Wing sump repair

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mmoyer777
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Wing sump repair

Post by mmoyer777 »

The threads are stripped for my wing sump. A&P is telling me I need to cut the wing, remove the tank for repair, then replace and patch the fabric. For some reason, the sump is smaller than the SAF-AIR called out (CAV-160). Can the tank drain be tapped to fit the CAV-160? Can Loctite Aviation Gasket Sealant be used?
Thanks in advance.
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Re: Wing sump repair

Post by 6277 »

As I understand, some tanks outlets had coarse threads, some had fine threads. My plane had SafeAir valves when I got it and one side leaked because the threads were damaged. I cleaned the threads with a tap and changed over to Curtis valves which have a longer thread area and therefore more sealing area. I also used some fuel lube on the threads. It's been dry ever since.
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Re: Wing sump repair

Post by 6643 »

It's my recollection some tanks have pipe (tapered) threads and others have straight threads. the difference was early or late manufacture. I forget which was which, but I'm thinking early was tapered. My plane has one of each...
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Re: Wing sump repair

Post by 6468 »

I just finished this exact repair on my friends 140 last week. Used a 7/16 HELI-COIL & the Curtis straight thread. Stopped the insert when 1/32 recessed. Also take a file to the insert to remove the coils sharp trailing end before screwing into place. The straight Curtis valve uses an O ring to affect a seal. Go slow with the drilling (work your way up in drill size). I put grease on the drill bits & ran a vacuum sweeper when re-sizing the hole, then used a Q-tip to carefully clean out any debris. Worked great, just take your time. A specific drill size, tap & breakoff tool are needed and should be included in the Heli-coil "kit". Your mechanic probably has on of these kits laying around his shop, if not they easy to find. good luck Jim S
mmoyer777
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Re: Wing sump repair

Post by mmoyer777 »

Thanks for all the advice!
I might be able to get away with cleaning the threads with a tap and using a Curtis valve, but I will need to figure out how long a valve to use. The SAF-AIR CAV-170 stem with threads look to be about 5/16" long and there is definitely a metal stop preventing the sump from going too far in the tank. The SAF-AIR CAV-160's stem is about a 1/16" longer, but is also about 1/16" thicker in diameter and a tapered thread.
The CAV-160 is what Spruce calls out for the C140 and the smaller CAV-170 just spins. But itlooks like there is enough metal to drill and Tap the sump hole with a 1/4" NPT Tap. Maybe I can get away without using a HELI-COIL. Any thoughts?
I'd also like to use Loctite 567 on the threads.

Thanks for the grease on the drill, go slow, and Q-tip tips!
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Re: Wing sump repair

Post by 6643 »

mmoyer777 wrote: Thu Jul 14, 2022 5:38 pmI'd also like to use Loctite 567 on the threads.
Why? Use "Fuel-lub" on the tapered threads. Tapered threads don't require any locking device. If you're using a straight thread, the o-ring provides the seal and it should be safetied to a hole in the aluminum skin under the fabric surrounding the hole for the drain.

Drill size for a 1/4" NTP tap is 7/16", so a stripped out 7/16" thread should be just about perfect.
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Re: Wing sump repair

Post by mmoyer777 »

Thank you again for the reply!
I know SAF-AIR recommends using Sealube and I have Parker - OLUBE884-2 - 884 O-Lube O-Ring Lubricant. But there is a study by Oasis; "Best Practice for NPT Thread Sealing" (https://www.oasisngv.com/vdb/document/1179) that recommends Loctite 567.
Also, there were no safeties on either wing nor are there holes in the CAV-160 (w/NPT) for safeties. I didn't think about running safeties to the aluminum skin. But I still have the issue of no hole in the CAV-160 for a safetie.

I'm new to aircraft ownership and comments are greatly appreciated!
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Re: Wing sump repair

Post by 6643 »

You only have to safetie the ones with straight threads.
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