PT20J

On my ‘78 J I solved the problem by slightly bending the piece indicated to increase friction on the cam. I may have had to remove the knob to do this. It was 30 years ago and I don’t remember.

@MikeOH we get your point: You want 100LL and G100UL in place simultaneously everywhere you buy fuel until 100LL ceases production and G100UL has been proven to cause no harm. That's not going to happen. There is no infrastructure to support it. And no business person is going to put in a second tank (or truck) at great cost for a situation that will only last a few years. This continued harping on this point is distracting from the very real concerns that have been raised and need to be addressed regarding o-rings, tank sealant, and paint. I understand that GAMI has done years of testing. Some testing may have included third parties; I don't know. The FAA reviewed it all and approved the STCs. But, that was only testing in a limited number of circumstances. The test matrix of all possible combinations in the field is immense. I spent my career in tech product development and I saw many instances where well tested products had unexpected problems when released to the field. Those of us that frequent this forum (or Beechtalk) need only recall Garmin's pains with the GFC 500. If I were GAMI, I would avoid trying to explain everything with "we tested that and found no problem" or "100LL should be worse" and aggressively investigate every report of issues while G100UL distribution is still small and manageable. It doesn't take many issues in this day of the internet to get a population down on a product. Some of those pilot/owners will have their elected representatives on their speed dial. Just my $.02.

But, George’s “replication” was reported to be using 94UL in a Continental IO-550. The UND issues occurred in Lycoming O-360s. https://www.aero-news.net/index.cfm?do=main.textpost&id=39119893-8D1D-43AE-9323-CA08523C6439

UND replaced its entire fleet with new Archers and Seminoles in 2016, so yes.

I believe Lycoming switched to hardened seats sometime in the ‘90s in preparation for future unleaded fuels. It was mentioned when I took the Lycoming factory class but I don’t have any documentation on it. If you want the details, you could call tech support and see if there is a service publication. Lycoming only puts the most commonly requested service literature on its website, so there may be something that you cannot find by searching the site.

Looks to me like an IO-360-A3B6 engine with the bracket for a -A3B6D engine. Probably why there was interference.

Very nice.

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

I looked at the video posted by the A&P at KRHV again. The o-rings he tested were MS28775 and MS29513 which are both nitrile which is listed in Section VII or the Parker O-ring Handbook as having only fair compatibility with 50% aromatic fuels. Also, the test may not be representative of the fuel's effect on the o-rings in service. Specifically on Page 2-7 of the Handbook, it is stated: "When deformed and exposed to a medium, rubber (Note: Parker uses the descriptor "rubber" to refer generically to any o-ring material), when confined in a gland, swells significantly less that in a free state (up to 50%) due to a number of factors including lessened surface area in contact with the medium." I just checked and SAF-AIR fuel drain valves use M83248 o-rings (Viton).

Most of the o-rings in the fuel system are static (for instance the o-rings in the fuel pump fittings and the servo finger screen). The o-rings in the gascolator and fuel valve are dynamic. In my M20J, these components use MS9388 o-rings which are Fluorocarbon (Viton/FKM) which is rated by Parker as satisfactory (highest rating) for fuel containing 50% aromatics according to Section VII of the Parker O-ring Handbook.