Fuel cap getting difficult to close

[WaynePierce]

One of my fuel caps is becoming harder to push the "flipper" back in to position after it's been taken off. Is this something that can be repaired? The O rings are in good shape and I can see any type of damage that would cause it to be stiff getting pushed back down, any ideas? WD-40? or something similar? Any experience with this? 1985 M20J

[ArtVandelay]

Take it apart and lube it, I use EZ turn because it’s  fuel resistant.

[Hank]

Open the flap, squirter a dab of LPS lithium grease or Tri Flow in the center. Open and close flap several times. This will lubricate the little oring in the middle.

If you still have trouble, take it apart and replace the little bitty oring in the middle. Then lubricate it periodically. 

[N201MKTurbo]

I check the o-rings and lube the caps at every annual. Well at every phase 2 inspection nowadays.

[WaynePierce]

13 minutes ago, N201MKTurbo said:

Well at every phase 2 inspection nowadays.

Is that what an annual is being called these days? Kind of like our BFR has gone the way of the dodo bird?

[DCarlton]

Like everyone has said, lube it or take it apart, clean it and lube it.  I finally took mine apart after fussing with them for a couple of years.  Cleaned the corrosion off the pins, buffed the pitted metal (the contact area of the cam thing), replaced o-rings and lubed; much nicer now.  I also bought a third one to keep as a spare.  

BTW, would like to fly into KOLV one day.  Originally from MS.  Had a friend that used to work as a CFI out of KOLV.  Heard it's a nice airport for GA.  

Edited June 21, 2022 by DCarlton

[Fly Boomer]

23 minutes ago, DCarlton said:

I also bought a third one to keep as a spare.  

Me too (fifth one).

[N201MKTurbo]

1 hour ago, WaynePierce said:

Is that what an annual is being called these days? Kind of like our BFR has gone the way of the dodo bird?

No, I have a progressive maintenance plan for the Mooney. I don’t do annuals anymore. The airframe inspections are in phase two.

[WaynePierce]

1 hour ago, DCarlton said:

Like everyone has said, lube it or take it apart, clean it and lube it.  I finally took mine apart after fussing with them for a couple of years.  Cleaned the corrosion off the pins, buffed the pitted metal (the contact area of the cam thing), replaced o-rings and lubed; much nicer now.  I also bought a third one to keep as a spare.  

BTW, would like to fly into KOLV one day.  Originally from MS.  Had a friend that used to work as a CFI out of KOLV.  Heard it's a nice airport for GA.  

There are a number of really GA friendly airports in the Memphis area. KOLV is definitely one of them!

[FlyingScot]

This might be of assistance - I change these every year, and lube every month. Courtesy of our friends at BeechTalk.

O-Ring Change on Shaw 531 Gas Capa.pdf

[WaynePierce]

1 hour ago, FlyingScot said:

This might be of assistance - I change these every year, and lube every month. Courtesy of our friends at BeechTalk.

O-Ring Change on Shaw 531 Gas Capa.pdf 395.94 kB · 5 downloads

This is extremely helpful, thank you!

Where do you go in NC? That and the Panhandle of Florida are my main destinations... Greensboro in NC.

[Guest]

You guys do know that Mooney has an SB covering fuel cap O rings right?  Search the Mooney website for SB M20-229A and support a shop that stocks O rings.

Clarence

[Andy95W]

IIRC, Don Maxwell (or maybe Paul Loewen) suggested letting a drop of oil drip from the engine dipstick every now and then and exercise the cap mechanism.

[StevenL757]

23 hours ago, Andy95W said:

IIRC, Don Maxwell (or maybe Paul Loewen) suggested letting a drop of oil drip from the engine dipstick every now and then and exercise the cap mechanism.

Adding @WaynePierce

A bit surprised Don would recommend that...or anyone for that matter.  I'm sure you "can" use oil, but I believe Tri-flow is the recommended lubricant for your fuel cap internal workings.

I'm also surprised no one mentioned setting the proper tensions on the fuel cap levers after reassembly, and before securing the cotter pin.  The tensions should be snug-enough to provide a nice tight seal, but not so tight that it hurts your fingers while trying to clamp the lever down or release it.  There should be somewhat of a "detent" at about the 45-degree position when the lever is moved down from vertical that is prominent, yet firm, and then closure from there is snug.

[KSMooniac]

I'm pretty sure the maintenance manual calls out general purpose oil, not Tri-Flow, for the fuel caps, and the fuel selector for that matter.

[OR75]

The Castle nut may need to be adjusted  

[AIREMATT]

[StevenL757]

On 6/22/2022 at 7:04 PM, KSMooniac said:

I'm pretty sure the maintenance manual calls out general purpose oil, not Tri-Flow, for the fuel caps, and the fuel selector for that matter.

Tri-Flow is indeed specified in the manual for fuel caps.

[MMsuper21]

I kept messing with it and the magic was a drop of engine oil on the top.

[KSMooniac]

Tri-Flow is indeed specified in the manual for fuel caps.

You are correct! I thought it was tri-flow on the o-rings and oil on the shaft, but it is tri-flow everywhere. I just looked in my service manual to confirm... It could be my original (OLD) manual had oil listed and that was stuck in my brain.

Oil would be better than nothing, of course, but I'll use the correct stuff from now on.

Sent from my LM-V405 using Tapatalk

[Shadrach]

9 hours ago, KSMooniac said:

You are correct! I thought it was tri-flow on the o-rings and oil on the shaft, but it is tri-flow everywhere. I just looked in my service manual to confirm... It could be my original (OLD) manual had oil listed and that was stuck in my brain.

Oil would be better than nothing, of course, but I'll use the correct stuff from now on.

Sent from my LM-V405 using Tapatalk
 

Nah, I bet it's stuck in your brain from an old DMAX article you read or someone quoted where Don suggests lubing the shafts with dip stick oil every few months.  I honestly don't think it matter much what you use as long as there is some lube present on the mechanism, but clean tri-flow seems like a better solution than used engine oil.

[WaynePierce]

13 hours ago, MMsuper21 said:

I kept messing with it and the magic was a drop of engine oil on the top.

I just did this and it’s as good as it ever was. One small drop from the dipstick. I’ve ordered a small bottle of tri-flow and a set of rings for both sides and will replace when they come in. Thank you everyone!

[RobertGary1]

In my case its the plunger pivot (#7 in the diagram) that is stiff. Only real solution is to drill it out and replace the pin in it. So far I've lived with it stiff. At one point there was a Bonanza guy who repaired them. Even drilled out the body and put a collar in since they eventually egg out.

[AIREMATT]

10 hours ago, RobertGary1 said:

In my case its the plunger pivot (#7 in the diagram) that is stiff. Only real solution is to drill it out and replace the pin in it. So far I've lived with it stiff. At one point there was a Bonanza guy who repaired them. Even drilled out the body and put a collar in since they eventually egg out.

Probably from a Fueler who didn’t understand how it was supposed to close. I had one that I yelled at as he was about to hit the lever to get it to go down because it wouldn’t push down. He stopped just short of hitting it and I explained to him that hitting it would damage it. I showed him how to line it up properly and push the lever down with a pinky finger easily.

I told him if he had to hit it he was doing something wrong.

[Shadrach]

8 hours ago, AIREMATT said:

Probably from a Fueler who didn’t understand how it was supposed to close. I had one that I yelled at as he was about to hit the lever to get it to go down because it wouldn’t push down. He stopped just short of hitting it and I explained to him that hitting it would damage it. I showed him how to line it up properly and push the lever down with a pinky finger easily.

I told him if he had to hit it he was doing something wrong.

I have lost count of how many times fuel personnel have closed my fuel caps incorrectly, I’ve had to pry them open with a screwdriver I tend to towards staying with the plane when it’s being fueled but that’s not always practical.  It’s a curious thing that a human tasked with fueling an airplane could be so dense as to force a cap closed that is clearly misaligned.