Yooper Rocketman Posted April 2, 2015 Report Posted April 2, 2015 During my annual this year my A&P and I looked at options to fix a nagging fuel cap removal problem. I have the spring loaded baffles inside the fuel filler neck that must be to keep fuel in the plane when someone is stupid enough to take off without the cap on. When I fly up in the flight levels, the air gets thin enough that the area between the cap and the baffle must reduce to altitude, and then when I get back on the ground, the baffle and cap are so well sealed that I have a vacuum on the cap. Sometimes one of them sticks so bad I need my fuel sump tool with the screwdriver to pop the cap off. I've had times line service has called me asking why the cap won't come off. We thought about drilling a VERY tiny hole (1/32") in the baffle, pulling the little bit of drill shavings away with an air operated vacuum, but it's stainless steel, and that effort put a broken drill bit in the tank. Thanks to luck and a magnet, we were able to retrieve it. I did look inside with a mirror and there is an o-ring in the lower face of the neck that the baffle seals against. I thought about pulling the o-ring and cutting a "nick" in it, but it doesn't look easy to re-install "if" I can even get it out. Anyone else had this issue and have ideas how to cure this nagging problem? Quote
carusoam Posted April 2, 2015 Report Posted April 2, 2015 Misunderstanding of the challenge typed here.... No vacuum is possible unless the vent is blocked. Do you have a picture of the stainless flap? I don't believe that is a Mooney supplied part. Magnet that can pick up a stainless steel part? (Somewhat unusual too) Please know that I'm trying to be helpful, no matter how bad my typing actually is. Best regards, -a- Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 Ah, not you're not reading the problem close enough. There IS NO vent between the cap and the anti-sipon baffle. It's just a small 2" area under the cap. Quote
carusoam Posted April 2, 2015 Report Posted April 2, 2015 I was still writing.... Now, I understand the vacuum is between the flap and the cap? Unfortunately, I'm not familiar with the flap... Questions that come to mind... Is it intended to be a tight seal? What allows it to seal so tightly? - a seal. - some goo. - tightness between surfaces. Best regards, -a- Quote
Hank Posted April 2, 2015 Report Posted April 2, 2015 Give a short squirt of Tri Flow down the center of the cap where the rod goes through to release it on the inside. Work it up and down several times, it should get easier. If no Tri Flow, squirt a dab of LPS White Lithium and let it sit overnight, it will ooze down inside and lubricate the o-ring around the shaft. If it's still tight, you need to disassemble the cap and put a new o-ring in. It's a little one, I don't recall the size but someone here probably knows it if you don't have easy access to a Parts Manual. While you're at it, a little lube on the big o-ring around the edge of the cap never hurts. It's never a bad idea to replace both o-rings in each cap, the little one is just a pain, requiring disassembly to reach. Good luck! Anthony, the broken drill bit wasn't stainless (although 400-series is magnetic, it makes poor drill bits), the stainless flapper broke the drill without getting a hole. Little bitty drill bits need high RPM and a steady hand (like a drill press) to be effective; hand drills are way too slow. Do you have a Dremel? Quote
carusoam Posted April 2, 2015 Report Posted April 2, 2015 I thought we were catching the SS filings with the magnet... Thanks Hank! What is the name of the metal filings? Machine shop guys would know this... Engineer in search of a challenge, Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 I thought we were catching the SS filings with the magnet... Engineer in search of a challenge, -a- If I had known it was stainless, we would not have been trying to drill it. Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 Give a short squirt of Tri Flow down the center of the cap where the rod goes through to release it on the inside. Work it up and down several times, it should get easier. If no Tri Flow, squirt a dab of LPS White Lithium and let it sit overnight, it will ooze down inside and lubricate the o-ring around the shaft. If it's still tight, you need to disassemble the cap and put a new o-ring in. It's a little one, I don't recall the size but someone here probably knows it if you don't have easy access to a Parts Manual. While you're at it, a little lube on the big o-ring around the edge of the cap never hurts. It's never a bad idea to replace both o-rings in each cap, the little one is just a pain, requiring disassembly to reach. Good luck! Anthony, the broken drill bit wasn't stainless (although 400-series is magnetic, it makes poor drill bits), the stainless flapper broke the drill without getting a hole. Little bitty drill bits need high RPM and a steady hand (like a drill press) to be effective; hand drills are way too slow. Do you have a Dremel? The only way that fixes the problem is if the fuel cap will leak air into the chamber. Not a solution I would desire. The whole reason this is a problem is because the seals on the fuel cap are working. Quote
carusoam Posted April 2, 2015 Report Posted April 2, 2015 SS is quite a challenge to drill or cut. It hardens when heated and gets even harder to drill and cut... You get one chance, keep it cool and lubricated... Best regards, -a- Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 Yes, we have done it on my other project, but it requires some skill and patience. We just were not expecting the flapper to be stainless. I have for years called those flappers "dumb shxx" valves, for the dumb shxx that doesn't check his caps during the pre-flight. When I got the Rocket, it had chain lanyards on the fuel caps. That would be something, leave the cap off and have it beat the wing to death before getting back on the ground. Needless to say, those chains were one of the first things removed upon purchase. A replacement cap would be far cheaper than the skin work required from the chain holding the cap on the wing in flight. Quote
DonMuncy Posted April 2, 2015 Report Posted April 2, 2015 My 231 may be defective, but the anti-syphon flap does not seal that tight. Once, I foolishly let the line guys put the caps back on, and on take-off, fuel ran up past the flap and out onto the wing. I figured the flap was to deter, but not necessarily prevent fuel loss. Quote
Hank Posted April 2, 2015 Report Posted April 2, 2015 Seems like it would be fairly easy to grab the flapper with needle nose pliers (jaws all the way across the flapper) and roll your wrist, which should put a shallow bend I. The flapper. Bent flap won't seal tight. The. You'll know if the problem is you flapper, the vent or the orings. Just do one to test. ROLL the pliers, do. It twist lest you tear the flapper off; the pin that holds it in place may not be stainless. Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 Seems like it would be fairly easy to grab the flapper with needle nose pliers (jaws all the way across the flapper) and roll your wrist, which should put a shallow bend I. The flapper. Bent flap won't seal tight. The. You'll know if the problem is you flapper, the vent or the orings. Just do one to test. ROLL the pliers, do. It twist lest you tear the flapper off; the pin that holds it in place may not be stainless. Hank, I thought about that, but since the flapper overlaps the bottom of the filler neck, I would need to get my hand down inside the fuel tank. With tendinitis in both my wrists from way too many hours on the working side of hand sanding tools, there is no way I could do that. Unless something else comes up from another Mooniac, I will likely take a notch out of the o-ring. I clearly know the problem is not a vent, as there is no vent between the cap and the flapper plate. I will try to ge a picture of this set up tomorrow. I had no clue that most K models and newer didn't all have this option. Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 My 231 may be defective, but the anti-syphon flap does not seal that tight. Once, I foolishly let the line guys put the caps back on, and on take-off, fuel ran up past the flap and out onto the wing. I figured the flap was to deter, but not necessarily prevent fuel loss. Don, Good to know. Not sure why this issue has only come up over the last several years, as I have owned this bird for 14 years. Quote
Hank Posted April 2, 2015 Report Posted April 2, 2015 Hank, I thought about that, but since the flapper overlaps the bottom of the filler neck, I would need to get my hand down inside the fuel tank. With tendinitis in both my wrists from way too many hours on the working side of hand sanding tools, there is no way I could do that. Unless something else comes up from another Mooniac, I will likely take a notch out of the o-ring. I clearly know the problem is not a vent, as there is no vent between the cap and the flapper plate. I will try to ge a picture of this set up tomorrow. I had no clue that most K models and newer didn't all have this option. Would bent-tip needle nose fit inside the opening? Quote
N201MKTurbo Posted April 2, 2015 Report Posted April 2, 2015 Just remove the oring on the fuel cap shaft. It should break the vacuum. Quote
chrisk Posted April 2, 2015 Report Posted April 2, 2015 I have this issue on my 231. It only happens if I fill the tank to the very top. Filled to the point fuel runs out when I put the cap on. Just put less fuel in unless you really need it. You'll save time at the pump too. Quote
carusoam Posted April 2, 2015 Report Posted April 2, 2015 Quick review of the challenge... (1) the seals on the cap seem to be working really well. (2) the sealing of the flapper seems to be somewhat unique, as only one other person has mentioned it... (3) a bend in the flapper or even a deep scratch or two would relieve the vacuum of such a small volume. (4) three people, all M20K owners, have the flapper. (5) the flapper is stainless steel and hard to drill. (6) the vacuum does not involve the rest of the tank. The vents are in working order. To prove the theory of the flapper actually sealing... Consider placing a piece of line or wire, attached to the cap where the chain belongs... Running the small wire between the flap and the sealing surface will prevent the vacuum from building in the small volume that the OP describes. If the problem persists with a wire in the way, check the vents for blockage. Best regards, -a- Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 I have this issue on my 231. It only happens if I fill the tank to the very top. Filled to the point fuel runs out when I put the cap on. Just put less fuel in unless you really need it. You'll save time at the pump too. I don't fill it to the top often, but when the fuel pricing is good, and I use Airnav for all cross country flights, I top it off. Before extended range tanks were installed, almost every flight required careful fueling to ensure a good top off. When I dropped the Rocket off in Salina, KS (2001) for the TKS install, I gave explicit fueling instructions to the FBO. When I returned a month later to pick it up, they had only fueled to the bottom of the filler neck. I called them over, (different business than Cav Aerospace)and told them to finish fueling the plane. They were not happy, but installed another 8.5 gallons, which was just enough to allow for a non stop flight back to the U.P. That 8 gallons has to be fueled slow, as you need the vents to allow the air to come out of the tank. It can't vent out the filler neck due to the stupid baffles. Quote
carusoam Posted April 2, 2015 Report Posted April 2, 2015 Talking baffles and venting... Os have a long V notch in the fuel neck (aka baffle?) where Ss don't... Some hangar elves or pixies have drilled vent holes in those things too to provide enhanced refueling... There are pictures around here for that... Tom, when you get a chance, your NJ hasn't been filled in...consider flying out for a NJMOONEY fly in. Best regards, -a- Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 Talking baffles and venting... Os have a long V notch in the fuel neck (aka baffle?) where Ss don't... Some hangar elves or pixies have drilled vent holes in those things too to provide enhanced refueling... There are pictures around here for that... Tom, when you get a chance, your NJ hasn't been filled in...consider flying out for a NJMOONEY fly in. Best regards, -a- Ok, you lost me on that one? NJ ? Quote
Guest Posted April 2, 2015 Report Posted April 2, 2015 Just remove the oring on the fuel cap shaft. It should break the vacuum. Removing the O ring would be contrary to SB M20-229A and would allow direct water entry to the tank throught the centre bore of the cap. Clarence Quote
Hank Posted April 2, 2015 Report Posted April 2, 2015 Yooper, I can't quote this morning, it may be time to reboot. Anthony is commenting on the map in your signature. Go visit the NJ Mooney Pilots and fill in that embarrassing white spot . . . You may get the opportunity to admire some hangar elves' work on fuel necks while you are there, and if you eat long enough they may visit you, too. 1 Quote
Yooper Rocketman Posted April 2, 2015 Author Report Posted April 2, 2015 Yooper, I can't quote this morning, it may be time to reboot. Anthony is commenting on the map in your signature. Go visit the NJ Mooney Pilots and fill in that embarrassing white spot . . . You may get the opportunity to admire some hangar elves' work on fuel necks while you are there, and if you eat long enough they may visit you, too. Ok, got it. Been there, lived in Havre DeGrace (sic?) just outside of Baltimore back in 74/75 while stationed at Aberdeen Proving Grounds and toured a bunch of states while there. Just never made it there in my own plane yet. That's a pretty serious flight to just fill in a blank, but then 3 of the 4 states in the Continental US I have not visited are in the East (RI, NH and VT). Quote
N201MKTurbo Posted April 2, 2015 Report Posted April 2, 2015 You are correct Clarence.... Didn't think about water, we have so little of it around here. Quote
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