Fuel Valve Rebuild
Hello all. My fuel valve started leaking when I selected the left tank. I couldn't see any fuel stains so when I took the fairing off the floor and turned to the left tank, I could see fuel slowly leaking down the face of the valve. Time for a rebuild. Upon looking at the ISC Knowledge Disc, I didn't see any instructions on how to take the valve apart. They all said, disassemble valve. So, in an effort to help others out, I will describe what my valve looked like as I took it apart. It has been a couple of days since I did this so if I describe this incorrectly, let me know so I can fix it. Please drain all of the fuel out of your aircraft before attempting this so that you don't have fuel all over the inside of the airplane.
First, you need to pull the selector lever shaft off the valve. To do this, you need to remove the fairing that is between the two sets of rudder pedals. Then you follow the selector valve shaft to the valve body on the cockpit side of the firewall. Once there, you will see a cotter pin. Remove the cotter pin and then pull on the shaft handle and pull it away from the instrument panel. There should be three flat sides and one rounded side on the valve shaft so that the selector shaft handle only goes on one way.
Once that is complete and out of the way, go down to the valve body. The valve cap has two flats on it that are set up for a large wrench. Put a wrench on that and also a wrench on the bottom of the valve body that contains the line that goes to the engine. You want this second wrench as the cap will take some force to come off and you don't want the entire valve body to rotate away from the firewall and fuel lines. The second wrench on the bottom line will stabilize the valve body and prevent it from rotating. It may take a decent amount of force to get the valve body cap to loosen.
Once loose, you can rotate it off by hand. There is a spring inside the valve that will assist in getting the cap off but it doesn't have the force to make parts go flying. When it comes off, I had a thin metal washer between the cap and the valve body. Make sure you set both items aside. On my airplane, there was an O Ring on the inside of the Valve Body cap where the shaft comes through and that was worn which was causing the leak.
After that you will see a small brass cap that is sitting on the spring in the valve. Remove both of those items and pay attention to the order they are in as they will need to go back in the same way that they came out. Set them aside.
After that there was another brass cap or washer which was sitting upon a circular metal flat that a half circle little tab on one side and four slots cut in it slightly smaller that two metal shafts that are perpendicular to the valve. These shafts sit in the slots in the metal flat and are the detents for the fuel valve. Carefully remove these items. The circular metal flat may not come out without removing the valve core as the half circle tab fits into a small cut out in the threaded area where the overall valve cap screws. This is to hold the tab in place so that the detent washer doesn't move and you can feel the detents when you turn the fuel tank selector switch.
Finally, remove the valve core from the valve. Pay attention to the way this is oriented. The fuel line from the left tank comes from the left side of the airplane past the valve body to the right of it and then loops back 180 degrees to the valve body. If you don't catch this, you may put the fuel valve in 180 degrees backwards. The right side fuel line does the opposite. If comes in from the right side, goes past the valve body, and does a 180 degree turn to enter the fuel valve from the left side of the valve body.
Reassebmly is in the opposite order:
Detent Washer (watch where the cutout is to put the half circle tab from the detent washer into that cutout so that it doesn't rotate and you can feel the detents when reasembled)
Brass spring cap
Brass washer on the Valve Cap
Fuel tank selector shaft.
Considering that I have very little mechanical experience (and with the assistance of my local A&P IA) and I was able to easily figure this out means that it isn't beyond your capabilities either. A couple of notes. My Valve core and valve body were in good shape so that I didn't need to be polished. Check yours out. If it has a lot of scoring, you may need to get valve polishing compound or something similar and clean up your valve before you reassemble it.
Also, the type of material used to seal the valve around the selector shaft may not be an O Ring like mine was. I have heard of leather seals and another type of seal. I would replace your seal material with whatever that you took out of the valve. I also found that my detents were much easier to feel once I had rebuilt the fuel valve.
Finally, when I got it all back together I did some test engine runs. My engine would run fine on the right fuel line but it did not like running on the left fuel line for more than roughly 10 seconds. It took three or four starts before it started running normally. I got more fuel, did an engine run up, a Static RPM check, and a high speed taxi and abort before I took the airplane into the air for a test flight. Even then I stayed right over the airfield just in case. These were my precautions and hiccups. I am not saying you will experience any of these but I pass them along in case they may be of value for your situation.
Karl A Vogelheim
Great post! Was yours a 1/2" or 3/8"?
Since you have rebuilt the Imperial Eastman valves both 3/8” and 1/2” maybe you would know this.
I’m rebuilding the 3/8” valve that was already removed from my project. Do you have a part number or source for this flat copper gasket? Mine is damaged and I would like to replace it but I have no references materials to the valve. I guess I could file it down but if you know of a replacement that is the way I would like to go.
I don't have a source. One just has to get creative and look at other applications that use similar flat cooper washers as gaskets. Plumbing parts come to mind, but there are lots of automotive things that might be found that have similar copper washers. ID would be what you are looking for and thickness. OD I don't think would have to be exact.
Larry Wheelock, A&P/IAStinson 108 N584LW 180 LycTexas in Winter; Indiana in Summer
Thanks Charles....Below are the mic’d dimensions for ID and OD, I need to get back down there and measure the thickness.
It appears what I thought was “Damage” to the OD of the washer, was really used as a bendable tab to help secure the Nut on the hosing.
Will, I have received the brass stock I ordered and if you'll give me the thickness of the washer, I'll see if I can make you one. Cheers
Stinson 108-2 NC9502K
Sorry this took so long, three times I was at the hangar and forgot but my 56 YO brain kicked in today and I remembered!
Looks like 0.046
You know I missed something while discussing making a new washer. The original was out of copper and I made the new one out of brass. I wonder if the brass will seal as good as the copper one did? I'm anxious to know how it worked out.
Stinson 108-2 NC9502K
Being that its not a “Crush” washer, I think its going to do just fine especially since a replacement is not available. The Flat nature of this work well. I have dressed surfaces so I will report back later. Not sure when I will “Leak Test” as I’m still running fuel lines. Thanks Charles
Larry, let me ask you a question on another subject. My son is starting the annual on our aircraft and noticed something he was concerned about. The strut fairing screws are actually screwed into the strut. I can't remember. Is this proper?
Stinson 108-2 NC9502K