Thorp Air Command - T18.net

Looking for replacement parts for this cap - mainly the black rubber.
Not sure if this same cap is sold /used any longer.

MG

MG-
I think if you search this site or the last one or the old Thorplist, you'll find that many have been down this road before. I can't remember if a solution was ever found. Regarless, I strongly recommend you devise a positive mechanical means of retaining your cap. That type, with the friction lock by expanding rubber, can pop out in a crash. You don't want that to happen.

I replaced mine with a threaded cap and bung.

D

MG : Are there any markings on top of the cap ? It looks like the old style ACS cap ? If it is the old style ACS cap that rubber part is no longer available . A few years back I contacted ACS about buying the rubber portion and they sent me a bag full of them (maybe 10-15 ?) for free . I told them I was part of the World Famous T-18 Flying Circus ! I mailed all of them out to T-18 guys that said they had this cap as ACS said they were phasing out this cap for one that has the Viton rubber O- ring . That is the cap I have on the AC now . Had to enlarge the opening slightly for the new cap and a I carry a spare Viton O ring in my pack up kit . BOOM !

RB

Higher and Faster

Thanks, Dick & Rich - I'm going to look into changing it over to a different type of cap.

Mark

I had the same problem. The rubber on the old caps (aux wing tanks) was so old and stiff that it would not release so you could remove or reinstall the fuel cap. I couldn't find replacements either, and ended up ordering a couple of o-ring fuel caps. It was the "Flush Assembly Cap - E-450-000" from Wag-Aero. The o-ring and middle part of the assembly was the right diameter to seal, but the upper and lower parts/flanges on the cap were a little too large in diameter to fit into the hole. I used my lathe to machine these to slightly smaller diameters, and I'm very happy with the result. The caps seal perfectly, and are easy to open and close.

If you end up doing surgery to your tank, go with a flush cap. My screw-on works ok, but there's not a lot of room for fingers between the cap and the boot cowl. It didn't help that the bung ended up a little off-center with the opening.

D

That's the cap that Ken Brock sold with his tanks for years. It's a modified version of the cap in the plans, fold over lock instead of wing nut. Look at Thorp dwg 1188 for details on the sealing ring, it's straight out of the plans.

I may have a spare laying around.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

The cap in the picture is my spare, have the same on the aircraft.
The rubber on the spare cap is not soft and does'nt hold well when locked.
It's not much of a spare if it doesn't work.

Van has a retrofit flange that you proseal in, with a lock cap.
Not sure if that will work with the existing tank flange.
The ACS new style cap may also work.
I'm checking dimentions.

MG

Please let us know if the retrofit Vans flange will work. I believe it will from the preliminary numbers I got from somebody on the Vans site. I have a fuel cap like the one you posted as well and I want to proseal in the Vans flange if it will fit.

If you have the old ACS flush style cap with the large rubber gasket you may be able to save yourself a lot of work if you go with the "new" ACS cap with the Vitron O-Ring . Only a slight mod was required with my CSA tank . I enlarged the opening ( probably less than 1/32nd of an inch ) , before I installed the tank . I suppose if you can fit in a new flange and new cap that would work ? With the new ACS cap I still have a flush fitting cap .

RB

Higher and Faster

I replaced the old style cap with the Aircraft Spruce viton one that Rich mentioned. With the tank installed it's hard to accurately increase the inside diameter of the tank flange. Instead, all you need to do is disassemble the cap and sand the outer circumference of the aluminum cap at its largest diameter until it fits in the countersunk part of the tank flange. Fit the cap in upside down to test if you have sanded enough. Once it fits this way, flip it right side up to see if the stepped portion of the cap fits the smallest inside diameter portion of the tank flange. If it won't drop in, the smaller stepped portion of the cap will need sanding also. Both areas that you sanded are not critical to keep perfectly round as the o-ring seals against the bottom of the undisturbed tank flange and the beveled portion of the cap which expands the o-ring. Reassemble and see if it fits in. Had to sand off maybe 1/16" on largest outside edge and just a few thousands of an inch on stepped portion of cap to get it to fit. Pretty quick and easy.
If you have a lathe it would be quicker and a little more accurate, but wasn't necessary on mine.

The cap is ACS #10455 (part number 05-01391) from Spruce for $39.95. I put mine in years ago but this looks like the same cap I have.

Hope this makes sense.


Bernie Fried
N18XS

Hey Bernie, I appreciate that part #. I just bought one and I'm going to try and use your directions. Thanks.

If possible, attach some pictures.

thanks,
MG

Bernie
I just got my fuel cap and took it to a machine shop. They put it on a lathe and reduced the diameter of the top and bottom rings as you described (for $20!). The only problem now is that the Viton o-ring is too large to fit in the opening. Did you have that problem also? If so, how did you reduce the diameter of the o-ring?

We have an aviation supply here on the field LAL. They carry a large assortment of rings, maybe go this route. Also buy some grease that is gasoline resistant. It will make the O ring seat better. I have found grease at NAPA