Fuel drain threads

[Maineboy]

I'm wondering if anyone has run into this problem. The threads are stripped in my wing tank where the fuel drain screws in. They are not totally gone but close. Is there a repair short of replacing the tank. Do you think a Heli-coil would work? Would this be legal??
Thanks

[N2865C]

I had the same problem on my 120. My AI had some fuel proof bonding sealant that he put on the threads. Mine felt fairly loose, but it would be a judgment call depending on how far the threads are gone. I can find out what it was if you want me to check. The other option he gave me was to pull the tanks and have them welded.
jc

[GAHorn]

Are you certain you are using the correct Curtis Drain valve? They make lots that look the same, but the threads are different. The correct PN for a 170 is: CAV-170 available from Spruce, 877-477-7823. (Threads are 7/16-20)

[Maineboy]

yes, I got the right valve, but now that you mention it, that's probably what happened to the threads. Someone probably tried to screw the wrong one in. I will check the one I removed . 7/16x20 should be the correct one.
jc, thanks but I don't think there is enough threads left for that. The valve just keeps spinning around.

[zero.one.victor]

Are you certain you are using the correct Curtis Drain valve? They make lots that look the same, but the threads are different. The correct PN for a 170 is: CAV-170 available from Spruce, 877-477-7823. (Threads are 7/16-20)

Ain't necesarily true,George. My ragwing has two drains at the LH wing (added tank),one at the RH wing,and one at the gascolator. I have two CAV-170 drains ( 7/16"-20) and two CAV-110 drains (1/8"NPT). As I recall,the CAV-170's are both at the LH wing tanks. Don't know why they're not all the same,but there you are......So be careful when replacing the drains,check the number before you buy and especially before you start twisting them in! Beware, "CAV110" can look alot like "CAV170",especially when that's what you expect to see.

Eric

[zero.one.victor]

Another thought on the quick drains: when they start leaking they can be removed & new itty-bitty O-rings installed. Have a plug or your wife's thumb handy to plug the hole while you're changing o-rings,this ain't a one-handed job! It's helpful to wear a short-sleeve shirt & tie rags around your wrists when doing this job,to avoid an armpit-full of gas.
However,if the top of the quick-drain (where the snap-ring retainer is, that holds the whole thing together) is corroded,just buy new ones. You don't want it failing in-flight & causing the fuel tanks to become filled with air! They will tend to corrode due to being situated at the (watery) low point of the tank or system.
You can re-O-ring the old rotten drains & keep them in the plane for emergency use,or for plugging the hole when you have to re-O-ring the new ones in a few years.

Eric

[zero.one.victor]

Are you certain you are using the correct Curtis Drain valve? They make lots that look the same, but the threads are different. The correct PN for a 170 is: CAV-170 available from Spruce, 877-477-7823. (Threads are 7/16-20)

Just looked at the quick-drains in the Chief catalog. George,those p/n's you call out are for Saf-Air drains. Curtis drains appear to be the type with a T-handle sort of arrangement & use a different set of p/n's. For example,the equivalent to a Saf-Air CAV110 (1/8" NPT) would be a Curtis CCA 1550. I don't even see a Curtis drain equivalent to a CAV 170 listed (7/16"-20 thread).

Eric

[Curtis Brown]

Maineboy,
I had the same problem. I used the heli-coil kit to fix it. No problems for two years now.
Curtis

[Maineboy]

Thank you, I've heard from a couple people that a heli-coil will work. I'm going to give it a try.

[GAHorn]

Sorry about the confusion...I used "curtis" in the generic sense. (Sorta like making a "Xerox" copy.) But since the PN CAV-170 can only apply to the Saf-Air valve it shouldn't have caused anyone any difficulty.
What makes you sure your airplane is a "standard" airplane, Eric? My 170 ragwing IPC only shows one, obsolete, genuine Curtis valve. Is it just possible someone has substituted non-standard parts on your airplane?

[zero.one.victor]

I never used the word "standard",George. I merely commented that your statement "the correct p/n for a 170 is CAV-170" ain't necesarily true. I figure "correct" as meaning the one that fits. I figure "standard" as meaning standard. I'm not at all sure my ragwing is a "standard" 170,in fact I'm sure it's not. A bunch of 337's,logbook entries,& "incorrect" parts will bear that out. Like I went on to say,I just wanted to emphasize that people should check out the part they will be replacing carefully before they order a new part based on the "correct" part number out of the IPC or wherever. I've screwed up by doing just that on more than one occasion.
FWIW,I ust took a quick look at my IPC. I don't see any drain valves at the tanks at all. Now can that be right? I do see where they call out three different possible drain valve p/n's,at two locations (both at or adjacent to the fuel strainer):"CPP-100-2 drain,fuel" "K9000A-1 drain cock ,fuel strainer" and "K8000A-1 drain cock,fuel strainer (alternate)".
Now regarding the Curtis versus Saf Air valves: lotsa times the counterperson or order-taker you have to deal with might not know that the CAV170 is a SafAir number. They might just look under Curtis,then tell you "nope,we don't sell the Curtis CAV170's". Often they're the lowest-paid least experienced person there. I was just trying to save someone some trouble. Guess I should just keep my mouth shut.
I'll leave it to you to point out mistakes,since you obviously never make any.

Eric

[GAHorn]

I never used the word "standard",George. I merely commented that your statement "the correct p/n for a 170 is CAV-170" ain't necesarily true. I figure "correct" as meaning the one that fits. I figure "standard" as meaning standard. I'm not at all sure my ragwing is a "standard" 170,in fact I'm sure it's not. A bunch of 337's,logbook entries,& "incorrect" parts will bear that out. Like I went on to say,I just wanted to emphasize that people should check out the part they will be replacing carefully before they order a new part based on the "correct" part number out of the IPC or wherever. I've screwed up by doing just that on more than one occasion.
FWIW,I ust took a quick look at my IPC. I don't see any drain valves at the tanks at all. Now can that be right? I do see where they call out three different possible drain valve p/n's,at two locations (both at or adjacent to the fuel strainer):"CPP-100-2 drain,fuel" "K9000A-1 drain cock ,fuel strainer" and "K8000A-1 drain cock,fuel strainer (alternate)".
Now regarding the Curtis versus Saf Air valves: lotsa times the counterperson or order-taker you have to deal with might not know that the CAV170 is a SafAir number. They might just look under Curtis,then tell you "nope,we don't sell the Curtis CAV170's". Often they're the lowest-paid least experienced person there. I was just trying to save someone some trouble. Guess I should just keep my mouth shut.
I'll leave it to you to point out mistakes,since you obviously never make any.

Eric

Firstly, I politely apologized for the "mispoken" Curtis name-brand when I "corrected' myself. I didn't insult you, Eric.
I never said you used the word "standard'. I used that word to try to figure out why your airplane should be utilised as an example to troubleshoot the problems of others,...especially since you are cognizant of the lack of conformity of your airplane to the documentation.
I hardly think it unreasonable to supply the factory-specified part number and referring to it as the "correct" one!

Of course, I should first have determined that Maineboy's airplane is an A or B model before I jumped out there with the CAV-170 pn. Since the ragwing IPC doesn't show wing drains I made the somewhat hasty conclusion a CAV-170 was "correct." But as has been pointed out, it might be a ragwing that doesn't conform to the IPC.

[Tom Downey]

I'm wondering if anyone has run into this problem. The threads are stripped in my wing tank where the fuel drain screws in. They are not totally gone but close. Is there a repair short of replacing the tank. Do you think a Heli-coil would work? Would this be legal??
Thanks

If your 7/16 threaded drains are stripped out, re-thread by using the 1/8 NPT and switch drains.

Heli coils will leak after a while, the new pipe thread won't.

[flyguy]

I agree with Tom. If there is enough "meat" change to the 1/8NPT. If you had straight 7/16x20 and still have material, go for the 1/8NPT mod. Use "fuel-resistant" RTV (lightly applied!) on squeaky clean (acetone or equivalent) mating parts. CAUTION! A 1/8NPT tap can eat your lunch! Be careful to count threads. If you run the tap in too far the mating surfaces wll not seal correctly before you come to the last threads on the drain. Not far enough - - the possibility of stripping out again or the failure to seal properly.

There is a possibility (worse case) that you had NPT already and now have to helicoil anyway. First choice if there is enough material: do the 7/16 straight thread "Heli-coil" repair. They do make "Heli-coil" inserts for 1/8 NPT if you are short of "meat". As it will be a tapered hole you must be super careful to "count threads" to make sure you can install the insert deep enough but not too deep.

Here is the "Tip of the Day" to keep the "Heli-Coil" (or 1/8NPT also) repair from leaking. Get one of two spot-face tools - one large enough to renew the whole face of the "boss" if you are going to 1/8NPT. The other one just large enough to give you a new clean area for seating the "O" ring under the flange of the "drain". Machine tool suppliers will be the source for those spot facers. Make sure that the small one has a .060 radius on the cutting edge with a .375 pilot to center the tool as you restore this surface. You will be doing the machining with a hand powered drill motor so use one with lots of low speed control and just remove enough to get the surface acceptable for the "O-ring". Now super clean (acetone) all surfaces and coat* the "Heli-coil" (or 1/8NPT CPP100-2 if this is the repair of choice) with fuel resistant RTV (silicone sealant) just prior to installation. Wipe excess sealant from inside of your threaded hole and screw the drain in while silicone sealant is still maleable. Seat the "helicoil" one/half thread below the surface.

TWO CAUTIONS! 1. Carefully retrieve the "break-away tang of the heli-coil insert so it won't be left to get into thepassageway of the fuel-drain! 2. * Lightly coat! You don't want a big gob of sealant in the passageway or on top of the fuel-drain.

[GAHorn]

BIG BIG BIG CAUTION: I'm sure everyone knows that Ol' GAR was talking about an AIR DRILL or a hand-drill .....NOT an ELECTRIC DRILL...
when working on a fuel tank.
Remember also that steel tools like taps and drills generate heat and can make sparks. It won't hurt to flood the tank with CO-2 (best) or Nitrogen from a compressed gas bottle during this work.

Permatex #1 will "set" a helicoil yet be easily cleaned out via thread-chaser or die later. Yet another product specifically designed for this purpose is BakerSeal, PN 09-00346, $5.50 from Aircraft Spruce 877-477-7823.