170A Fuel Selector Valve Leak

[dstates]

Well, the never ending annual inspection reared it’s ugly head again. I walked into the hangar to find a puddle on the floor and a belly that looked like this:

After some investigation we could see the occasional drip coming from the fuel selector valve and the leak was at the top of the valve. I spent the rest of that evening draining fuel tanks. Note: this is the brass valve, not the machined aluminum block version that is on the 170B.

Next came the research. Another huge thanks goes out to the members of this association as I was able to find a lot of info on this issue here as well as the 120/140 association forum. At this point I have the valve out and the new o-rings were just delivered this afternoon. I hope to have it back in the plane this weekend. Internals look good, just needs a new seal and some fuel lube. And I’ll definitely be making a plate with two nut plates for ease of assembly.

My one question is... there is a washer that goes above the spring and it has a concave side and flat side (I didn’t take note of the orientation during disassembly). Since I’m replacing the packing with an o-ring should the concave side go against the spring?

Here are some pictures of the work so far. I’m also attaching a file I made with a bunch of reference info from various sources. It seems that different versions of this valve were also used by Piper and the Cessna 20/140 so there is some info from those valves as well.

[dstates]

Here is a copy of my current reference info file. Again note, this is for the 170A valve, not the 170B.

I hope to post an update after this weekend with it fixed.

170A_fuel_selector_valve_info.pdf

(780.47 KiB) Downloaded 372 times

[Bruce Fenstermacher]

I believe the cup would go up against the packing or o-ring in your case. This would force the packing or o-ring into the stem. Going the other way would force the packing or o-ring away from the stem.

Besides the illustration in the IPC looks like the cup is up.

[dstates]

I put the valve back together today. The packing was much thicker than an o-ring so I ended up using multiple o-rings in order to compress the spring some so I could feel the detent. I considered adding a couple washers, but their OD was too big. I haven’t installed the valve back in the plane yet. Any concerns with using multiple o-rings?

By the way, a couple street elbows makes the drain line up with the hole in the belly. I can’t take credit, I got this idea from another post on this forum. Aircraft Spruce part # 3400X2.

[Bruce Fenstermacher]

I noticed the street elbows. Great ideal.

As for the multiple o-rings. I can't think of a reason not to use multiple if need be. Anyone else have an opinion?

[GAHorn]

I’m relying upon memory from several years ago when I rebuilt one of these...

I seem to recall the “packing” was nothing more than two o-rings. My question is: Why is your packing “much thicker than an O-ring” when two O-rings ARE the packing?

They WILL be slightly thicker because they’re new.... IF you’ve used the correct replacement sizes. Where and How did you obtain the replacement parts? What is/was your source?

The “detent” of this valve was never especially noteworthy. The only ones I’ve operated were barely noticeable.

===================

On an entirely different wavelength: I recently purchased the modern version of this same valve for the purposes of adding an auxiliary fuel tank to my pontoon boat and I’m impressed with it’s quality and operation. If I had an airplane with this valve that was not rebuildable.... I’d replace it with the modern WeatherHead/Moeller valve and get on down the airway. The only differences I can detect is the new valve uses modern materials such as a synthetic cone instead of sold brass cone, and the fact that the cone is not capable of BOTH position for the wing tanks without drilling an additional hole... which I believe should be an easy matter. The shaft (in pictures) appears it might need to be shortened and carefully fitted for length but in reality that appearance is misleading due to the difference in the “bonnet”/top-nut height, but even if so, a hacksaw and file should make that simple. (The modern valve uses a phenolic/synthetic cone and does not require a heavy/long spring to force the cone into the body, therefore the top-nut does not need to contain a spring assembly of the same length. The modern valve is physically the virtual replacement part with the previously mentioned exception for “Both” fuel tank selection which, again, might be a simple mod to the cone. The valve likely doesn’t even need disassembly to modify the cone.... a drill, carefully inserted thru the side-port would work I believe. It’d cost $28 to find out.)

https://www.amazon.com/Moeller-Three-Wa ... B000MTI18M

[dstates]

I’m relying upon memory from several years ago when I rebuilt one of these...

I seem to recall the “packing” was nothing more than two o-rings. My question is: Why is your packing “much thicker than an O-ring” when two O-rings ARE the packing?

They WILL be slightly thicker because they’re new.... IF you’ve used the correct replacement sizes. Where and How did you obtain the replacement parts? What is/was your source?

The “detent” of this valve was never especially noteworthy. The only ones I’ve operated were barely noticeable.

George,

I did not have an o-ring in my valve when I took it apart. My plane sat in storage for over 30 years in its past and I’m guessing this was original packing. It was a felt like packing like what I’ve used on my 1952 Farmall tractor. The parts catalog shows a quantity of two for the packing and in my valve I pulled out two “pieces” one came out still disk like and the other tore when I took it out. Overall thickness of the two pieces was probably 1/4” or so. I had considered the new Weatherhead valve, but my A&P wants that to be a last resort. I appreciate the good review on it, though.

I got the o-ring number from this forum (MS29513-011) and ordered a half dozen from Spruce.

I hope to get the valve installed today and leak test it. I guess that will tell the story.

[hetch]

This must be the season to take those old valves apart and try to get them to rotate again. So I have mine apart and in my hand.

dstates » Thu May 07, 2020 7:04 pm

My one question is... there is a washer that goes above the spring and it has a concave side and flat side (I didn’t take note of the orientation during disassembly). Since I’m replacing the packing with an o-ring should the concave side go against the spring?

I believe that you have the cup in the wrong place. Although I have owned our plane for 31 years, IIRC from the logs only a few years before we bought it the fuel valve had been replaced with a new one. I did try to keep careful track of the orientation of the parts the few times my mechanic and I have needed to service it, so I think what I'm telling you is correct. I have the same parts, but they are assembled in this order from bottom to top:
- cone w/pin & stem
- keyed detent washer with slots
- cupped washer facing down (you will notice the cup opening is larger than the top of the cone above the pin, so the spring force is pushing the cone washer against the slotted detent washer down against the pin which gives it the detent action, and also the spring will then sit higher on the shaft
- spring
- flat washer
-packing

Look at your slotted detent washer. I expect that you will see minor wear from the cup OD pressing (possibly rotating) on the top of the slotted detent washer. Of course if you have flipped the detent washer to get sharper detents (they were never that great, but they are better if you go to the unused side, and the washer is symmetrical so the detents end up in the same place) you will need to look at what was the top. If you see that circular wear, it was from the cup, since the spring is smaller diameter and would bottom out on the top of the plug it would not cause any wear on the detent washer.

Assembled as you have shown, I believe you will have no detent action, and too much space at the top of the spring, thus requiring you to stack several o-rings. The packing or o-ring(s) has space for it in the machined area in the cap.

Let me know if this makes sense to you after you try stacking them up in the order I suggest.

[dstates]

This must be the season to take those old valves apart and try to get them to rotate again. So I have mine apart and in my hand.

dstates » Thu May 07, 2020 7:04 pm

My one question is... there is a washer that goes above the spring and it has a concave side and flat side (I didn’t take note of the orientation during disassembly). Since I’m replacing the packing with an o-ring should the concave side go against the spring?

I believe that you have the cup in the wrong place. Although I have owned our plane for 31 years, IIRC from the logs only a few years before we bought it the fuel valve had been replaced with a new one. I did try to keep careful track of the orientation of the parts the few times my mechanic and I have needed to service it, so I think what I'm telling you is correct. I have the same parts, but they are assembled in this order from bottom to top:
- cone w/pin & stem
- keyed detent washer with slots
- cupped washer facing down (you will notice the cup opening is larger than the top of the cone above the pin, so the spring force is pushing the cone washer against the slotted detent washer down against the pin which gives it the detent action, and also the spring will then sit higher on the shaft
- spring
- flat washer
-packing

Look at your slotted detent washer. I expect that you will see minor wear from the cup OD pressing (possibly rotating) on the top of the slotted detent washer. Of course if you have flipped the detent washer to get sharper detents (they were never that great, but they are better if you go to the unused side, and the washer is symmetrical so the detents end up in the same place) you will need to look at what was the top. If you see that circular wear, it was from the cup, since the spring is smaller diameter and would bottom out on the top of the plug it would not cause any wear on the detent washer.

Assembled as you have shown, I believe you will have no detent action, and too much space at the top of the spring, thus requiring you to stack several o-rings. The packing or o-ring(s) has space for it in the machined area in the cap.

Let me know if this makes sense to you after you try stacking them up in the order I suggest.

Glenn,
I appreciate the info. I do have the cupped disk down on top of the detent washer. The piece I was asking about is the washer right below the packing. Mine has a flat side and a curved (concave) side. I ended up putting it concave side up towards the o-ring.

I got the valve installed back in the plane today and it leaked again. I’m going to try a little harder to find some packing instead of trying the o-ring. Did you get new packing or are you using an o-ring?

[dstates]

To those following my issue and any future 170A owners fighting this issue. I have discovered today that there were multiple versions of the Weatherhead brass valves over the years. I believe mine to be original and the cap on the valve had a graphite like packing cord in the top of the cap as the seal for the shaft as shown in the parts catalog). The cap has a taller dome and only two wrench flats. I’ve now seen another valve that came out of a 170A that had a shorter cap that looks to be machined internally for an o-ring. This cap was shorter (didn’t need room for packing) and had a full hex for the wrench.

I don’t believe that the packing from my valve with the taller cap can simply be replaced with an o-ring (or multiple o-rings as I tried). If you are lucky enough to have the shorter cap with the full hex you may be able to just use a new o-ring.

[Bruce Fenstermacher]

Doug, I'd venture by a good plumbing supply house looking for that graphite packing. It was used in old faucets and many other places. I may have even seen it at my local ACE Hardware.

[GAHorn]

That packing was made with hemp-cord-and-graphite or with asbestos-and-graphite and may explain why it is not commonly found today. If you go to ACE hardware today and ask for faucet/valve-stem packing, you will likely be handed a teflon-cord type. Not sure I’d use that with fuel.

Here’s a source for alternatives:
https://www.danco.com/product-category/ ... m-packing/

Here’s what may be closer to original:
https://www.amazon.com/Plumb-Pak-PP810- ... 341&sr=8-6

[dstates]

Thanks for the support everyone.. I've got a couple items on order to see what works best. I'll report back with what I get (probably a few days before everything arrives) and how well it works.

Doug

[dstates]

Here’s my update. I have my fuel selector valve fixed.

I got the fuel selector removed and made a nutplate to replace the two loose nuts on the bottom of the valve. I recommend that for anyone else in the future.

I was able to procure an Anderson Brass Co. valve that is available online in a few places. I got it as a backup plan in case I couldn’t get my original valve to seal. My main hope was that I could take the cap off the Anderson Brass Co. valve which uses an o-ring and replace my cap that uses packing. Unfortunately that didn’t work as the thread was different. It looked like such a great solution, though, that if I fight this battle again I will probably have someone machine a new cap for me that will use an o-ring seal.

So, I ended up using some graphite packing I purchased on Amazon and was able to get the valve to seal. The packing is 1/8th inch square cross section. I used two pieces that were 1.75” long. I wrapped them around a 1/4” punch in the cap of the valve and then used a smaller punch to pack it down into the cap. Then I slid the cap over the valve stem. If you go this route it may take a couple attempts to get the right amount of packing in there. My first attempt I didn’t pack it in and it leaked again. The second time I put in too much and I couldn’t rotate the selector stem because the spring was compressed too much and the detent was keeping it from rotating.

In the end, I have my system with just the right ratchet, wrenches and arm position in one of the floor access panels and I can swap out the valve in less time than it takes to drain fuel out of the tanks.

My A&P IA was a great help as well and is comfortable with how this ended up.

Thanks, everyone, for the info and tips.
Doug

[gfeher]

Doug, your fuel valve may be an Imperial fuel valve. They made a 3-port fuel valve like yours. The later ones used o-rings rather than packing. Although some sell used ones from aircraft on Ebay for ridiculous amounts, occasionally someone sells one for parts (or just the body and cap) for short money. If you are just looking for the cap, you might look there.