Sign in to follow this  
Followers 0

Gas caps

25 posts in this topic

Posted

I have been through several sets of caps. When I first got this plane, they guy that had been flying it for 250 hrs before me never saw the service bulletin from Avid and never did the mod to put the goose neck vent lines in the gas caps. When I was rebuilding the plane, I did the mod using structural adhesive per the S.B. Since that time, I ahve built 3 different sets of caps using various epoxy's and glues found at auto parts stores for fixing gas tanks etc. None have lasted very long and in short order, they allow the fuel to seep inbetween the aliminum tube and the cap and it vents out across the top of the wing until the fuel level gets below the tubing. Last week when I took off with full tanks, I watched the fuel trailing off the wing for an hour until I burned / leaked enough fuel out of the left tank to get it below the level of the cap sticking into the tank.

So.... What caps are you guys using, and are you using the goose neck vent tube? What are you using to glue the tubes into the cap? Are you having any issue with fuel leaking out with full tanks?

70% of the time I dont have full tanks for the shorter local flights. But when I head up to the lodge I top off so I can get there and back and play around a bit while I am there.

:BC:

Share this post


Link to post
Share on other sites

Posted

I have been through several sets of caps. When I first got this plane, they guy that had been flying it for 250 hrs before me never saw the service bulletin from Avid and never did the mod to put the goose neck vent lines in the gas caps. When I was rebuilding the plane, I did the mod using structural adhesive per the S.B. Since that time, I ahve built 3 different sets of caps using various epoxy's and glues found at auto parts stores for fixing gas tanks etc. None have lasted very long and in short order, they allow the fuel to seep inbetween the aliminum tube and the cap and it vents out across the top of the wing until the fuel level gets below the tubing. Last week when I took off with full tanks, I watched the fuel trailing off the wing for an hour until I burned / leaked enough fuel out of the left tank to get it below the level of the cap sticking into the tank.

So.... What caps are you guys using, and are you using the goose neck vent tube? What are you using to glue the tubes into the cap? Are you having any issue with fuel leaking out with full tanks?

70% of the time I dont have full tanks for the shorter local flights. But when I head up to the lodge I top off so I can get there and back and play around a bit while I am there.

:BC:/>

I used JB weld on my vent tubes,they are vented caps and have a little pin hole on top,I drilled through that hole but not clear thru the whole cap.Thats what Skyraider told me to do. You are still using the vent in the cap with just an extension of the vent hole.I have seen others with the tube clear thru the cap and they told me not to do that.When you turn my caps upside down you don't see the tube on the inside.Randy

Share this post


Link to post
Share on other sites

Posted (edited)

I used JB weld on my vent tubes,they are vented caps and have a little pin hole on top,I drilled through that hole but not clear thru the whole cap.Thats what Skyraider told me to do. You are still using the vent in the cap with just an extension of the vent hole.I have seen others with the tube clear thru the cap and they told me not to do that.When you turn my caps upside down you don't see the tube on the inside.Randy

Now that our Govmt is protecting us from "bad air", the auto systems have unvented caps - This is the ones to use - You can buy a plain one with the handle sticking up from the top, or get the nice chome ones that look pretty and cost more, and the new gaskets are OK with ethenol.

Being somewhat inventive (might say lazy), I looked for a way to have vent tubes ready made, and finally found a cheap substitute for the homemade ones - I got some sconces at Goodwill for $1 each - these are the ones that have the light socket mounted on a 3/8 diameter gooseneck pipe, which has about 3/8 inch threads on each end, and a nut to hold them to the wall plate - If you want a better looking end, then grind the threads off of the end that sticks out - these are about 4 inches tall - guess you could flair the end? If you find ones with the cheap tin nut, then look at places that have lamp parts and buy some better nuts that fit. Use epoxy or Loctite or some kind of sealer to make sure the nut inside the cap stays tight. If you have the caps with the handle, then put the tube off center. You may have room to put a neoprene washer under the nut.

Or, make your own?

ED in MO

Edited by Ed In Missouri

Share this post


Link to post
Share on other sites

Posted

Ed,

I think you may have the metal caps that look like the caps for a PA18 or any of the old pipers. The kit fox caps are like that. These Avid caps use the screw in style caps that are found on the newer trucks.

Randy,

Good idea on not running the tube all the way through, that may do the trick. I was just going off the Avid S.B. and making it the way they showed.

:BC:

Share this post


Link to post
Share on other sites

Posted (edited)

Ed,

I think you may have the metal caps that look like the caps for a PA18 or any of the old pipers. The kit fox caps are like that. These Avid caps use the screw in style caps that are found on the newer trucks.

:BC:/>/>/>/>/>

What is the world coming to? You mean the trucks now have PLASTIC CAPS? God help us J3 drivers!!!!!!!

But, couldnt you use the metal tubes bolted thru the plastic caps?

Maybe look for Chinese sconces with plastic parts? :lol:

ED in MO

Edited by Ed In Missouri

Share this post


Link to post
Share on other sites

Posted

Friend here got sick of the glue failures too, ended up brazing steel vent tubes to his steel caps.

Share this post


Link to post
Share on other sites

Posted

Friend here got sick of the glue failures too, ended up brazing steel vent tubes to his steel caps.

Doug,

Was that on Avid tanks? If so, can you find out what cap he used?? I would love to find steel caps I could braze the vents into like the early KF tanks were.

:BC:

Share this post


Link to post
Share on other sites

Posted

I have plastic auto caps with the vent tubes JB welded in. They leak a little when I full tanks but not bad. The issue I have is if you overtighten the caps to the point they click the vent tube breaks loose. I have re glued them a ton of times. It works but far from ideal.

Share this post


Link to post
Share on other sites

Posted (edited)

I glued in my vent tubes with some old Scotch Weld 2216 that came with my Kitfox project. I had bought a 5 lb kit of Hysol when I rebuilt my Avid MK IV, and the stuff went bad in about a year. The Scotch Weld is at least 20 years old and it still works fine. I wouldn't glue a structrual part with it, but I've glued all sorts of things and it just works fine. Even glued the side rails on a big truck radiator and it's still holding. It doesn't seem to be affected by the gas either. I never had any fuel come out of my vents, but the bottom of the stem just barely goes through the cap. If that end isn't into the fuel how can it suck the fuel up. Also I thought that the idea of the vent tubes facing forward was so air could come into the tanks to give some positive pressure. Maybe I'm not understanding your question correctly??? Take care, Jim Chuk

PS wish the Scotch Weld wasn't mixed 2 parts to 3, it would be the perfect adhesive if it was 1-1

PSS should have mentioned, I have the original metal Avid caps.

I have plastic auto caps with the vent tubes JB welded in. They leak a little when I full tanks but not bad. The issue I have is if you overtighten the caps to the point they click the vent tube breaks loose. I have re glued them a ton of times. It works but far from ideal.

Edited by Jim Chuk

Share this post


Link to post
Share on other sites

Posted

Leni - standard Avid caps I think. Actually, I thought all Avid caps were metal?

Share this post


Link to post
Share on other sites

Posted (edited)

Leni,

would it be possible to drill and tap the plastic caps for 1/8 pipe fittings with the flair, so you could attach a tube to it, or use a fitting and solder the tube to it, and use the fuel-safe stuff that Kitfox uses for fittings? RTV-9, or something like that? isnt the Hysol 9460 fuel proof?

ED in MO

Edited by Ed In Missouri

Share this post


Link to post
Share on other sites

Posted

I think the issue may be that I have the Stant self venting caps that I then drilled out and put the vent tubes into it. When the tanks are full, the gas level is above the threads that are sticking down into the tank. With the ram air pressure the tanks are pressuring up and its blowing the gas out around the vents in the cap lid. When you drill the cap out, it takes out the one way valve in the cap that allows air in, but not out. Maybe I should look for a NON venting cap and try that. The other option is to keep regluing the vent tube.

If anyone has a picture of the Avid metal cap, please post it up and I will see if I can find a replacement cap at the local parts house.

:BC:

Share this post


Link to post
Share on other sites

Posted (edited)

CAC plastics in wasilla sells an epoxy that holds up under fuel. I had a CAN AM 800 that developed a leak in the fuel pump housing. The plate was made of plastic. The name of the epoxy is Westsystems G-flex. My fuel pump repair has lasted with the repair being submursed in fuel. No doubt it would hold up to fuel splashing against it on a fuel cap.

I would like to see a picture of the type of fuel cap you are talking about. Does Airdale sell the caps with the vent tube?

Thanks

Edited by Avid Heavy

Share this post


Link to post
Share on other sites

Posted (edited)

CAC plastics in wasilla sells an epoxy that holds up under fuel. I had a CAN AM 800 that developed a leak in the fuel pump housing. The plate was made of plastic. The name of the epoxy is Westsystems G-flex. My fuel pump repair has lasted with the repair being submursed in fuel. No doubt it would hold up to fuel splashing against it on a fuel cap.

I would like to see a picture of the type of fuel cap you are talking about. Does Airdale sell the caps with the vent tube?

Thanks

West Marine used to be in Anchorage - all the West products were available there., or online.

And, there was a place, I believe, to the east of downtown, on 3rd or 4th, that make cowlings, wing tips, other parts, and I bought the West epoxy there.

ED in MO

Edited by Ed In Missouri

Share this post


Link to post
Share on other sites

Posted

I have one of each type of caps on my plane. I think Avid must have switched from the metal cap type that has two tabs that go in the two cutouts in the filler neck and it turns about 5/8 of a turn. The other tank has the screw in plastic cap with the screw in neck. I was having trouble with the glue coming loose too but can't remember what I used to reglue them many years ago now, but it was a gas resistant epoxy. I had the same problem that Joey described if I turned the plastic cap until it clicked so I stuck the vent tube all the way throught to the inside about 1/4" or a little more and then drilled it for a cotter pin and put an o ring, washer and the cotter pin beneath the washer. That seals off around the vent tube at the bottom but still allows you to glue it solid on the top and turn it past the clicks if you have to. I generally try not to click it any more though, just put it on until the vent points forward.

Share this post


Link to post
Share on other sites

Posted

I took a few pictures today of the gas caps on my MK IV, and also some on a C model that I picked up as a project. They are different, MK IV are metal, C model are plastic and have threads to screw them in. Whipost-329-13552899356161_thumb.jpgpost-329-13552899552583_thumb.jpgpost-329-13552899751758_thumb.jpgpost-329-13552899990611_thumb.jpgch style do you have Leni? Take care, Jim Chuk

If anyone has a picture of the Avid metal cap, please post it up and I will see if I can find a replacement cap at the local parts house.

:BC:/>

Share this post


Link to post
Share on other sites

Posted

I took a few pictures today of the gas caps on my MK IV, and also some on a C model that I picked up as a project. They are different, MK IV are metal, C model are plastic and have threads to screw them in. Whipost-329-13552899356161_thumb.jpgpost-329-13552899552583_thumb.jpgpost-329-13552899751758_thumb.jpgpost-329-13552899990611_thumb.jpgch style do you have Leni? Take care, Jim Chuk

Dont see how these can interchange - the metal ones have ears like the Kitfoxes, and I buy them at Auto stores.

They are also like the $130 Piper caps that I buy for about $10 and put my own tubes on them.

ED in MO

Share this post


Link to post
Share on other sites

Posted

Ed, I didn't say they were interchangeable. They came from different models of Avids. The plastic cap was on a C model, and the metal one was on a MK IV. The plastic ones do stick down into the tank much further than the metal one does, so maybe that is what Leni has. I couldn't understand how fuel could come out of his tanks, but I was thinking about how my metal caps fit into the tank. Take care, Jim Chuk

Dont see how these can interchange - the metal ones have ears like the Kitfoxes, and I buy them at Auto stores.

They are also like the $130 Piper caps that I buy for about $10 and put my own tubes on them.

ED in MO

Share this post


Link to post
Share on other sites

Posted

I have the C model ones. When you drill them out and put the tubes in them, if the glue joint breaks around the tube inside the tank, it will let fuel seep into the cap and leak out around the "self vent" in the caps when the tanks are full. I guess the answer is to make sure and re-glue them when they do break loose.

Thanks for the Pics Jim, that showes exactly what I was talking about.

On another note.. Are any of you guys running that style cap without having drilled them and put the tubes in? The guy that had my plane originally never put the vent tubes in the caps and had 228 trouble free hours, but during my rebuild, I put them in per the service letter from Avid.

:BC:

Share this post


Link to post
Share on other sites

Posted

Gas Caps. The top of the wing is a low pressure zone. We can all agree on that. That, in part, is why the airplane flies.

A vented cap (without a pitot tube on it) will vent into this low pressure zone making the gravity feed of fuel over come that low pressure to feed to the system. To me, at face value, this is not an optimal situation.

Once a pitot tube is added to the cap, you actually pressurize (very slightly I admit) the top of the tank forcing fuel into the system.

Certified planes, to the best of my knowledge, don't vent to the top of the wing, through the cap. They vent to an alternate location.

IMO, using an unmodified automotive vented cap, on the top of the wing, is an invitation for disaster.

Share this post


Link to post
Share on other sites

Posted (edited)

Gas Caps. The top of the wing is a low pressure zone. We can all agree on that. That, in part, is why the airplane flies.

A vented cap (without a pitot tube on it) will vent into this low pressure zone making the gravity feed of fuel over come that low pressure to feed to the system. To me, at face value, this is not an optimal situation.

Once a pitot tube is added to the cap, you actually pressurize (very slightly I admit) the top of the tank forcing fuel into the system.

Certified planes, to the best of my knowledge, don't vent to the top of the wing, through the cap. They vent to an alternate location.

IMO, using an unmodified automotive vented cap, on the top of the wing, is an invitation for disaster.

Got to disagree a little here - check out the Spruce catalog - the Piper, Luscombe, and others have the vent tubes on top of the caps - and they sell for over $100 each!

An UNVENTED auto cap - with the tubes added - is what you need to prevent fuel leakage when wings are folded.

I have a set of original Piper J3 caps if you cant find a photo.

Yes, there are other "certified" planes with internal, overflow, vent tubes, but these do not pressurize the tanks like the cap tubes.

ED in MO

Edited by Ed In Missouri

Share this post


Link to post
Share on other sites

Posted

I don't have any knowledge to disagree on the cert planes completely, Ed. Only the Cessnas and pipers that I have flown all were not vented to the cap.

What I do know and what I have seen is that these airplanes will siphon a tank dry if the cap does not seal and vent properly. My friend Jim took off in his Kitfox IV neglecting to reattach his caps properly. Within 10 minutes both caps were gone and all of his fuel was siphoned out causing an off airport dead stick landing.

Share this post


Link to post
Share on other sites

Posted

PA-28s I learned in had the sealed 2-tang metal caps, non-vented. I gotta agree with Larry that omitting the pitot tube on our caps is a poor idea. What I did learn in this thread thanks to Jim's pics is that there was a diff in caps between the Avid C and Mk-IV models. I had never seen the threaded plastic caps before. BTW, my Avid+ oem wing tanks came with 2-tang metal caps and D.I.Y. pitot tubes.

Share this post


Link to post
Share on other sites

Posted

I have seen them both ways on the Pipers. The pacer has caps with tiny holes drilled in them to vent. The PA 12 I have been flying has solid caps and I am not sure how they vent. You can get the Atlee Dodge caps that have the pitot type tube in them.

I was flying high cover one day for a guy that was picking some hunters up off the side of a mountain by Lake Clark. He had pulled 3 of the 5 people off the mountain and we stopped at Port Alsworth for gas. He left one of the caps sitting on top of the wing and within 5 minutes after take off his left tank was bone dry. I saw the fuel getting sucked out as I passed over the top of him about 2 minutes after take off and it was not just slopping out of the tank, it was coming out like a tornado was sucking on it! As soon as I alerted him he flipped a bitch in record time and headed back for the strip.

I think I will find the unvented auto caps and try again to get the glue to seal the tubes up in them. I just hate not being able to top off for long trips, or know exactly how much gas is left onboard because it went out the cap instead of through the flow meter.

:BC:

Share this post


Link to post
Share on other sites

Posted (edited)

I have seen them both ways on the Pipers. The pacer has caps with tiny holes drilled in them to vent. The PA 12 I have been flying has solid caps and I am not sure how they vent. You can get the Atlee Dodge caps that have the pitot type tube in them.

I was flying high cover one day for a guy that was picking some hunters up off the side of a mountain by Lake Clark. He had pulled 3 of the 5 people off the mountain and we stopped at Port Alsworth for gas. He left one of the caps sitting on top of the wing and within 5 minutes after take off his left tank was bone dry. I saw the fuel getting sucked out as I passed over the top of him about 2 minutes after take off and it was not just slopping out of the tank, it was coming out like a tornado was sucking on it! As soon as I alerted him he flipped a bitch in record time and headed back for the strip.

I think I will find the unvented auto caps and try again to get the glue to seal the tubes up in them. I just hate not being able to top off for long trips, or know exactly how much gas is left onboard because it went out the cap instead of through the flow meter.

:BC:/>/>

Back in the days of "Full Service", when gas stations washed your windsheild, checked the tires, etc, you always had to check the caps because if the line boy put them on backward, the vent tube would suck your gas out - Now that we are all doing "self-serv", we shouldnt have that problem.

ED in MO

Edited by Ed In Missouri

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0