" Price is quoted at anywhere from $250 to $1000 plus shipping"
HOLEY MOLEY
Too bad you're on the right side. Out here on the Left side we have Jim Foreman near the SEATAC airport who does excellent work and is approved. Don't have his number handy but maybe Bela or someone else can get it or do an information call to the operator for Foremans Welding, I'm thinking in Federal Way, WA.
John,how about an "unauthorized" repair at a local welding shop? I won't tell if you don't......
Back in my motorcycle days,I had a gas tank crack welded up. The welder just sloshed it out real well with soapy water first. Guess that was to make sure the gas was eliminated. From what I remember,the real anal welders purged the tanks with nitrogen before/during welding.
I sure have thought about a good application of JB weld since it is not a structural repair, but with my luck I'd leave a finger print in the stuff and the FAA would be right there to help me And Eric, I did think of using one of the race car shops around this area that work with high tech alloys...an aluminumn tank would be child's play for them. When I asked my IA about this possibility, he then asked me what the FAA approval data would be for the repair So there you have the answer on using any one of the fine race car shops. Common sense be damned here. Problem is, as you can see, the cat is out of the bag. Had I pulled this tank out back in my hangar and found the leak...I would have gone to the race car shop, had it properly welded, and then returned it to the bay. Since the crack is on the underside, no IA would find the repair unless the tank were pulled again for some reason. My IA is the only one on the field, and my airplane is down for this problem, and he is also the one that is doing my annual next month...soooooo...I am like a little rodent in a corner with the FAA on one side and my IA on the other. Seems there is no escape other than to send my tank to a NASA shop and prepare my backside for some pain! One I fly off this little field and hangar at my airpark location, I'll have much more freedom to make common sense repairs in my own backyard. I will follow up on the tip from the fella in PA though, before sending my tank and wallet to the space shuttle repair depot for X-ray gamma ray atomic particle bombardment UV scanning and pressure testing....oh and yes...a simple weld repair on the hairline crack
John, I'd find another IA who would agree to "supervise" the weld repair and reinstall the tank. This is not a structural item.
Try locating your local EAA chapter and find a member there who does TIG welding to fix it for you. I'll be they also have an IA who'll sign it off for you.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
Good news, both my gas tanks are back from the repair shop. The two small pin hole leaks were T.I.G. weld repaired and both tanks pressure checked for any other leaks. The great news is the local I.A. repair shop only charged me $135 for materials and labor. That included pickup and return of the tanks.
SAFETY CHECK NOTICE..... While the tanks were out, the fuel lines from the tanks, leading into the fuselage, were carefully checked for possible leaks. The BAD NEWS is the fuel line from the left tank, covered by a protective rubber tube, was over 50% worn thru by rubbing on the fuselage frame. The only way I found the damage was by removing the rubber tube. The rubber tube was masking the wear point. My IA thought the gas line was very close to the point of breaking. The results, in flight, would not have been fun. SUGGEST, everyone check this potential wear point carefully during next annual.
Jim Wildharber, Kennesaw, GA
Past President TIC170A (2010-12) and Georgia Area Representative
'55 170B, N3415D, SN:26958, O-300D; People's Choice '06 Kelowna, B.C., Best Modified '07 Galveston, TX, Best Modified '08 Branson, MO.
Having recently done this project, we learned that previous assemblies were done wrong. The small gasket goes inside the tank, yes. Do not install an additional one on the outside top. This can cause a dimpling of the thin filler neck flange at the screw holes which cause leakage. Check and make sure any dimpling is removed before installing. For improved water sealing, we added "Pro-Seal", not real name, to the screws and around filler neck to flange opening. It's a two part gas resistant product that stays flexible. I can get you the real product name if you like. My IA retained the $22 can I bought from Glacier Aircraft Parts in Palmer. Good Luck.
So even though the parts manual calls for four smaller gaskets per aircraft...two per tank...only one should be fitted to the internal tank flange? What then is to seal the filler neck flange-to-top of tank joint against water intrusion? Proseal on the screw threads will take care of water migrating into the tank via the screw threads, but the water will still be able to enter the tank bay via the gasketless flange fitting...which I don't guess is too bad, but I'd rather have the tank bay dry.
My right tank is back from Tradewinds Aviation in Florida. Did a good job, issued an 8130 form to make my IA happy, and charged me $400 to weld up a small corrosion hole. I told my wife that with this repair, I can see the end of my days owning an FAA certificated aircraft are numbered. I love the lines of the 170, but she is horribly underpowered for a four place family aircraft and the expense and fuss of adhering to all the FAA paperwork and not being able to do my own MX work is real drag. I'm seriously looking at starting a Bearhawk project in the next couple of years...so the 170B I thought I would own until I kick the bucket may be up for sale as soon as the Bearhawk nears completion. Thanks FAA
Your right. Two gaskets, but one is large, and one is small according to the Cessna parts manual I saw at the supplier. One small gasket inside makes a perfect seal for the flange to the inside of the tank, and the larger one seals the top skin and the recessed ring. As I said before, the addition of another small gasket outside between the tank and the recessed ring accomplishes nothing in water sealing and can cause the ring to dimple if over tightened. Besides, there's lots of space between the ring and filler neck that a small upper gasket won't seal. I think we all get use to seeing gaskets sealing from the outside rather than inside, but it works especially well in this situation since it is sandwiched against the thick flange inside and two thicknesses of thin metal from above. A better design would have been a thicker securing ring in the first place, but weight, weight, weight.
Hummm...unless I misread my IPC, it calls for 2 of the small gaskets and 1 large gasket per tank. I went back together with one small gasket and above and one below the tank. The small rubber washers that go under each of the 6 filler adapter screws prevent overtorque and damage to the adapter. The screws cannot be tightened very much at all or the rubber washers will squish out and be useless. I also used Permatex #2 on the threads to seal that route for water ingestion. Time will tell if everthing works well, but I am looking foward to not having to wipe down my airplane from wing to tail after every flight
First, my friendly A&P/IA and I (just A&P) did both tanks on my 56 170B in one day...concurrent with the annual. Observations: The tank panel screws were extremely difficult to remove, but we were prepared with the "old mans" tool from Brown Tool as some very astute folks recommended in this forum. Still broke a total of six screws, but were able to remove them. As others have found on their aircraft, mine had only two cork gaskets (one small & one large) per tank installed. We installed three when reassembling the filler neck. But there were NO small rubber gaskets??? on the filler neck screws on either tank. I know the Parts Manual calls for them, but none were there. Anybody have a source for those small gaskets/washers??? By the way, my humblest thanks for all the suggestions offered by our 170 experts.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
OK, just ordered my tank gaskets for both tanks (4 small #0523532 and 2 large #0523531). Am going out to the hanger to start lubricating the screws and picking the paint out of the screw heads, but after looking at the IPC I can't tell - does the tank cover assembly (Item #42 on figure 7) need to also come off to replace these gaskets?
Can the job be done without removing that cover?
And if it CAN be done without removal of the tank cover, is there a reason to still remove it (easier, check on condition, etc.)?
Kyle
54 B N1932C
57 BMW Isetta
Best original 170B - Dearborn, MI 2005
Cessna® is a registered trademark of Textron Aviation, Inc. The International Cessna® 170 Association is an independent owners/operators association dedicated to C170 aircraft and early O-300-powered C172s. We are not affiliated with Cessna® or Textron Aviation, Inc. in any way.
And Eric, I did think of using one of the race car shops around this area that work with high tech alloys...an aluminumn tank would be child's play for them. When I asked my IA about this possibility, he then asked me what the FAA approval data would be for the repair 
So there you have the answer on using any one of the fine race car shops. Common sense be damned here. Problem is, as you can see, the cat is out of the bag. Had I pulled this tank out back in my hangar and found the leak...I would have gone to the race car shop, had it properly welded, and then returned it to the bay. Since the crack is on the underside, no IA would find the repair unless the tank were pulled again for some reason. My IA is the only one on the field, and my airplane is down for this problem, and he is also the one that is doing my annual next month...soooooo...I am like a little rodent in a corner with the FAA on one side and my IA on the other. Seems there is no escape other than to send my tank to a NASA shop and prepare my backside for some pain! One I fly off this little field and hangar at my airpark location, I'll have much more freedom to make common sense repairs in my own backyard. I will follow up on the tip from the fella in PA though, before sending my tank and wallet to the space shuttle repair depot for X-ray gamma ray atomic particle bombardment UV scanning and pressure testing....oh and yes...a simple weld repair on the hairline crack 
While the tanks were out, the fuel lines from the tanks, leading into the fuselage, were carefully checked for possible leaks. The BAD NEWS is the fuel line from the left tank, covered by a protective rubber tube, was over 50% worn thru by rubbing on the fuselage frame. The only way I found the damage was by removing the rubber tube. The rubber tube was masking the wear point. My IA thought the gas line was very close to the point of breaking. The results, in flight, would not have been fun. SUGGEST, everyone check this potential wear point carefully during next annual.
