David Paule
Well Known Member
There are two leak paths - the large perimeter o-ring and the stem. There's a smaller leak path, too, through the lock, but I haven't had to mess with that one yet.
The leak path past the large o-ring is easily cured simply by tightening down the center nut in the bottom of the cap. Be sensitive and try it often, since the sweet spot, where the latch works nicely but the leak is stopped, isn't very large. It's a fraction of a turn to go from too loose to too tight.
I didn't use any lubricant on this large o-ring.
Here's how I dealt with a small but definite leak at the stem.
I used EZ Turn Fuel Lube. There might be a generic version of this fuel-resistant grease available - look for this specification: Mil-G-6032D. It's a very sticky, thick paste and you certainly won't need much.
Here's a photo of a disassembled cap. The arrow points to the stem. Just to the right of the arrow is the o-ring. I added the grease in this area, paying particular attention to the o-ring.
Mostly hidden by the upside down cap casting is a washer on top of the bore, you can barely see it through the bore. This washer is the bearing surface for the heels of the cam part of the lever. It's also the outer race of the o-ring bore in the casting, so I added some of the grease on that area too, before reinstalling the washer.
The order of reassembly was to install this washer on the stem, insert the stem in the bore, slip the coil spring over it, then the black plastic retainer, and finally the small washer and the nut.
My RV-3B has a long way to go before I get any fuel in the tanks, so be aware that this was tested with air pressure, under 1 psi, not fuel in flight.
Dave
The leak path past the large o-ring is easily cured simply by tightening down the center nut in the bottom of the cap. Be sensitive and try it often, since the sweet spot, where the latch works nicely but the leak is stopped, isn't very large. It's a fraction of a turn to go from too loose to too tight.
I didn't use any lubricant on this large o-ring.
Here's how I dealt with a small but definite leak at the stem.
I used EZ Turn Fuel Lube. There might be a generic version of this fuel-resistant grease available - look for this specification: Mil-G-6032D. It's a very sticky, thick paste and you certainly won't need much.
Here's a photo of a disassembled cap. The arrow points to the stem. Just to the right of the arrow is the o-ring. I added the grease in this area, paying particular attention to the o-ring.
Mostly hidden by the upside down cap casting is a washer on top of the bore, you can barely see it through the bore. This washer is the bearing surface for the heels of the cam part of the lever. It's also the outer race of the o-ring bore in the casting, so I added some of the grease on that area too, before reinstalling the washer.
The order of reassembly was to install this washer on the stem, insert the stem in the bore, slip the coil spring over it, then the black plastic retainer, and finally the small washer and the nut.
My RV-3B has a long way to go before I get any fuel in the tanks, so be aware that this was tested with air pressure, under 1 psi, not fuel in flight.
Dave
Last edited:
