Tip: Gas Caps

hevansrv7a · #1 03-12-2008, 01:31 PM

Today I found out more about the standard gas cap than I wanted to know. I'm probably the only one who didn't know, but just in case:

1. The big nylock nut on the bottom is just a lock nut; the thing that adjusts the preload on the big brown O ring is the bottom disk and you have to loosen the locknut first. Then turn it clockwise to tighten.

2. If you try to adjust the O ring preload by turning the nylock nut clockwise you stand a good chance of breaking the roll pin. Guess how I know. Besides, it just locks the two pieces together and does not adjust anything.

3. The roll pin, once broken, can be driven out easily with a 1/16" drill bit shank. In a pinch, the same shank can be used to substitute for the roll pin. I don't recommend this as a permanent fix because I think it reverses the hard-soft design and thus the wrong thing would wear out first. The drill bit shank can be used because the design of the cap captures it even though unlike the roll pin it is not tight in the holes. My replacement parts are on order.

4. There is a replaceable small O ring around the stem under the little square metal plate visible where the flipper rubs. That could leak around the stem.

rvpilot · #2 03-12-2008, 02:48 PM

at your local National Airplane Parts Associates (NAPA).
Ask me how I know!!!

Geico266 · #3 03-12-2008, 06:12 PM

Good points. I don't understand how they are water tight. When ever I stay over night and expect rain I duct tape them shut.

Mel · #4 03-12-2008, 06:45 PM

They ARE water tight when adjusted properly. 15 years, no water!

Geico266 · #5 03-12-2008, 06:47 PM

Quote:

Originally Posted by Mel

They ARE water tight when adjusted properly. 15 years, no water!

The tape also lets me know if someone is stealing fuel!

I've tried several times to get them water tight. I guess I'll keep trying.

Any secrets?

I hate that sticky stuff guys put on them. In really cold weather you can't get them out of the tank. One time I landed for fuel -10F and I could not get the cap off. I had to put the plane in a heated hanger to get them to work.

RudiGreyling · #6 03-13-2008, 01:01 AM

Quote:

Originally Posted by Mel

They ARE water tight when adjusted properly. 15 years, no water!

OK, please teach us newbies HOW to adjust just right, thanks
Rudi

Mel · #7 03-13-2008, 07:38 AM

Coat the O-rings with a little grease. I use lubriplate. Others use fuel lube.

DGlaeser · #8 03-13-2008, 08:12 AM

If your caps leak, you may have to tweak the compression of the O ring:
- loosen the lock nut
- hold the tab and rotate the bottom disk (as required)
- snug the locknut when you are satisfied with the fit
I disassembled my caps for painting, and when I reassembled them I used the following criteria:
- Close the tab and try to insert the cap - it should NOT fit
- Open the tab, push down to relieve pressure on the O ring - it should fit
- The tab should close with the cap in place without excessive pressure
Now when I open the tab, I have to push down to relieve pressure on the O ring and the cap removes easily.
I'm confident my caps are sealed because when I drained the tanks for my Wt&Bal, I put my finger over the vent opening and within a few seconds the draining stopped. That memory will cause me to religiously check those openings during preflight

kiwipete · #9 03-14-2008, 03:44 AM

Would someone mind posting a link where to get the roll pins from as I've broken one.

Thanks

Peter

hevansrv7a · #10 03-14-2008, 04:39 PM

Quote:

Originally Posted by kiwipete

Would someone mind posting a link where to get the roll pins from as I've broken one.

Thanks

Peter

Someone above mentioned NAPA. I used a 1/16" drill bit shank, cut down with a grinder. I just go two pins from Van's today (they have all the parts) and the were not rolled pins but solid as far as I can tell. I thought the one I broke was a rolled pin, though.