[f-AA] fuel valves

[tom boyle]

I have a leaking ¼ turn conical fuel valve that has started seeping.

Can it be lapped with compound or is there some other solution?


Tom

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[Richard Holcombe]

EZ Turn

It is a grease that is non soluble in avgas. Don't use too much and get a glob of it town the line.

Could be just an O ring or packing around the stem of the valve.

[Jeff Kimball]

Tom:

I just went through this with my L16. The biggest question is where is it leaking? Inlet to outlet (fuel won't completely shut off) or out of the valve body around the valve stem?

Mine exhibited a bit of both...

First read this:

http://johnpropst.yolasite.com/resources/fuel%20shutoff%20valves%20overhaul%20rev7.pdf

Good stuff...

As for the leak, inlet to outlet, fuel not shutting off, what I discovered was the little pin that goes through the valve stem that interfaces with the "C" washer was worn and the valve was actually turning past "Off" and coming back "On". A new pin will fix that. (see the photos in John Probst article.)

If the valve internal cone is worn or rusty, a bit of lapping could help. Be careful as too much will destroy the valve.

As for the leak around the valve stem, mine is an early valve like shown in the Probst article which uses a spring loaded double cone seal as shown on the last page of the article. John Probst labels it as a graphite seal. Mine was stuck in the portion of the valve that unscrews (the valve bonnet), held in place by some sort of very fine mud.. The mud is probably from decades and decades of fuel sediment. With a little TLC, some spray carburetor cleaner and an overnight soak in penetrating oil, the seal was convinced to come out of the bonnet without damage. From all appearances the seal was fine and still flexible, it just couldn't move due to the mud packed around it so the spring pressure wasn't compensating for any wear.

Apparently the later valves use "O" rings which are easy to replace.

With it all cleaned up and a bit of the fuel lube (careful with this stuff, too much can cause problems) the valve seems to work fine and not leak.

Good luck

Jeff, L16a and a K.

[tom boyle]

Jeff, it's leaking out the valve stem.  It is worse with the valve
closed than if I leave the valve open between flights. Thanks for the
reference.

Tom

['Botijo G' via aeronca]

O ring. Be sure to get the right MS that is fuel proof

[Jeff Kimball]

Early valves don't/can't use "O-rings". they have the double cone seal as shown in Probst drawing. Be sure which valve you have. Putting O-rings in an early valve is a sure way to have a problem.

Jeff

['Botijo G' via aeronca]

Yeah if it doesn’t have one don’t try to put one it will make it much worse

[tom boyle]

Good info!  I'm going to drain the tank, dismember the valve and try to
reverse engineer it to see if an o-ring would make a difference.  It has
an annular wavy spring to provide sealing tension that is supposed to
provide the pressure to seal the valve  Just didn't know if an o-ring
was needed too.

Will report results.

[Sal Capra]

I have the earlier valve.
This last annual I was on a mission to cure all the blue seeps.
I replaced the gascolator, large copper fuel line and rebuilt the valve using 2 o-rings and a dab of fuel lube. I tried to press graphite packing in as Bill Pancake outlines with no joy. ..... been over 2 months. Valve got a little stiffer. I got the o/rings in the Ace hardware Aviation dept.


Sal Capra
Sent from my iPhone

> On Jan 2, 2021, at 11:18 AM, tom boyle <tomb...@charter.net> wrote:
>
> Good info! I'm going to drain the tank, dismember the valve and try to reverse engineer it to see if an o-ring would make a difference. It has an annular wavy spring to provide sealing tension that is supposed to provide the pressure to seal the valve Just didn't know if an o-ring was needed too.

[James Beckman]

My 1941 chief gas valves did not use any shaft seals. They are a tapered cone type valve that depended on a lapped cone and the gas-proof grease for a seal. 2 problems can occur with this type valve. 1  as the cone and bore wear over time, the cone moves inward but will still seal. However the stop pin used to limit rotation to 90 degrees will bottom out and will keep the cone from seating. Was cured by making the grove the pin sits in deeper with a small file.

Now, problem #2. My valves only had a 1/4 inch bore for gas flow. As the cone and body wear, the cone moves inward and the holes between the cone and valve body no longer line up reducing the diameter of the bore to less than 1/4 inch. This COULD cause restricted fuel flow at full power. To much sticky grease can cause same problem because gas will not wash the excess grease out of the hole. Low fuel, full power and nose high can get your attention right now. Be careful, have fun and happy new year.

Sent from my U.S.Cellular© Smartphone

[tom boyle]

My valve is, I think, the cone variety.  I am going to look at that bottoming out possibility.

Thanks,

Tom

[Jeff Kimball]

On my cone seal, the seal was "stuck" in the bonnet which means the spring couldn't compress it to compensate for wear.  Once I got the seal out of the bonnet and everything all cleaned up it seemed fine.  The dimensions of the seal were almost identical to the drawing in the Probst article and it still seemed a bit pliable so the spring pressure can force it against the cones and make it seal.

 

FYI

 

Jeff