeah they're supposed to be rivets), and in a few minutes fuel was running out of the belly. Panic time for a few seconds until I found where it was coming from and put a screw back in it to stop the leak. Of course I changed the line. Same thing though, three years of that mysterious, occasional gas smell that I could not find suddenly went away!

wa4jr · Post by **wa4jr** » Fri Mar 05, 2004 7:12 pm

HELP

The local shops that used to weld fuel tanks have stopped becuase of insurance liability reasons. My IA has found only one shop, in Michingan I believe, that will weld the tiny hairline crack in my right tank, and then do UV and pressure tests. Price is quoted at anywhere from $250 to $1000 plus shipping, which will be considerable given the size of the tank

My initial thought is to get a salvage tank from another aircraft, but then I am told that it will still have to be inspected and the end price could be the same or more than if I welded my present tank. I've also thought about capping off the right fuel line, putting the tank cover back on, and just flying with one tank

But seriosly, this is a simple repair weld on a dirt simple aluminum tank and a $1000 tank repair on a $35000 airplane scares the hell out of me...not to mention makes me madder than you know what! Can someone who has run into this problem before please advise me on the best course of action