Fuel valve rebuild and manual mistake WARNING

[n2582d]

Bruce,
McFarlane is giving me a cut of the action on all the business I'm bringing them . Seriously, I'm shaking (and scratching) my head a lot too. This valve is really a pretty simple device. My problem is the "might as well" syndrome. Take a look at my posts on the trim actuator for another good example of this. I figure I've gone this far, so I might as well do this one extra step. In the case of this valve it's replacing the retainers (which I never imagined were that expensive), installing the best o-rings I could find, pressure testing it (putting ones lips to the inlet fitting and blowing would adequately prove whether it leaks or not), or modifying the mounting of the valve with nutplates. I've come to terms with the fact that I'll never fly the plane at this rate but I enjoy process of this rebuild (and look at the money I'm saving on insurance, gas, cases of oil , hangar rent, and database subscriptions) ! After a week of flying nights in lousy weather it's therapeutic to come home and tinker on the plane in the shop.

This plane has seen a lot of neglect and abuse in the last 50+ years. It has been in two accidents where the pilot lost control after the seat slid back. After I bought this plane the FAA pulled the certificate of the A&P/I.A. that had previously "maintained" it. As I tear into the wing I'm finding a number of undocumented shoddy repairs. I'm sure the plane has and would fly fine if I left them that way. The casual observer would never notice these repairs. But instead I'm spending a lot of time and money replacing or fabricating wing parts and building a wing jig. It would be a lot easier to just find another wing in a salvage yard but I enjoy the challenge of rebuilding it. I've built composite wings, rebuilt fabric wings, but never rebuilt a metal wing. Someone is going to get a nice plane with a lot of minor alterations when I lose my medical.

[Bruce Fenstermacher]

Good for you Gary. What your doing is just one part of this hobbie lots of folks never get to enjoy ...and many don't want to.

When you mentioned McFarlane I had a very quickly passing thought that if I pulled my valve again and replaced the o-rings I could feel good about saving another $400. If I did it say three or four more times I'd have saved enough to go out and buy some widget I don't need for my plane.

[n2582d]

When you mentioned McFarlane I had a very quickly passing thought that if I pulled my valve again and replaced the o-rings I could feel good about saving another $400. If I did it say three or four more times I'd have saved enough to go out and buy some widget I don't need for my plane.

Now you're thinking like me Bruce!!! When (or more realistically, if) I ever get done with this project I will have the aerial version of the cars on Pimp My Ride!

Click here for a way to spend all the money you'll save re-rebuilding you fuel valve. Just think--a polished plane without the polishing! Now quit salivating all over that keyboard, you're going to short it out. Bruce, we could get our planes out of the Rat Class with this. Heck, we could be competing with the likes of Jacobsen, Wood, and even Horn!

Chrome paint

[170C]

If you guys start putting that chrome paint on your airplanes you are going to have to furnish dark sunglasses to all of us gawkers

[DaveF]

4. MOUNTING The cabin floor skin is out in my plane so I plan on adding two one-legged nutplates to the valve mounting bracket. That should make it a lot easier for the next A&P mechanic or "bootleg owner" working on the valve.

Or flush rivet them to a floating piece of aluminum, like this.

[Bruce Fenstermacher]

Heck, we could be competing with the likes of Jacobsen, Wood, and even Horn!

Jacobsen and Wood maybe but Horn is in a class by himself.

Dave I like the idea of the nut plates on a floating piece of aluminum. I'll have to file that idea for future use. Just hope I remember it when I can use it.

[170C]

Our B model (and 172) fuel valves look different from the one shown, but they could also have nut plates installed in some manner (I think?). Wish I had of done that one of the two times I have had mine out. The most difficult part of the entire process of removing & reinstalling the valve is getting at the nuts that hold the valve in place. You can sure tell that the engineers never gave any thought to the valve having to be removed Lots of grief & scratched/bruised hands & lower arms (x%*@!#^*)

[n3833v]

I agree, all engineers need to work on the line after they design something to see how difficult or easy it is. I know in my work the engineers bolted 2 units together and installed on the engine. When we needed to remove the one unit, I had to design a special wrench to get them apart and then reconfigure the installation. Many times a person needs to make changes and never gets credit for an improved product.

John

[bev5887]

I have read this thread and would appreciate any thoughts. What could be the potential effect, in flight, of a misassembled fuel selector valve? What would happen if two washers were installed on the cam shaft below the o-ring that seals up against the valve cover when the valve is assembled? What happens if the o-ring is loose within the valve body due to mis-assembly? Thanks

[blueldr]

Perhaps it would be wise to specify whether or not this rebuild of the fuel selector valve is owner/pilot or licensed mechanic type maintenance. It might keep someone out of trouble with the fuzz if it is entered in the log book.

[bev5887]

Repair was done by owner/licensed mechanic - discovery of error by NTSB. Just trying to understand if misassembly would influence operation.

[Bruce Fenstermacher]

This repair/rebuild would not fall under owner operator maintenance as allowed by 43.13 appendix A. However it is something that could be accomplished by most owners, who know which end of a screw driver to hold, while under the supervision of a licensed mechanic. The hardest part of this is the contortions required to get your hands inside the tunnel with the proper tools to do the job.

My bet is that an improperly assembled valve will not seal. That is what will happen if it is assembled in the order as depicted in the IPC. A smart person would do a crude test by pressurizing each side with a pound or two of air (blow into it like your blowing up a balloon) and check operation before reinstalling the valve.

If a test is not performed and the valve won't seal you won't be able to shut off your fuel which means your probably no better or worse off than before you started the maintenance. If you somehow cut the o-rings leaving debris in the valve it will be caught by the gascolator and your in no more danger than having old o-rings deteriorate, crack and crumble inside the valve. I would thing the same is true if somehow you left an o-ring loose in the valve. Basically a loose o-ring or debris would block the ball from sealing against the ball and fuel would continue to flow. If you somehow blocked fuel flow with the rebuild it is unlikely your engine will start because your fuel system has to be drained to accomplish this maintenance.

Certainly after the valve is reinstalled, as part of an operational test, one would check for fuel flow in the BOTH, LEFT, and RIGHT positions as well as no fuel flow on the OFF position before any attempt at flight.

[cessna170bdriver]

Ever since I first had to do maintenance on my fuel valve, I've had this picture in my mind of the very beginning of the Cessna 170 assembly line being a fuel valve hanging by a thread from the ceiling, then the airplane being build around it.

Miles

[Bruce Fenstermacher]

As for your question of two washers on the cam shaft (#8) under the o-ring. I do not recall what the tolerance is of the cam shaft from the bottom of the valve to the top plate. This tolerance would also change depending on the thickness of the gasket (#10). If a thick gasket was used two washers might be required to get o-ring to seal at the top of the shaft.

What would be the effect of two washers if used? Well first I'd think that if two were used it means that using one wouldn't seal and I'd have to find the reason why. Second once satisfied why two washers were required and having inserted two washers the valve would either work properly meaning the cam would turn and the shaft wouldn't leak or the cam would be to tight and not turn and the valve would not function being stuck in what ever position it was assembled. I'd think this malfunction would be pretty obvious before one got to far.

I won't comment on whether it would be proper to install two washers in this position other than to say if the cam turns and doesn't leak there would probably be no further consequence. I'd probably exhaust all attempts at getting a thinner gasket for the top plate before installing two washers however.

[Bruce Fenstermacher]

Repair was done by owner/licensed mechanic - discovery of error by NTSB. Just trying to understand if misassembly would influence operation.

bev5887 could you please elaborate what you mean by "- discovery of error by NTSB."