Fuel Cap Flange not long enough??

[IowaRV9Dreamer]

I am wondering if my fuel cap flanges are OK. These are brand new standard caps from my wing kit. The picture shows the cap in the flange, laying face down on the bench.



What concerns me is that at least 50% of the brown O-ring is unsupported. You can tell by the (blurry) picture - see how much of the O-ring you can see sticking out above the flange. The O-ring is just barely catching the bottom edge of the flange (top edge in the picture because it is upside down).

The flange appears to me to be not long enough. If this was installed, it doesn't seem like it would make much of a seal. If the flange was longer, the O-ring would be more compressed and make a better seal, right? I could imagine with the right tolerance stackup and putting the cap in extra hard that the O-ring might slip off. Why didn't they make the flange an extra 1/8 inch deep?

It looks to me like a defect, but maybe I don't understand the caps or how they seal. It looks like turning the nut might help but these are pretty darn tight already.


Am I completely wrong about this? I'd love to hear from you experts out there.

Thanks!

[Rick6a]

Originally Posted by IowaRV9Dreamer

I am wondering if my fuel cap flanges are OK. These are brand new standard caps from my wing kit. It looks to me like a defect, but maybe I don't understand the caps or how they seal.

Dave,
Your cap is slightly different than the fuel caps on the 6 and 8 but I would think it operates exactly the same way. If so, adjusting the cap is simple, but you have to understand the principle and know what to do. For purposes of illustration, I have included the part numbers on the caps I am familiar with. DO NOT tighten the nut, you will risk breaking the pin on the "latch and post assembly (part 33-ss)....ask me how I know. You need to grab and turn the lower washer casting (called part 83A) clockwise into the top cap casting (called part 63.) Doing this will compress the O-ring and cause it to squeeze out. After adjusting for correct tightness, then turn the jam nut (part 90) down into the washer casting. Refer to the instructions included with and provided by Usher Enterprises with your fuel caps for more detailed information.

[IowaRV9Dreamer]

Thanks Rick - I'll try that tonight. What bothers me is that my O-rings are already pretty tight, and they are still hanging out under the flanges. I think when I tighten them up (which will also move them up, a little) I won't be able to close the caps.

Is this normal to have so much of the O-ring hanging out below the flange?

[kentb]

I also learned the hard way about how to adjust the fuel cap.

I pulled the plane out of the hangar and did my pre-flight. Noticed the right wing cap was not very tight and then proceeded to make it tighter (broke).
The weather was perfect for flying, but it was the week-end I didn't have a spare cap. Monday morning I stopped at Van's (I know some of you are jealous that I drive by my airplane parts store every day) and bought two caps. One to replace the broken one and a spare so that I won't be grounded again. I also bought spare camlock for the oil door, because having lost one of those before at a bad time and I couldn't go flying.

Anyone else have ready spares they suggest having on hand?

Kent

[Rick6a]

Originally Posted by kentb

I also learned the hard way about how to adjust the fuel cap.....Noticed the right wing cap was not very tight and then proceeded to make it tighter (broke).....Kent

Kent, I found out the hard way when I was hot to have the caps anodized red and the anodizer told me to first dissassemble the caps and send only those 2 parts that were to be anodized. The upshot to my story is that because the aluminum is a casting, the anodize process did not work very well and they came out a "dirty burgundy" color as described by the shop so they stripped it all off and sent the caps back no charge. I now keep a spare cap in the airplane. Live and learn.