Fuel selector valve

[Skymaster337B]

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

[wslade2]

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]

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

Thanks,
Jeff

[wslade2]

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]

Thanks - totally understand about the microprojects.

Jeff

[wslade2]

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]

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.