Valve Stem Packing

[mhorowit]

Sometime ago, I opened my Imperial fuel cut-off valve and found the valve-stem packing to have desinigrated. I putzed around with O rings and some of that lube that goes on the primer, but they eventually leaked. So I've been looking at the Teflon self-forming packing. Looks like a piece of string. My concern was it would dissolve or otherwise not work well around gasoline.
I took two inches of the stuff and dropped it in a jar of gas for a week, and today took it out. No signs of deterioration. Based on that, I'm going to try her out. Don't know if the packing will stop the seeping, but I'm comfortable it won't fall apart. - Mike

[taylorcraftbc65]

Re: Valve Stem Packing

Mike,
Please, please, PLEEEAAASE tell me where you get that stuff. I had to take the imperial valves out of my bird and replace them with inline ball valves, (the kind that you use for natrual gas lines), because the originals leaked fuel on my floorboards. You should have heard the purists at the airport wail.
Well they may not be "aviation", but when the "aviation" stuff LEAKS and these don't it's not hard to figure out what to use.
I would like to put the originals back in but ONLY if they DON'T LEAK. They were leaking out the stem that the handle is mounted to, and I could not find the special "rope" that was used, so I went to the valves I have now, and no leaks at all.
By the way, the changes that I made to the stock exhaust are great, it doesn't leak, and I won't have to damn near take the motor off the plane to drop the exhaust.

[mhorowit]

Re: Valve Stem Packing

I found it in the plumbing section of the local mom/pop h'ware store here in Falls Church. I would think any store that sells plumbing hardware would have it.
If you have no luck, let me know and I'll mail you 6", which is enuf for 2-3 valves - Mike

[Forrest Barber]

Re: Valve Stem Packing

Waxed rib stitch cord works too. The stem packing does not do anything except while valve in motion for a moment. The valve needs to be "seated" so there is no leak to begin with. Usually they need to be squared off, shortened a wee bit and trued up to fit the taper correctly. Then use "fuel lube" as a lubricant. Tighten the packing nut and away you go . there is only head pressure on the valve.

[taylorcraftbc65]

Re: Valve Stem Packing

Thanks for the offer Mike, I'll go to the H'ware store Monday and see it I can get some.
Thanks for the advice Forrest. I'll give it a shot, and if the valve doesn't leak, I'll stick it back in the plane. I just made a brand new set of oak plywood floorboards with 2 coats of spar varnish when the valve leaked on them. I had to take the boards out, sand them down to the bare wood, revarnish, and reinstall. To say that I was a little "hot" is an understatement.

[alwaysoar]

Re: Valve Stem Packing

Sabrina,
What changes did you make to the stock exhaust? I'm mostly curious at this point since I have a new one installed, but for future reference. Did you cut it in half, or what?

Ed@BTV VT
TF 527

[taylorcraftbc65]

Re: Valve Stem Packing

Allwaysoar,
I cut it in half at the midpoint of the crossover on my metal cutting bandsaw. Then I took 1/4" off the right half, and welded a standard stepdown that I picked up at the local Pep Boys to the right half. Now if I should need to pull one cylinder off, I simply remove that side of the exhaust system.
If you want to see photos, send me a msg at [email protected] and I'll E-mail them to you. Sabrina

[mhorowit]

Re: Valve Stem Packing

Wish there were an easy to test this packing before I put it back in the a/c. I'm using auto gas, so even the smallest seep smells up the place. - Mike

[Howard Wilson]

Re: Valve Stem Packing

Mike, How 'bout a length of plastic tubing with a friction fit over the in port of the valve, slap a hose clamp on it and hang it up for a few days? If you really want rocket science stick a schrader valve from an old innertube with a piece of the tubing clamped around the free end of the hose and put the bicycle pump to it!!! Good to 30,000 ft. ;-o howard

[Forrest Barber]

Re: Valve Stem Packing

Use a piece of vinyl like suggested use about three ft of head pressure to a funnel fill her up and test away..... 19" is the correct height ( head pressure) for the Stromberg carb too....it ain't rocket science...

[mhorowit]

Re: Valve Stem Packing

You mean I don't need either the sliderule or calipers ?
Thanks for the suggestion; I'll do that this afternoon. - Mike

[Forrest Barber]

Re: Valve Stem Packing

Of all the people I met this year, you are the most remembered. I do know that I can kid around a bit and it is taken well. Happy Holidays my friend test away to your hearts content. Truing the valve up is the most important so the taper matches real well, lapping it in works sometimes and turning the valve in a drill press or lathe has to be done some other times.

[Len Petterson]

Re: Valve Stem Packing

Lapping a valve used for gasoline would require use of a very fine lapping compond.
Brass also retains some lapping compounds, the compound stays in the metal.
This couses ware durning it's use.
Using lapping compond for lapping engine valves may be to corse. There is bearing compund, made from pumise for brass what should work well.
Check with you local bearing supplier.
Lapping is an art, so practice make perfect.
Use blueing to check for contact areas. Let it sitt on the bench with just a littel fluid/ gasoline in it.
If it leaks you will know.
I use to test hydrualic valves with methylhydrate it will run trougth anywhere it can.
Teflon is exelent for a sealing material. I have yet to see any fluid what affect it. Liquid teflon, as in pipesealant works for gasoline but let it harden up a littel.It can be difficult to remove the parts as it hold VERY Good.
Be aware of tank conections as you can't but to much tourqe on the thin metals on the tanks.
Just be aware of what the teflontape for pipetread is not mechanicly strong enugh to be used as it will most likely be shewed up opening and closing the valve.
Good old cotton string have used for valve packings over the years.

Merry Cristmas and Happy lapping and flying in the new year.
Len Petterson
Ps I belive in ball valves I seen them holding fluids other valves would not and if you look in new aircrafts ball valves are as selectors of many functions.
As in anything: Know the use, and select the material acordingly!
I know they were not avelable in 47.

[Forrest Barber]

Re: Valve Stem Packing

I was thinking of tooth paste! sorry you are completely correct, ball is the way to go. If C.G. were alive today he would use all the new stuff , he believed in keeping it light`and simple... a lot of automotive stuff was used back then because it was less expensive....

[selje]

Re: Valve Stem Packing

The Imperial fuel valve -- What is the size threads - 3/8 or 1/4 ?
Is the inflow end male or female?
Is the outflow end male or female?