Fuel cap replacement / Shaw Plug / Snap Tite

[RodgerC]

I've had to replace two fuel caps in two years and at >US$50 each plus airfreight to Oz, decided to engineer a permanent solution...The pictured item is machined out of aluminium and uses a replaceable $0.75 Nitrile O-ring that expands from 48-52mm...The over centre cam lever and wear washer are out of one of my failed Shaw Plugs.

Regards
Rodger
Waiex #155 VH-YEX aka KAYOS

[Kirk S]

Quite interesting Roger, fuel in the cockpit streaming down the firewall inside the cockpit while flying is not fun ! Could you post a little more ? Did you cut down on a lathe from a raw 6061 block ? Not sure how you how you expand the o-ring.
TIA, Kirk S. YX 041, 3300 Jab, 727 hrs.

[GordonTurner]

Gorgeous. I'm actually concerned enough about the milk jug stopper arrangement that I'm considering just ordering a new tank before I get to the install phase. At the least plan to install the oops fittings.

Gordon

[RodgerC]

I found the milk jug stopper to be very effective, but short lived...Don't know what sort of nitrile rubber is used, but they become embrittlement and crack in short time...By the time freight to Oz is added, the Shaw Plugs cost more than $100/each and that is eating into my maintenance budget. The plug uses a 1 1/2" ID x 3/16 O-ring that is expanded on the 30deg (60deg included) taper. It was machined from a piece of 6061 bar. A cap screw shaft is sealed in the lower tapered section with a small o-ring under its head. It was turned up by my brother-in-law, so I can't take credit for the workmanship but it works exceptionally well.

[sonex892.]

I found the milk jug stopper to be very effective, but short lived...Don't know what sort of nitrile rubber is used, but they become embrittlement and crack in short time...By the time freight to Oz is added, the Shaw Plugs cost more than $100/each and that is eating into my maintenance budget. The plug uses a 1 1/2" ID x 3/16 O-ring that is expanded on the 30deg (60deg included) taper. It was machined from a piece of 6061 bar. A cap screw shaft is sealed in the lower tapered section with a small o-ring under its head. It was turned up by my brother-in-law, so I can't take credit for the workmanship but it works exceptionally well.

I did the same as Roger for my aux fuel tank. I too used the metal parts from the shaw plug. I just copied the idea from some wing tank caps I had bought.

My first Shaw plug rubber didnt even last 1 year, it split at the bottom washer. I think I may have been over tightening it. I still use the standard rubber plug in the main tank. It's now lasted 5 years. If and when it breaks I will turn down another and use the O ring type.

Steve
Sonex 892
VH-ZSX 3300 192hrs

[DCASonex]

Very nice looking design, much more professional looking than the Thermos bottle stopper. Looks like the bottom part is a cone that slides up and into the O ring to stretch it to seal inside opening rather than by compression. Do you use any lubricant on the cone or O ring ?

Wish you had posted this a couple of weeks ago, just received from Shaw an order of 5 replacement Nitrile rubber parts for the original units. Still may have a go at making one for the better appearance, and perhaps better sealing.

David A.

[RodgerC]

No lube required...Very smooth operation

[DCASonex]

Steve and Roger,

I owe you both double. Having bad case of cabin fever, an adequate supply of raw material, and a decent lathe, decided to have a go at making one of those. I looking at neck of my fuel tank to see just how far down I should locate my o ring, realized that the neck is so short that the inside starts to flair into a radius about 1/8" down. The wine bottle stoppers bulge well below that. No wonder I have had problems getting a decent seal. Only had about 3/32" clear from top of the bottle stopper to underside of fuel door, but found a 3/16" square cross section O ring from an old oil filter, and placed that under rim of one of my bottle stopper caps to raise it to position the bulge more up into the neck. Big improvement. Was able to grinding off enough material from top of the brass cam to still clear the fuel door. Great, but did not cure the cabin fever.

Never being one to leave well enough alone, decided to see what I might do differently for your O ring type fuel cap design. Since was always losing setting and having to re-adjust the wine bottle stopper's screw when filling tank, thought why not just make it screw tight. This of course actually makes design more complicated with need for some means to key the upper and lower halves to prevent rotation, and a tab to prevent entire unit from rotating. Decided to machine the outside tab as part of the top plate, which meant it would look like a frying pan handle and required setup in 4 jaw chuck. (I did mention having cabin fever) Made bottom half which is the forcing cone of Delrin because it is light, has good fuel resistance, and I had a short 2" dia. bar of it. Located center-line of O ring only 7/32" down from top of neck. That was far enough to put it into the beginning of the tanks inside radius so that there was no way tightened cap could be knocked or vibrated out, but not so far in as to require expansion beyond what is achievable with the design. Made 15 degree angled seat on top plate so that it would be pulled down tight to tank as O ring was pushed out by the 60 degree taper on bottom forcing cone. All SS hardware, with small O ring sealing center bolt, and a small screw and washer into top end to keep unit from accidentally being completely unscrewed. Knob is cut down aluminum 4 arm star type, and a small peg on underside of fuel door comes down in large space between arms to insure that knob does not unscrew in flight.

Seems to work. Feels like it seals tight, quick to install or remove, with just two turns of knob (18 threads per inch on center bolt), looks way better than the wine bottle stopper, and weight is about the same. Probably could have done without the frying pan handle, but that also provides a place to tie my cable. (Once taxied away from fuel pump without the cap, now it is tied to plane like mittens on a kid.)

So now have two good working fuel cap options, but like the feel of the way the new O ring unit tightens down, and it just looks more professional.

Thanks again, Now to clean up big mess of aluminum, stainless and Delrin turnings and chips from shop. No flying weather yet, so will see about replacing that old 4 jaw chuck which likely dates from WWII, like my "newer" lathe (old one dates from about 1890, and was also used on small parts of this project.)

David A. Sonex TD #1327, CAE 3300 #0004

[sonex892.]

David
Good to hear you had a win. With the Shaw plug hardware I used on my cap I find there to be a lot of stress on the part when snapping it closed. So I also screw it to tighten and seal.
I just dug out the Usher fuel tank cap kits I had stashed to refresh the memory. Though you might be interested.
They are cast and use teflon on the wedge surfaces. They use a small o ring under the over center latch to stop fuel tracking up the thread.Even though they are chamferred at the top they are also quite shallow and would more than likely fit the older type sonex tank. So may work for people that dont want to make their own. I'll check that out on the next trip to the airport. If it fits ACS have them at $44.85.
http://www.aircraftspruce.com/catalog/a ... shCaps.php
Snap closed in mounting flange

[RodgerC]

David...A more productive way to spend the weekend than vegging out in front of Netflix...Rizzz asked for the drawings today, so we can expect another example in a week or so.