Getting 108-3 N6635M back into the air
Im going to add your photos to my page of Fuel selector info.
Bruce, looks like your valve has been neglected for a long time. Obvious fuel seepage. You found out why the valve is a pain in the a** to work on. When mine started leaking quite a few years ago, I replaced it with the Univair valve, which doesn't require periodic maintenance. I'm not sure I'd recommend that, though. The new valve, although it's sized for 1/2" tubes from the respective tanks, internally has 3/8" passages which restrict the installed engines in the airframe to no more than the 165hp installed. In the future if someone wanted to install a bigger engine they would have to re-install an original valve. The Univair valve works beautifully though; very smooth with positive detents and no leaks. When you get yours back together use a little Marvel (MMO) in your fuel, which I think helps to keep it working smoothly. Mine was still working great when it started leaking. I wish I had just replaced the packing.
Thanks, Dennis, I have been considering these options: (A)removing the valve and replacing it with a new one; (B) overhauling it after removing it; or (C) overhauling it "in situ".
I have decided to do option C because:
Option A has the disadvantages you point out: decreased fuel flow and no engine upgrade option. Plus it costs a lot of money.
Option B would be my most preferred choice. I would love to get the whole unit in my hand for close inspection and cleaning/refurbishing. But the risk of twisting the soft aluminium fuel lines is too scary to me.
Therefore I have opted to do it in situ. Option C.
I will do my best to disassemble and clean and lube this valve in place. That will allow me to do what I can to make this selector work and yes, I may need to do it again in a few years but I will know what to do. Thank you for the MMO tip. I have used it before and I swear it's really magic.
With respect, I disagree with using Marvel Mystery Oil for anything on an aircraft. If you want to lube a fuel valve, use fuel lube. This ain't a tractor.
Carl, thank you. I will do this. I believe my back will thank you tomorrow!
Thank you for the respect you give. I’m pleased to reciprocate. So to put any question to rest, I am using Fuel Lube in my fuel valve. The Marvel Mystery Oil suggestion Dennis gave was about using it as a fuel additive, not specifically on the selector.
In any case, I would ask you why not use off the shelf, non-aviation-specific products on your aircraft if they simply do as good a job as the aviation specific products?
Saying an airplane “ain’t a tractor” seems to me to be a bit disparaging to the mechanics and farmers who keep their tractors and other machinery (including airplanes) operating through all sorts of challenges.
Clearly there are situations where you should use aviation specific tools, materials and consumables on an aircraft. But it seems a bit chauvinistic to imply that one should not use non-aviation products/materials/etc. on an aircraft. I think there is room for discussion with that issue.
@clemensfam3sbcglobal-net Bruce, to Michael's point, MMO is not an FAA approved additive, but I think it's been around since WWII or sometime thereafter and has been used in aviation applications as well as other engines. I started using it because I believe it might help with top cylinder lubrication, but I have nothing to back that up, although I haven't had any issues with sticking valves. I think lubricating the fuel valve just happens to be a side benefit of using the stuff. Mine was always smooth.
What Kind Of Fuel Am I? *
*Sung to the tune of the song “What kind of fool am I?”
That song has been in my head most of the day, ever since this morning when I unleashed a small torrent of gas into the cabin of Sammy.
It all started with yet another spritz of PB Blaster. Here’s what happened.
I had removed the cover (AKA “Bonnet”) of the fuel selector. The selector valve was still stuck in the housing. Nothing was leaking. I was ready to try to loosen the valve assembly when Jim, my ex-bush pilot friend shows up and asks what I am doing. I explain that I am ready to try to free the valve assembly and could use another pair of eyes on what I’m doing. Jim readily accepts.
So as he leans into the cabin through the right hand door and looks up at the selector housing at the firewall, I lean in to the left hand door and snap a small vice grip onto the shaft. I jiggle the vice grip and sure enough, the valve begins to move. I twist the vice grip and sure enough it begins to turn. Then all heck broke loose.
Please allow me to digress a moment. All the instructions I have found that tell how to work on this selector “in situ” say to drain all the fuel through the fuel sump at the bottom of the fuel system in front of the firewall. Well that’s great if you have a fuel selector that allows you to do that. Why do I need to overhaul the fuel selector? Because the fuel selector is stuck! Even though the tanks have nothing coming out of the drain cocks, there is still a lot of fuel in the lines leading from the tanks and there is no way to drain them if the fuel selector is stuck on “off” or on one of the tanks. But I didn’t think of that until all heck broke loose.
So after I jiggle and twist the shaft gas starts spraying out the front of the selector housing and I send Jim to the workbench for a roll of towels while I try to staunch the flow. I manage to push the valve assembly back into the housing enough to slow it down to a dribble, and as Jim started mopping up the worst of the spillage I scramble for a fire extinguisher (always kept handy) and a container to put below the selector housing to try to contain the gas.
We finally used a funnel with a hose to drain into a 5 gallon bucket and collected most of the gas before the gusher finally petered out.
Oh and the flow of gas managed to dissolve enough of the varnish on the valve assembly that it popped out in the rush and landed in the funnel.
Getting things dried up and secure, with lots of kitty litter on the floor,I have a bucket of more than a gallon of fuel in addition to maybe a quart lost down the bottom of the fuselage in the first moments of the gusher. But the wood floorboard of the cabin is nice and clean. A nice breeze through the hangar in our good dry New Mexico air dried everything up quickly.
What follows are pics of the situation and the work done tonight on the valve assembly.
Varnish and gunk all over. No wonder this was seized. I soaked it in kerosene and wire brushed everything.
I chucked the valve in my drill and worked it over with 400 then 600 grit.Used my gun cleaning kit to get the gunk inside the holes.
All in all it turned out pretty nice.
Tomorrow or the next day I will tackle the housing that is still in situ.
Whoops!! Looking good, Bruce. You can see that the 'packing' is a far cry from an "O" ring which is what people advise using when your packing starts leaking. Hopefully yours is still intact enough to re-use. I wonder if a little fuel lube on the packing might help preserve it some and keep it from leaking? The cone looks spiffy now and should work well.
Bruce, when you get the valve re-installed, assuming both tanks are empty, you might want to pour a few gallons of gas into each tank, first one side and testing and draining that tank completely; then the other side, and make sure when each tank is selected, that fuel drains through the gascolator from the selected tank. It would be easy to get the cone in the housing in the wrong orientation.
I plan to use the multiple O-ring method and not try to reuse the cork gland. Although with fresh cork one could probably duplicate the originals' form and function. I am not that much of a purist.
Tonight I just removed the fuel selector handle and tube and tomorrow I plan to sandblast, prime and paint them. I am waiting for rubber grommets to be delivered. There was a rubber grommet in the instrument panel where the fuel selector shaft goes through. Can you buy a rubber grommet at an auto supply? There are like four auto supplies up in Deming, a half hour away...Or maybe True Value. There's one of those too. No big box stores here. Nearest are Las Cruces or El Paso. Long way to go for a grommet.
Anyway I have an idea. (as my wife likes to say at this point, "oh oh...")
Chuck the valve cone in my electric drill, apply a bit of valve grinding compound, place it in the in situ valve body and slowly grind away.
It should mate the two surfaces well. And then flush liberally with fuel, drain and clean the valves, lines and sump, etc.
I think that would be the easiest way to overhaul the valve body when it is not removed from the airplane.
Hi Bruce, I recently ordered grommets from rubberfeetwarehouse.com. Easy to find the right size and I got mine in 4 business days for $3.82 shipping.
Also recommend going easy with the lapping. You might want to consider doing it by hand. The metal is a bit soft and laps easily.
When I rebuilt my airplane 17 years ago I replaced the fuel lines. Since then, every few years during the annual, I remove the fuel valve as it is fairly easy to remove without damaging the lines if you take it out often enough. I have a spare already refurbished valve to install so I can refurbish the old one at my convenience. If you damage a line removing the valve, you could always cut the line past the curved part where the line straightens out and splice in a new curved part using AN or MS hardware. While at it, you could also replace the fittings on the valve from "automotive type" compression fittings to aircraft AN or MS type flared fittings, making subsequent removals a piece of cake. FAA guidelines on vintage aircraft allows the use of modern aircraft components/hardware if form/fit/function remains the same. It is not considered a major repair.
Of course when I do my valves I am on a workbench and it makes it a lot easier to clean and lube everything prior to installation. I set up the valve body in a machinist vise and put the cone in a drill press. I use good old plain Colgate toothpaste to lap in the cone as it is about as mild an abrasive as you can use and it rinses off easily. I would stay away from valve grind compound, it is designed for steel-on-steel grinding, not brass. As stated in an earlier post go real easy on the fuel lube but don't go without it.
As for earlier comments about Stinsons not being a tractor, that is true, but almost all these old vintage airplanes (Cubs, T-crafts, Luscombes, Aeroncas, etc,etc,etc, used a lot of off the shelf automotive and tractor parts and hardware. They didn't re-invent the wheel when they needed something like a gas cap or a starter solenoid or a hose fitting, that's how they bade thousands of these post-war airplanes affordable. I believe Maule still uses parts that are available at Tractor Supply and NAPA.
One last item to cover is MMO. I have used MMO and mogas in my Stinson for over 30 years and I never had a fuel problem and I think it does help with the fuel valve. I also use it as an upper cylinder lubricant in all my air-cooled engines including my 4 wheelers, lawn mower, snow blower, and my 1962 Chevrolet Corvair Pick-Up. I also think that lubricating qualities of MMO sloshing around aluminum and steel fuel tanks and lines help in preventing rust and corrosion.
Bob PicardN6346M Stinson 108-3 Floats/Skis/Wheels
N48923 Taylorcraft L-2B skis/WheelsAnchor Point, Alaska
Hi, Bob, thank you for that thoughtful post. Along the lines of folks using off the shelf parts in the olden days, I can't help but think of the Pietenpol, specifically designed to be built by the "common man" in his garage using readily available parts and a farmer's skill set.
Today was a light day. I am still considering the best approach to clean and lightly hone the inside of the valve body in place under the instrument panel. I am still leaning toward using the valve cone itself as a tool to very lightly lap the cone and body together. Then removing and cleaning the cone and flushing everything out of the body.
I spent most of my time today on the fuel valve rod and selector knob. Sandblasted, primed and painted them.
I also removed the gascolator to clean it.
I will leave it off as I need to clean the fuel lines once the valve is reinstalled. I will flush the valve body and lines out with the fuel I collected when I first removed the valve and let that dirty fuel drop into a bucket.