PT20J

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.

No, I know the IA who cared for it, the owner never touched it, that’s what had me wondering if for some silly reason Mooney wrote it to be kept loose, just thought I’d ask before I tightened it. It was a joke

Don't know about Dynon. For Garmin, there are connection diagrams in the installation manuals and my installer marked up the appropriate documents showing what was connected to what. There are also configuration documents that needed to be filled out to show how the units were configured since there are a LOT of settings that are set up in config mode. I took the Mooney schematic pdf to a print shop and had a D size copy made and the installer marked up any changes to the Mooney wiring.

Hmmm. The number of individuals interested in purchasing a gear set seems to have dwindled substantially from the original 100+

Well, you are probably the only one that read the document and everything you say is contained therein. My point is that GAMI did fuel system materials compatibility testing and the FAA evidently approved it. So, the swelling is likely in the expected and acceptable range and may be slightly beneficial which is what George has said. My point is that just because there is some swelling does not necessarily mean that there is a problem in service. George made the comment the Viton is a better material which is also true, but some have extrapolated this to mean that G100UL will require replacing all the o-rings in the fuel system which no one (GAMI or FAA) has said. I'm not defending GAMI or the FAA, but I think we need to understand the facts. I would like to see testing done to industry standard specifications and the results published. Keeping the nature and extent of testing under wraps creates suspicion (maybe well founded if the results are suspect). Frankly, I'm more worried about the paint. George said somewhere in one of these threads that he soaked (ten I think) panels from customer's Bonanzas for a week or so with no ill effects. That doesn't sound like a very scientific or controlled test. And, perhaps Beech used better primer or did a better paint job than Mooney. The original 1994 paint on my M20J is flaking off on the leading edges and a lot of flat rivet heads that are not loose. I talked to Brandon and Sunquest where I am planning to paint my plane this spring and he said he has seen a lot of that on Mooneys. My 1978 J was only 15 years old when I sold it and the original paint was very thin and starting to wear through. So, I think the testing should have involved a lot of different components from different airplanes and different vintages in varying condition.

I always thought that Dukes made the original 20:1 gears and Mooney designed the 40:1 retrofit gear set. Does anyone know for certain if this is the case?

According to Parker, some o-ring swelling is acceptable when the o-rings are exposed to fluids. The bigger problem is if the exposure causes shrinkage. ORD-5700.pdf

Bendix changed all the diapgragms in the servo and flow dividers to flourosilicone in 1980. https://precisionairmotive.com/wp-content/uploads/2019/06/RS-76-Rev1.pdf

https://www.autofuelstc.com/

I can't really make out your picture. It kind of looks like the seal is on the wrong side of the flange. But regardless, the general idea is that air is supposed to flow through the oil cooler, not around it.

Some previous owner probably read on some internet forum that the alternator should be loose.

How much slower is "significantly"? I have electric speed brakes and the left is maybe a second slower than the right (I haven't timed it). It doesn't make any noticeable difference in the way the airplane flies.

I mostly fuel with self serve. I very occasionally overfill and I never wipe the 100LL off -- I just let it evaporate -- and I have never had any staining or deterioration on the white wing paint. Catalyzed polyurethane paint is pretty tough. I have used MEK on it to remove some paint splatters that got on it when it was in another shop and it only slightly dulled the paint where I rubbed hard. But, it polished out completely with Turtlewax polishing compound (which is less abrasive than rubbing compound). The G100UL must be pretty aggressive if it permanently stains polyurethane and will not rub out.