Fuel cap O-rings

[kestrel]

It is time for me to make my fuel caps less cantankerous. A while back, based on something I had read, I put fuel lube on the O-rings. Worked great! ...for a while. Then the fuel lube got all sticky and stiff. Now I'm looking for advice. I'm not going to make it through the cold weather of winter as they are now.

- Re-apply fresh fuel lube?
- Clean them somehow? (fuel lube seems permanent?)
- Install fresh O-rings (mine or original, first flown in 2006, kit from a few years before that.)

This post is mostly asking where to buy the O-rings? Does Mark sell them separate from the full fuel cap assembly? However, it occurs to me that someone here may feel they have a better idea than new O-rings.

Thanks!
Ty

[jaredyates]

Calling all Kevins! Guest

[swpilot3]

I'm ready to buy if Kevin is ready to sell. :-)

[Collin Campbell]

Mark sells the O-rings I believe. Bob recommends using fuel lube on the aluminum threaded parts of the cap to prevent galling and a just a few drops of motor oil on the O-rings from time to time. Collin

[kestrel]

I'll try some oil first and then contact Mark if that doesn't work. Thanks!

[Nev]

Did you resolve this issue ?

[Bcone1381]

My cap is tight to remove. I don't like to pry it with a tool, but how else can I get it out?

I've lube it with engine oil. I've removed .005 to .010" of material from cap's the O-ring face that the ring fits around and have a loose fit on the cap. I found even a touch of Fuel-Lube (E-Z Turn) on the rings to be unsatisfactory because it behaves like a greased pig when I tighten it down....slick!!

I've determined that the O-rings in the relaxed state are too big. My tank hole is 1.750. The o-rings are a wee bit larger. I checked out O-rings on McMaster-carr; DASH 324 size o-ring with an OD listed as 1.770" fits Bob's drawing dimensions. So I suspect that is my O-ring dimension----- twenty thousandths oversize.

The next size down (Dash 323) has an ID .062 smaller and has the same 3/16" cross section. I will try that. I'm hoping it will be snug around the cap, require no lubricant, easy to remove when dry, and ring expansion able to provide a secure fit when it's tightened down. We'll see. This is experimental aviation.

New rings are in the mail. I ordered extra. If they fit, I'll bring the extras to OSH.

[Mark Goldberg]

Per Bob - lubricating the o rings is part of how they were designed and intended to be used. Mark

[Bcone1381]

Thanks Mark, I knew that once upon a time.

I looked it up again in Beartracks and Bearhawk.tips to refresh my memory. Beartracks Apr 2000, and Patrol Newsletter Dec 2006 p.3 say to lubricate the threads. Jul 2010 expands on this......O-rings get lubricated with Engine Oil or Bearing Grease every few fueling events, while Bob's suggested Threads (NOT O-rings) lubricant is E-Z Turn (Fuel Lube).

[Battson]

Lubricating O-rings with anything non-soluble in fuel will cause them to come out mid-flight in certain circumstances. Mine have never been lubricated with anything except AVGAS, and even that is not necessary unless it is very cold.

If the caps are too tight and difficult to remove, then they are not a good fit with the tank filler neck - and need to be modified.

[Utah-Jay]

Please report on the fit when you make a determination

[Bcone1381]

The new O-ring, (Dash 323) was installed this morning. Bottom line, I like this better, and believe it improves my cap. The longer story...

My Patrol is under construction since 2017. Before this morning the caps were tight enough to create a barrier to me to want to remove them. Even after machining down the cylinder that the o-rings surround from 1.360 to 1.355 (see attachment), I often used a putty knife to help pry them out. Yet they had been installed for a year or more.

Today the cap with the new Dash 323 O-ring installed has a outside dimension .008” smaller. It fits into the filler neck with a feel similar to the old o-rings (not loose, snug but not too snug). Removal after it’s been tightened is much improved. While pulling up on the cap, I gently rock the cap back and forth 2-3 times to remove it. I did not need a putty knife or other tool to remove it.

I believe I will have a secure cap when tightened properly. The risk we need to be aware of is…will the smaller o-ring be less secured when tight than the larger one. Check yours. Mine has sufficient O-ring expansion when tightened to lock it in place, maybe without grease or oil. I feel better about that.

Three sets of these will be with me at OSH. Contact me if you are interested.

Screen Shot 2022-07-02 at 9.27.18 AM.png

[Richard E]

I have reduced o ring size and fitted a roller pin as recommended by Nev on www.bearhawkblog.com and it works brilliantly. No need for a screwdriver any more and they lock securely. Good advice Nev. Thank you.

[Nev]

Great to hear Richard!

[Battson]

It should be noted in this thread; the filler necks material (tube stock) were found to vary in size, due to an issue with tolerances in the materials. That variability in filler neck size has made some Bearhawk fuel caps much more difficult to use than was intended by the designer. This issue has been resolved for any new factory tanks, so will not concern new buyers.

If a Bearhawk owner has gas caps that don't fit well, I would encourage them to get the problem resolved by either resizing the cap metal parts, or O-rings, as desired. Refer to other threads to learn more about how this works.

The bottom line, the Bearhawk fuel tank caps should not be difficult to use.

[Nev]

Very pleased to see you on board with this Jon, much appreciated. This is a great example of collecting data and using it to identify an issue that can then be rectified to improve safety for everyone.