Leaky Fuel Selector Valve - O-Ring Issues

[Bill Tew]

After only a few hours of flight time, I needed to make some adjustments to my Carbon Cub EX2 and drained the fuel from both tanks and cleared the fuel lines. Life's obligations got in the way and the aircraft sat for ~ 4 months with no fuel. When I next added fuel back - 5 gal in each tank - the fuel selector valve leaked profusely in all positions. Removing the selector barrel (while being careful to capture the 2 small springs with ball bearings at either end of each spring), and replacing the 2 O-rings around the selector barrel stopped the leaking. (O-ring P/N MS29513-114 available from Aircraft Spruce, Wicks, and others).

Upon the first flight following the fuel selector valve issue, observed that #4 cylinder was running very cool and the engine ran rough at low to mid rpm ranges. Checked to assure that the primer was closed and locked but the problem persisted. Disconnected the primer line from #4 cylinder and gascolator (plugged holes in both) and ...... yep.... the rough running disappeared and the EGT of #4 cylinder was back in line with the others. It would seem that these O-rings failed like those in the fuel selector valve and the suction from #4 cylinder was enough to pull fuel through the primer even with the primer closed and locked. Replacement O-rings (P/N 05-11936) for the ACS 10920 fuel primer are available from Aircraft Spruce and The Pilotshop.

I don't know what caused these O-rings to start leaking after working perfectly before the fuel was drained. My home field, KHCR (Heber City, UT), is at 5,620' and very dry - high humidity in the summer is only about 30% adn usually much less. Perhaps those conditions adversely affected the 0-rings. Needless to say, I ordered extra O-rings.

N5491D is back flying now between the ever persistent snow storms here in the Wasatch mountains.

[Pete D]

It is common for o-rings in the fuel selector to dry out if they have been put into service then the fuel drained for an extended period of time. Selectors that have never had fuel in them do not typically have that issue, it is just when they have been in service then the fuel is drained and they dry out.

I have not run across the same thing with the primer, but that makes sense and is good info. Which primer do you have? the older version that is anodized with a slight yellow/green tint to it or the newer bare aluminum one?

[Dan L]

Interesting Pete that o-rings that have seen fuel would be more prone to leak when fuel is reintroduced later. I wonder if a bit of EZ Turn would prevent that?

I have that same primer. I’ll keep this in mind. That was a good diagnosis.

I replaced o-rings in the valve last condition inspection. The worst part is draining the tanks.

[Bill Tew]

I have not run across the same thing with the primer, but that makes sense and is good info. Which primer do you have? the older version that is anodized with a slight yellow/green tint to it or the newer bare aluminum one?[/QUOTE]

My fuel primer is bare aluminum. I believe its an ACS model 10920

Bill

[Mark Keneston]

After only a few hours of flight time, I needed to make some adjustments to my Carbon Cub EX2 and drained the fuel from both tanks and cleared the fuel lines. Life's obligations got in the way and the aircraft sat for ~ 4 months with no fuel. When I next added fuel back - 5 gal in each tank - the fuel selector valve leaked profusely in all positions. Removing the selector barrel (while being careful to capture the 2 small springs with ball bearings at either end of each spring), and replacing the 2 O-rings around the selector barrel stopped the leaking. (O-ring P/N MS29513-114 available from Aircraft Spruce, Wicks, and others).

Upon the first flight following the fuel selector valve issue, observed that #4 cylinder was running very cool and the engine ran rough at low to mid rpm ranges. Checked to assure that the primer was closed and locked but the problem persisted. Disconnected the primer line from #4 cylinder and gascolator (plugged holes in both) and ...... yep.... the rough running disappeared and the EGT of #4 cylinder was back in line with the others. It would seem that these O-rings failed like those in the fuel selector valve and the suction from #4 cylinder was enough to pull fuel through the primer even with the primer closed and locked. Replacement O-rings (P/N 05-11936) for the ACS 10920 fuel primer are available from Aircraft Spruce and The Pilotshop.

I don't know what caused these O-rings to start leaking after working perfectly before the fuel was drained. My home field, KHCR (Heber City, UT), is at 5,620' and very dry - high humidity in the summer is only about 30% adn usually much less. Perhaps those conditions adversely affected the 0-rings. Needless to say, I ordered extra O-rings.

N5491D is back flying now between the ever persistent snow storms here in the Wasatch mountains.

i am in upstate NY and humidity can be high in Summer. Store age of the plane in any season is with full fuel to prevent moisture and keep seals, o rings etc soft. Hope it helps