Fuel selector valve

wslade2 · #1 11-25-21, 05:37 AM

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 · #2 11-25-21, 05:38 AM

more fuel valve repair pictures attached

wslade2 · #3 11-25-21, 05:45 AM

last set of pictures

edasmus · #4 11-25-21, 10:52 AM

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

TomM · #5 11-27-21, 10:07 AM

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 · #6 11-28-21, 01:47 AM

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

wslade2 · #7 11-29-21, 12:20 AM

Service bulletin says to remove the ball from the port that is not connected so the valve can “operate in all temperatures.” My guess, some water gets behind the ball in that closed off cavity, freezes, jams the ball so it can’t be pushed back and that probably jams the cam and valve.

Thanks for noting that.

JAG · #8 01-06-22, 04:44 PM

just following up on this thread - did you happen to have P/N's for the o-rings you could share?

Thanks,
Jeff

wslade2 · #9 01-06-22, 10:52 PM

Going to have to admit to a degree of disorganization here. Had a lot of 337 microprojects since then with stuff scattered around including o-rings, lots of o-rings.

But...I had bought a viton o ring assortment from Harbor Freight for various uses on my 337 project. For the shaft there was a perfect fit out of that assortment but can't recall which compartment with the exact measurements. I wrote down the measurements of the original shaft o-ring as 0.5" OD x 0.4" ID x 0.05" CS (cross section). Realize that's the compressed old o-ring measurements. Nothing out of that assortment, though, fit the ports with the balls. I'm pretty sure those were 5/16" ID x 7/16" OD x 1/16" CS (cross section) that I purchased online from the o-ring store. Again, all in viton as the parts manual specifies. Sorry for being a little scattered on that now.

I lubricated the shaft/o-ring with EZ Turn fuel lubricant (grease) available from Aircraft Spruce. My mechanic turned me on to this while dealing with some fuel fitting issues and it is designed to be used in high octane fuel environment.

Speaking of the o-ring store, they've been a life saver for o-rings. A fellow pilot with a piper Lance had a leaking fuel drain/valve unit due to the tiniest worn o-ring. No body had this o-ring, not even piper could help him, except buy used $3000 hardware off ebay (no-one wants to rebuild the unit). They were able to confer with mechanic and send an assortment of o-rings around the shaft size with finally one that ended up working.

JAG · #10 01-07-22, 12:25 PM

Thanks - totally understand about the microprojects.

Jeff

wslade2 · #11 07-10-22, 08:40 PM

Just an update now about a year after my fuel valve rebuild. Only residual issue is that I cut the gasket for the valve from nitrile hoping to update the situation. (recall no one makes the gaskets for these valves anymore and one will have to be made from tracing the old one and raw materials).

I over tightened the nitrile making it squish out the sides some. This lead to the exposed part of the nitrile cracking. I am concerned that the cracking may migrate to the interior and lead to some leaking. So I am going to cut/replace the gaskets with new self made gaskets of gas proof carburetor material from the local auto store (a rubberized paper material; I think the original were cork).

I ran into this when installing CiEs probes I'm doing now. Their supplied nitrile gaskets at the tank adapter plate squished too much with the torque recommendations for screws. So mechanic and I eyeballed that and went lighter on the torque. Could still try to use nitrile but not be as aggressive with the screw down. But since valve near low point of system, going to go with the other material and make the screws "tight-tight".

also courtesy another member mention (Mr. Skymaster 337B) the following: https://support.cessna.com/custsupt/...df?as_id=52067 (ME 81-19)
Not an expert but I don't think the models with simplified tank setup like G model have the unused port...

wslade2 · #12 10-02-22, 01:15 PM

while working on CiES probes I replaced o-rings at the close off balls in my other valve. They were definitely on their way out once removed and inspected. (on the other valve one had totally disintegrated and disappeared.)

O-ring size confirmed: 5/16 " ID x 7/16" OD x 1/16" cross section (CS)
Again, this is where the ball will press against the valve cavity port/o-ring to provide positive shut off. I used fuel resistant o-rings.

If you use a right angle pick and firmly pull, you can pull out the main retaining ring without damage for reuse. Might have to grind pick end short to fit. I pull it out while holding it down in a 5 gallon bucket so that when it "pops" the spring and ball don't go flying. It'll be a pretty strong tug. There will be another smaller retaining ring holding the o-ring in place. Retaining rings can be pushed in with screw driver and positioned. For the main ring, which can be stubborn, once past the first few threads can use an AN fitting to "press" it all the way down.

Used fuel resistant gasket material from auto part store to make valve body gaskets by tracing valve and old gasket. $9 leather punch from harbor freight to punch out screw holes. The material I got was thin so had to double it to get right thickness. First inspected valve operation visually after reassembly and then tested valve by blowing air through it before putting it back in.