The International Cessna 170 Association

Advice needed! Into month 7 of my first annual of a '52 170B. Searched forums and have not found any discussions re what to do when you discover that the quick drain valve installed in your wing tank has standard threads vs pipe threads. We removed the quick drain in order to flush the tanks because we were getting dirt into the sediment bowl. The quick drain was not leaking but out caution, my IA wanted to drain the tank and slosh new fuel and drain it through the wing tank drain. We removed the quick drain only to learn that it had standard threads vs pipe threads. Now of course, we are concerned that reinstalling it may screw up the threads and the same concern about installing a new quick drain with the proper threads. Any experience from others who have run into this problem would be appreciated.

Mike,
Your '52 tanks should use drain valves with 7/16-20 threads. The '48 apparently uses valves with NPT threads.

n2582d wrote:Mike,
Your '52 tanks should use drain valves with 7/16-20 threads. The '48 apparently uses valves with NPT threads.

Correct. I suggest Mike that you obtain an IPC and ask your IA why he is inspecting airplanes for which he hasn’t got correct maintenance data. (politely)

The IPC for a 170-B shows an AN814-4BL plug in that drain which is a 7/16-20 threaded plug. The quick drains are minor alterations.
Here’s where you can buy the SAF-AIR CAV-170:
https://www.aircraftspruce.com/catalog/ ... key=139318

Thank you! Thank you! You have saved me from a near "maintenance catastrophe". We had replaced the quick drain in the right tank because it was leaking. The threads were NPT. Consequently, when we removed the quick drain from the left tank, my IA noticed that it had straight threads (7/16 x 20) and concluded that someone had forced the quick drain into an NPT threaded fitting and therefore we needed to find a solution short of removing the tank (which was to be the last option). Upon further examination. I learned that the nipple on the right tank was recessed much further than that on the left tank. Surprise! Somewhere along the past 70 years, the right tank had been replaced and the nipple had NPT threads. Had you not answered my question so quickly, who knows what trouble we would have gotten into. Thanks again. MK

1moretw wrote:Thank you! Thank you! You have saved me from a near "maintenance catastrophe". We had replaced the quick drain in the right tank because it was leaking. The threads were NPT. Consequently, when we removed the quick drain from the left tank, my IA noticed that it had straight threads (7/16 x 20) and concluded that someone had forced the quick drain into an NPT threaded fitting and therefore we needed to find a solution short of removing the tank (which was to be the last option). Upon further examination. I learned that the nipple on the right tank was recessed much further than that on the left tank. Surprise! Somewhere along the past 70 years, the right tank had been replaced and the nipple had NPT threads. Had you not answered my question so quickly, who knows what trouble we would have gotten into. Thanks again. MK

WHOOO-HOOO! …. 170 Assoc’n Membership Dues to the Rescue..!! (again…)

Not sure how or why, but my 55 takes a CAV160 in the right tank. -Guessing the tank was replaced or modified at some point or maybe they screwed up on the assembly line.

Point is, you can’t always go by the book.

Vertical wrote:Point is, you can’t always go by the book.

A long time ago I might have had this opinion. When I've come across a situation where the IPC and what my 170s, Cub and now Vagabond had installed, it has never turned out to be "because the factory used the wrong part". Its always was because somewhere along the line someone after the factory used the wrong part and now the aircraft has a deviation from what should be there and what is there. Sometimes this is minor, other times modifications are not so minor.

Don't fall into the trap of "oh they must have built this plane different" or "they didn't know what they were doing and I must modify something for it to work correctly".

If you can't go by the book, figure out why. Most likely if you can't your plane has been modified. Not necessarily in a good way. You may want to unmodify it.

Bruce “nailed it”. Lots of these old airplanes have been “farmerized” …modified in the “field” without any documentation …sometimes in error…sometimes deliberately by persons unknown or uncaring.

Vertical…I forgot which model 170 you have…but if it’s a ragwing…it’s possible it has an “early” C140 tank….
(The original Cessna PNs were Curtis valves…not SAF Air…but SAF-Air valves may be substituted. The ‘48 models used 1/4’NPT threads…the ‘49 and later used 7/16-20 threads.)

MODEL CAV-160 1/4" NPT For Piper models J-3, J-4, PA-11, -12, -14, -25, -16, -17, -18, -20, -22, -23, -15 and -28 Tri-Pacer; Apache; Champion; Aeronca; Cessna T-50 and earlier 120 and 140 models; and Beechcraft AT-11 and C-18S.


MODEL CAV-170 For all Cessna late 140A models, 150, 170, 170A, 170B, 172 and 175.
Thread size: 7/16-20 NF-3