The International Cessna^® 170 Association

Hey guys doing my annual yesterday and decided to change out the leaking fuel drain at the left wing root. Well came out easy, went to put the new one in and the threads are stripped ( if my old student Jim McIntosh is reading this - no I did not strip them, they were already stripped!!!!) So what options do I have guys?

We pulled the fuel tank to get at it better. The mechanic and myself are kinda scratching our heads.Some ideas........cut a portion off and retap the drain pipe? or take/cut out the old drain pipe and weld a new one in - if it is even possible to get the drain pipe part?

Of course a guy could get a new tank, that would only be about a gazzillion dollars I'm sure!

Any help would be appreciated!
Regards, Barry Gold

Would a Helicoil insert work?

I have repaired them using a helicoil and I have seen an instance where someone had bored and tapped it for a tapered pipe thread. The pipe thread job was a sloppy one and there was a notch cut in the door so that it would clear the valve when opened or closed. It probably would have worked if it had been threaded deeper.

We discussed using a helicoil as well. I think that might be a first option prior to cutting it unless someone else had some ideas. Sure appreciate the input guys!
Barry.

I'd Helicoil it but I'd bed the insert in with Devcon (or the NAPA equivalent JB Weld) to prevent any leakage around the threads

then install the drain with teflon pipe sealant or similar

I know how you feel Barry, I've got one that sometimes will leak and in my case it won't be coming out in one piece. Yes folks Barry Gold taught me to fly so its possible that he can do anything. We both work for the same company, Barry is an above the wing position (767 pilot). My employer refers to my position (aircraft mechanic, sometimes technical instructor) as below the wing and as I like to add, slightly to the rear of the airframe. I'll look into making faces at your machine my next set of days off.

Helicoil it. You do not need to use any sealent, jb weld, or anyother glue. The O-Ring on the valve seats agains the chamfer around the base of the tank pipe. (Make sense?) It should be 7/16" -20 NF threads if you are using the standard CAV-170 valve.

If I was to use a sealant I'd use Pro Seal. The sealant, if the correct sealant can't hurt. Not sure the o- ring will b big enough to seal bot the valve and the helicoil but it might be.

Barry,
How did you resolve this? I have the same problem. I am thinking about machining a new drain tube with the same O.D. and I.D. and having it welded on to the tank by a certified aerospace welding shop. The other option is helicoil, which I would try first. I think a Viton O-ring would seal it.

OBTW: I learned a trick from an old fart mechanic. Before trying to remove any fitting from any metal first use a tightening effort until the fitting turns a slight amount. Then turn in the proper direction for removal. Since I've been using this technique I've never stripped any threads.

Since this topic/thread has resurrected... I'd advise against EVER using Teflon tape in any fuel system component.

Teflon tape will shred and release particles inside the fuel system where it can clog carb passages, etc..

Heating the fitting threads first with hot air will expand them and perhaps release the drain (or bolt, or whatever is male.) Keep the drain cool with ice against it inside a rag.

I'd suggest helicoil if at all possible, or drilling/re-tapping, even to the point of going to the next size UP and using a different drain valve.

Barry, George is right on with his suggestion of using a helicoil as opposed to having to remove your fuel tank to have someone weld in a new fitting. At least I would give it a shot before getting into the fuel tank removal project.

If you decide to do the tank removal since your tanks have likely been in the plane without being removed in 62 yrs I highly recommend getting a copy of Jim Wildharber's step-by-step procedure to accomplish that BEAR of a job. Jim gave us a presentation at the Tehachapi, CA convention and I believe it is also available on this forum. Someone can probably tell you where to find it. It sure helped me when I removed both of my tanks several yrs ago. Good luck!

I had that problem years ago and took the tank to Delair in Porterville. Chris cut the old pipe out and welded a new one in. He has a a large jig to hold the tank while he welds it and if I remember pressurizes the tank with inert gas during the process. They may have serviceable drain pipes available. I think the one I got was new. Hasn't leaked since.

gahorn wrote: Teflon tape will shred and release particles inside the fuel system where it can clog carb passages, etc..

I don't ust teflon tape either, but any particle that will pass thru the gascolator colessing screen will pass thru the carb.

When I repair one of these, I over size the stripped hole to the next pipe thread, then plug it with a pipe plug, grind flush, then drill and thread back to standard.

It's like making a threaded bushing.