The International Cessna^® 170 Association

has anyone seen this before. the plane has no other corrosion issues and has approx 5500 hrs. if the fuel tanks wouldnt have been leaking this might not have veen seen for many more years.

That looks like very serious exfoliation. I saw that once before on the front spar of an A model down in San Carlos,CA. The owner, an A&P, replaced the front spars. One helluva big job.

Wow, makes me want to pull the tanks out of 81D and have a peek.

Sorry to see this but, please take lots of photos of the repair work.

This is EXACTLY the area and type of corrosion which we discussed and demonstrated at the Benton Harbor convention seminar. Del Lehmann supplied me with the spar-extrusion he discovered on a 170A with the same defect.

It was decided that it would be a good idea, perhaps while regularly refueling even, to closely inspect the rivet line at the spar immediatly forward of the fuel tanks for bulging, buckling, or other evidence of the corrosion "pushing" up on the skins between the rivets as the result of "swelling" from intergranular corrosion.

I still have that extrusion and will bring it to Bardstown, Kentucky next summer. We will inspect all the airplanes that make the convention as part of the service-seminar being introduced.

How hard is it to pull the covers off the fuel tanks and have a look around?
It seems like it's just a bunch of structural screws and the piece comes off. Any trick to it?
At that point, you could at see quite a bit of the area and soak everything with some corrosion inhibitor.

Mine has pretty shinny screws up there. I'd like to think they're not seized up and removal would be straight forward.

David, it is, in theory, a simple task. However most of those 50+ screws have been in there for 50+ years! Be prepared to find some that you may have to drill out and there are two different lengths of them. Not a short morning job.

In my case, it might be a lot easier.
The plane was repainted 4 or 5 years ago and the hardware up there looks to be new stainless. (They are structural screws tho) If its anything like the wing tip fasteners, they will come off pretty easy.

Will I be able to see enough with the cover off to judge the over all condition of things? Or should I pull the tanks out to see anything important?

Next question: when re-installing the screws, is it a good idea to put some anti-seize or LPS2 on the threads?

We have two very capable Members here (among others) who should probably speak on this topic: Jim McIntosh (c170b53) and Del Lehman (wingnut). Jim is "Mr. Corrosion" in my book, and Del is "Mr. Metalsmith". They are the fellows who contributed so much to the study of the corroded spar in Benton Harbor.
"Wildman" (Jim Wildharber, aka jwild) also developed a nice PowerPoint presentation on fuel tank R&R which he presented at the Tehachapi convention which MIles hosted. It may be time to corner him and c170b53/wingnut into another episode at Bardstown, and I'll work on the coercion efforts.

David, as George mentioned, former 170 president Jim Wildharber put together an excellant program on how to remove those fuel tanks. There is probably some threads on this forum on that subject. I followed his guide, talked to him and still had a h_ _ _ of a time getting both of them out and then back in. As I have said previously, Cessna hung the fuel tanks and fuel valve from the roof and built the airplane around them Tough job, but it can be done.

gahorn wrote:We have two very capable Members here (among others) who should probably speak on this topic: Jim McIntosh (c170b53) and Del Lehman (wingnut). Jim is "Mr. Corrosion" in my book, and Del is "Mr. Metalsmith". They are the fellows who contributed so much to the study of the corroded spar in Benton Harbor.
"Wildman" (Jim Wildharber, aka jwild) also developed a nice PowerPoint presentation on fuel tank R&R which he presented at the Tehachapi convention which MIles hosted. It may be time to corner him and c170b53/wingnut into another episode at Bardstown, and I'll work on the coercion efforts.

That alone would make the trip to Bardstown worth it!
If any of the coercion efforts involve alcohol, I'll pitch in for the tab

In the mean time, I might still try and take a peek under the cover.

David, send me a reminder end of November and I will forward the power point tank removal info. I am currently in New Haven, CT visiting grandchildren and don't have access to my files. Also since George open the topic, I will be happy to give the Power point presentation again at the Bardstown convention. The Whitson family, Bardstown Convention Hosts, are planning on lots of flying events and maintenance discussions.

Word of caution on taking a peek, check your parts manual. On the 170 B there is a gasket under the tank cover you will most likely damage during the removal process. Also, somewhere on the forum are pictures of the tank gaskets. I can't find it right now but perhaps someone else can point you to them.

I stated in another blog about wooden blocks being screwed to the spars (forward and aft) and finding corrosion under them but I say that we had to replace about 130 rivets on the spars has they had to start to crumble. Yes Crumble.Given a light tap with a hammer and screw driver the heads fell off. this was on both wings .Especially from the fuel tank area to the strut attach point . I have just finished the job. notified Cessna and they sent back a program called SIDS.How airplanes are getting old like the rest of us.

David, I removed the tanks on my first 170. Had heard horror stories and believe they could be true. But it was a lot easier that I expected because I was prepared for what I found.

First there is a LOT of screws. Even if the all come out easy you will want some type of motorized screw driver to save you wrists. Of course us all precautions not to strip the head of the screw. Loosen the screw by hand.

Have GOOD screw bits. Snap On sells bits with little teeth in them to bit the inside of the screw. A worn bit means stripped screws.

Have a good rust penetrant like PB Blaster or Krol. Use it now so you can get the screws out next month.

Learn good screw removal technique. Clean the dirt out of the screw head so the good bit will seat. If the screw does not immediately turn out stop. Try lightly taping on just a screw bit place in the screw head to break the screw loose. Try TIGHTENING the screw just a bit. Once the screw moves put more rust penetrant on it. If is starts getting tight coming out stop. Put it back in, put penetrant on it. Slowly turn it back out a bit and repeat until it is out.

If the screw head strips out and you can not get a good bit stop. Get a Dremel tool with a cut off wheel and CAREFULLY protecting the paint, grind a slot in the screw head. The use the largest good fitting flat tip screw driver. Worse case the screw head breaks off. Don't drill it out UNTIL you have the the rest of the screws out and the skin off so you can see what your drilling into. There may be a good chance you don't have to drill at all but the screw but you can get a hold of it on the underside and spin it out by spinning it into the tank area.

The tank is a tight fit and getting it out and in can try your patients. Of course it needs to be empty. And you need to remove the drain valve from the bottom as well as not only disconnect the supply line but remove the rubber hoses from the vent lines. You will also want to remove the fuel tank gauge. The fit is that tight the rubber hoses and gauge cause fits.

Plan on a good days work to remove and reinstall one tank assuming you make no repairs or just to remove both tanks. Be prepared to want to clean and paint the tank bay and replace all the gaskets and rubbers in there. This is also and excellent time to replace all the gaskets in the tank inlet and under the fuel sender.

My wings were removed (one in a accident) about 11 years ago and they were totally disassembled and rebuilt removing some corroded parts and skins so I'm not so worried about this but one of these days I have to remove my tanks to install the door stops my partner decided not to reinstall. Big mistake. (So George while it LOOKs like a RAT plane it's condition is better known than most. )

David, Bruce has given you some excellant pointers/techniques that will help with your project. I also had a few screws that required using a Dremel to cut a slot into the head of a screw that stripped. I purchased a NEW long handled screwdriver for my project which helped a bunch. I did have one that snapped off and after removal of the fuel tank cover, I soaked the remaining shank with mouse milk and it screwed out into the fuel tank bay as Bruce mentioned. One other technique I used, which seemed to help, was after cleaning out the Phillips screw head of dirt/paint, etc., was to dip the screwdriver bit into some valve lapping compound. That can make the screwdriver bit bite a bit more. One of the more difficult chores on my plane was removing the 50+ year old rubber hoses. I had to litterly cut them with a large kitchen knife as we couldn't get them out any other way. Put a jar on the wing and everytime you utter a curse word put a dollar in the jar. By the time you are finished you can enjoy some brewskis Give us a report on how it goes and what you find in those fuel tank bays

Bruce, I'M not the one to critique anyone's "ratplane" aspirations...
I was only acknowledging the prided category.