PT20J

I suspect that the longevity is highly dependent on the quality of the original application. Personnel changes over the years, factory shutdowns and restarts, etc. might cause gaps in proficiency. The two women that did tank sealing that were interviewed in the Boots on the Ground video admitted that it was a challenging job and had a learning curve and that they weren’t very good at it when they started. Someone got the airplanes they learned on.

Yes

I believe the seats use a hitch pin Rather than a cotter pin.

I’d disconnect the cowl flap linkage to drop the cowl flap down and have a look through the opening to see what’s rubbing on the cowling.

Many shunts are 50 mV at full scale current.

If I understand correctly, the FAA required GAMI to run tests to show G100UL compatibility with fuel system components before it approved the STC. I haven’t seen the ICA, but if there are no airworthiness limitations (which the FAA would have had to approve) requiring changing components to a different material, then there is no requirement to do so. Details of the testing are coming out in dribs and drabs in posts on the forums. Perhaps it would answer a lot of questions we have about the risks to our fuel systems if @George Braly would make the test details and results available as well as any formal approval documentation from the FAA.

There seems to be consensus that up to about 30% volume change is permissible in a static o-ring. The video showed an 8-10% change in diameter. Assuming that the swelling causes an equal dimensional change in all directions, a 30% volume increase would cause a about a 10% circumference increase. The diameter being proportional to the circumference would also increase by 10%. Therefore the swelling appears to be at the upper end of the acceptable range for a static o-ring application and exceeds the acceptable range for a dynamic application. I am not saying (nor have I said previously) that this is acceptable because I do not know whether it causes a problem in service or not.

The OEM F391 and the Curtiss valves do not have replaceable internal o-rings and I don't know what o-rings are used. The external o-ring that seals against the wing skin is nitrile. The SAF-AIR equivalent valves have replaceable Viton o-rings according to the website. It appears that the Gerdes gascolator uses nitrile o-rings. I don't know what material is used in the 600-001-5/8 stat-o-seal. The Airight uses Viton. Airight 51250-9 Gascolator.pdf

Well, to be fair, I believe that George also has a degree in aeronautical engineering and he had some subject matter experts working on the formulation. And, I did not say that the video showing the G100UL soaked o-ring swelling wasn't valid. What I said is that the comparison with the 100LL soaked o-ring may not be meaningful because we don't know the composition of the 100LL sample. Perhaps a different 100LL sample from a different refiner would have also swelled the o-ring soaked in it similarly. No one knows because determining the composition of the 100LL sample wasn't part of the experiment. That's all I was pointing out. We don't really know that o-ring swelling is an operational issue. I'd prefer a test with different o-rings of different materials installed in different configurations simulating actual conditions we see in our airplanes. But, we have another problem that there is no question about with G100UL: It damages paint. Maybe it only permanently discolors paint; maybe it strips it. But there is clearly something going on.

I was treated very well by Flightline First at KNEW a couple of years ago. If you land south at night you will be over the lake which is a huge black hole so I'd recommend the instrument approach.

See, this is the problem when a bunch of amateurs (me included) try to pretend to be materials engineers. Aviation fuels have always been pretty nasty stuff. At some point we have to assume that the engineers and the FAA know something about what they are doing. I looked into hoses a few days ago. It's hard to tell the exact composition because the Mil Specs don't specify the material except generically as "synthetic rubber compounded with the necessary ingredients to meet the requirements of this specification" Interestingly, the hoses used for the short connection between the fuel tank outlets and the aluminum fuel line that goes to the fuel selector are allowed by specification to swell 85% when exposed to "fuel." This hose is designed specifically to be terminated in beaded connections secured with hose clamps. The o-ring swelling comparison in the video may not be meaningful. According to @George Braly (and I have no reason to doubt him on this) 100LL can have varying amounts of aromatics depending on the aviation alkylate used. So, we don't know if the sample had a lot or a little toluene in it. Maybe a different 100LL sample from a different refinery would behave differently. Who knows? And, does it really matter? We get whatever comes out of the FBO's pump. Attached are the files for MIL-DTL-6000D (hose Mooney uses to attach tanks to fuel lines) and MIL-H-8794D (hose material Mooney specified for flexible fuel hoses in the engine compartment). MIL-DTL-6000D.PDF MIL-H-8794D.pdf

References: Weldon pump: M20J IPC Lycoming pump: Lycoming IO-360 IPC Fuel drains: SAF-AIR website (I don't know what OEM parts used and Curtiss doesn't specify the internal o-ring because it is not field replaceable; the Curtiss static o-ring that seals against the wing is nitrile., Fuel valve and gascolator: manufacturer's drawings.

I guess the 100LL should have destroyed my servo by now.

The only nitrile o-rings I could find specified for my fuel system in my 1994 M20J are the o-rings at the input and output boss fittings on the Lycoming and Weldon fuel pumps. Everything else is Viton (sump drains, fuel selector, gascolator) or fluorosilicone (fuel injection). The design of a boss fitting should constrain the o-ring under compression more than other o-ring applications and expose it to less contact with the fuel and I doubt swelling is an issue.

Bendix changed RSA fuel injection rubber components to fluorosilicone in 1976. https://precisionairmotive.com/wp-content/uploads/2019/06/RS-76-Rev1.pdf