Fuel selector valve

[wslade2]

I have 1970 337E with the original, not simplified, fuel system with main and switch to aux tanks setup. Not the simplified later (G model and above I believe) fuel tank set up.

As part of my plan when I purchased aircraft I knew I would want fuel selector valve overhaul at some point. However that was forced upon me this season when my fuel selector valves locked and would not move into crossfeed position. If they wouldn't move into crossfeed, the concern was soon the wouldn't move between main and aux as well. I disconnected the cables and confirmed the problem was not the linkage but the valves themselves.

I had already done some search in the months before looking for overhaul options and could find no establishment that would overhaul the valves, which was why I stopped worrying about it. Briefly, McFarlane was hopeful when I called and they said they were "keeping a list" of requests for capabilities and my name was "added" to the list of 337 requests. But still nothing. Called multiple overhaul facilities. Other members here posted similarly no luck finding a facility.

I made many calls and searches to no avail regarding the issue of the fuel valve gasket trying to chase down anyone one with one or the original manufacture. Did find some interesting history of original manufacturer getting absorbed, called them, no help. No one making them.

So, looked like me and my shop were going to become the way to overhaul my valves. I had already purchased a terrible example of a valve off e-bay some months before to use for an autopsy. When it came, it looked like it had been under water for years and was frozen solid, non-functioning. If I could get that working, I figured I could do mine.

So, I am going to try and post pictures of what I did. My valves had locked up due to rust build up in the "cup" and this was making the "cam" (a cross shaped actuator that pushes the balls open to allow fuel to flow out of a portal into the main chamber, "cup") bind. I had also had a problem with one of my portals not providing positive cut-off and that was ultimately found to be deteriorated o-ring.

The inability to find a sealing gasket problem was resolved by simply tracing my original gasket on to some gasket material and cutting a duplicate and punching holes in it for the screws.

With care, the retaining rings for the springs and balls can be removed and reused and used a L-shaped pick to get the rings out. They can be "pressed" back in buy starting them by hand and using AN fitting to screw/press them all the way back down. Behind the balls, are the sealing o-rings. I measured and replaced. Be sure to use fuel resistant o-rings. The shaft of the selector also uses a fuel resistant o-ring. I cleaned this up and replaced o-ring, lubricated the shaft with aircraft grade fuel lube/grease (available aircraft spruce, etc). Reassembly was a snap. Punches were used to get the roll pins out and because autopsy valve was frozen, had to use a punch to get the selector with the cam out of the housing.

Hopefully pictures are self explanatory and this helps someone.

I ended up replacing cable linkage while I was at it and everything works better than before.

There is a limit on pictures so I will attach more pictures to a continuation of this post

[wslade2]

more fuel valve repair pictures attached

[wslade2]

last set of pictures

[edasmus]

Excellent work and fine post! Thank you for sharing. Amazing...

[TomM]

Awesome!!

Do you have the o-ring part numbers you can share? I would like to do mine as when the valve is off, the fuel from the port side main tank drains back into the reserve tank and then out the overflow. If both tanks are full, it will leak over 10 gallons in a week before the pressure is low enough to stop the flow. So I now I park it with full main tanks and empty reserve. I prefer to keep them all full.

Thanks!!

[Skymaster337B]

Before you overhaul the fuel valve check out Cessna Bulletin ME81-19.