Fuel selector problem

cfiatzph · Post by **cfiatzph** » Mon Feb 05, 2007 11:29 pm

Ok, not a C170 but the SAME fuel selector. (1956 c-172) After a engine overhaul and a total fuel system overhaul (including fuel selector) the a/c sat for a while. Upon putting fuel in the tanks the fuel selector wld not shut of fuel properly. So...I pulled the fuel selector and replaced with the proper o-rings. The right side nipple or intake into the fuel selector keeps leaking into the belly. Twice I have taken the fuel selector out and replaced the o-ring on the fitting/nipple each time it leaks. I know it is the right side (and not the fuel line) because if I drain fuel out of the right tank and put a AN cap on the right side of the fuel selector and fill the left tank and put it on both it does not leak. What is going on? Any advice? I am not sure if the block is too far gone or what? Anybody ever seen this?

Post by **GAHorn** » Tue Feb 06, 2007 1:49 am

Are you talking about a leak at PN 0513120-3? Or are you talking about the AN fitting that screw onto that nipple? Or are you talking about the O-ring beneath that nipple? Or are you talking about the body that nipple screws into?
If you mean the AN fitting you probably have a damage flare or need a "Del" seal. Otherwise you may need a close look at the nipple itself and/or the body to detect scratches, cracks, damage, etc.
Permatex may also seal up imperfections but I'm leary of using it in this area due to the inconvenience of later repairs should it fail again.

Post by **Bruce Fenstermacher** » Tue Feb 06, 2007 3:10 am

We talk about this valve from time to time so here is the illustration from the 170B parts manual with one change as noted.

cfiatzph if indeed you are talking about leaking around part #21 then I'd suspect a crack in that part. Or could you have crossed the thread and the nipple is not seating squarely against the o-ring and the main valve body?

cfiatzph · Post by **cfiatzph** » Tue Feb 06, 2007 2:19 pm

Somewhere between #21 and the block it is leaking.
I think I'm gonna try another block and nipple.
Thanks

Post by **Bruce Fenstermacher** » Tue Feb 06, 2007 4:49 pm

cfiatzph wrote:Somewhere between #21 and the block it is leaking.
I think I'm gonna try another block and nipple.
Thanks

Easier said than done I might think. I doubt the individual parts are still available. Cessna recently introduced a new fuel valve to be retrofitted into our airplanes but the new valve was very expensive.

It's a pretty simple design with not much that can fail. Here is what I'd look for.
1. Is the block cracked?
2. Is the nipple (#21) cracked?
3. Are the threads in the block and on the nipple good so the nipple will seat squarely?
4. Is there a bur or some other damage that either is cutting or otherwise stopping the o-ring from sealing?
5. I know the other side is not leaking but are you sure you are using the right o-rings with a cross section big enough to seal between these parts?

Try swapping the nipples from side to side and see if the leak moves with the nipple.

It's got to be something simple right in front of your eyes which is why you can't see it.

jon s blocker · Post by **jon s blocker** » Tue Feb 06, 2007 9:12 pm

I had the same exact thing happen on mine when we rebuilt our plane. I messed with it for quite a while and could never get it to stop leaking. I took it apart and got all the good parts out of it, then went online and got a used one. 172s used almost the exact same set up, (shaft to the indicator was a little different). Put the two together using the better of the parts and no leak. Problem solved. All the correct parts. $45 for the valve assembly with all the fittings and up through the indicator plate and pointer! Make sure to check the flange or flair at the end of the metal fuel line itself. I have seen several joints leak because that flange was bad and very hard to pick up with just by looking at it. A minute crack there WILL leak. Good luck, Jon

Post by **GAHorn** » Tue Feb 06, 2007 11:07 pm

That's a good point, Jon. Flare fittings harden with use and age, and a hairline crack can leak fuel and might be misleading as to the exact location.

The fuel selector update that Cessna developed was not for the 170 B model, but was for earlier "Weatherhead" (brass) valves to be converted to one similar to the later machined "block" valve. (And that conversion is why it's so expensive.)

cfiatzph · Post by **cfiatzph** » Wed Feb 07, 2007 4:32 pm

It was corrosion in the block where there treads go. I wish there was another way to get these parts resonably being that those blocks go bad/corrode after time. I happened to have another block lying around which I used. Only prob is that I think the o ring seat is bad. From the looks of the diagram it only shows the seat but if I am not mistaking there is the seat and then a retainer to keep it in place?

Thanks

Post by **GAHorn** » Wed Feb 07, 2007 9:51 pm

Corrosion can be caused by water.... or alcohol .... (very corrosive!)... or autogas. Yet another reason, in my book, to avoid mogas. It's not as cheap as it seems when it costs as much as it does to replace fuel selectors, etc.

cfiatzph · Post by **cfiatzph** » Sat Feb 10, 2007 2:11 am

Any ideas on the retainers and o ring seats with the above diagram?

Thanks

Metal Master · Post by **Metal Master** » Sun Feb 11, 2007 5:50 pm

I recently got a copy of the fuel selector valve replacement service kit instructions off of the micro fiche where I used to work as director of maintenance. I wanted to see exactly what Cessna was doing. The new fuel selector valve is in most respects exactly like the valve in the drawing above. Except that it uses a different fitting in place of Item 12. It uses a fitting similar to the one use on the Weatherhead brass valve installed in my 170A However the two can not be exchanged because the new fitting is made for the aluminum type valve. It is not used in later aluminum type valves such as pictured above and the one which is similar, used in the brass valve is Pipe thread.

I ordered a serviceable valve from Faeth aircraft in California. The cost was without exchange $375 two months ago. I retro fitted it to my 170A following the instructions contained in the service kit loosely. I did not use the new style fwd fitting as I can find no practical use for it. It has an additional drain fitting plug called off in the service kit. The bottom of the valve I have already has a drain fitting in it. I had to manufacture a new line from the fire wall to the fuel selector valve and a new line from the left rear door post to the fuel selector valve as the new valve & fittings are about Â½ inch narrower and about 3/8 inch shorter than the original weather head brass valve. The new valve from Cessna is available without the entire service kit for around $1,100. Quotes I got from other aircraft salvage yards were from $470 to $650 out right as removed. Faeth A/C sent me a serviceable valve with new o-rings installed and aluminum tape neatly fitted over the AN fittings to keep out contamination. I dissassenbeled the valve and inspected it anyway. It was as they said. It had all new seals (O-Rings). I installed the valve exactly like the Service kit called out in all other respects. I am curious though as there is one part that is required to connect the fuel selector shaft in the service kit that is not called out in the original parts catalog or the service kit. It is the short stub shaft that inserts into the part labeled #1 in the drawing above. I also had issues with the drive shaft clearance where it comes through the floor. I had to enlarge the hole aft to eliminate interference. The service kit does not address this issue. Whether it would be an issue with the actual service kit is a question only the financially unencumbered can answer.

Now I can change the position of my fuel selector without fear of breaking the universals in the shaft. And the fuel tanks do not cross feed when in the off position which the old weather head valve did.

The service kit instructions include drawings for installation in all serial numbers of Cessna 140, 140A, 170, 170A, & 170B aircraft. Although I think it unlikely that Cessna will sell a lot of these kits at the listed price. Around $5000 for the complete kit I think.

I can send a copy (it is copy written) to the association. It is at least interesting to see.
The drawings are nice. I know that not including all of the part number refrences in this post may be frustratiing but I did not want to spend all day writting this post.

mantry · Post by **mantry** » Wed Oct 17, 2007 12:59 pm

We have a 170A, that for a long time the fuel selector valve is very stiff to operate, so to NOT risk breaking something, we don't turn it much. IE: As you rotate it, there is a Squeek, Squeek as it groans.

I would like to remedy this as I have heard (not substansiated) that these valves are prone to fail and if they do, it is a massive failure with fuel running everywhere.

I looked over this note, and I would say that ours is NOT the machine valve block but a cast one, but that is from looking at it last November during the annual and my memory.

Questions: What is the cost and source to replace this valve? I've heard everything from $45.00 to $1000.00

Is it worth trying to repair the valve?

Any hints at getting this valve in/out?

Again, no problems with the valve other than it seems a little stiff when turning like I'm sure we have all seen in other gas related valves that have been in service for a long time.

We did run MOGAS in it for a while but have not done so for the past 8 years or so.

Thanks again for all your help.

Post by **GAHorn** » Wed Oct 17, 2007 1:16 pm

Fuel shut off valves are critical equipment and should be kept in good operable condition. (How else are you going to fight a fire if you can't get the fuel turned off?)

Parker Fuel Lube will lubricate the interiors of the valves and keep them operational.

You are right not to force the valve if it's giving problems. Forcing it will scratch/score the interior and may render it un-repairable. But if you remove it, clean it, inspect it, ...you can probably rebuild it using new O-rings (cheap) and save it. Otherwise, it will cost you money. Lots and lots of money.

Post by **Bruce Fenstermacher** » Wed Oct 17, 2007 2:03 pm

George is right. Don't turn it you could be ruining it. Take it out and disassemble it. You will see it is a close tolerance fit that actually shuts of the fuel. If there are large gouges in it it will not seal and there is not much that can be done if the gouges can not be polished out.

If you remove it and clean and polish it and reinstall it and it doesn't seal (shut off) your no better off than you are now till you find a replacement.

The replacement from Cessna is extremely expensive. You would be better of finding a used good on or updating to the newer style machine type that relies of o-rings for the seal.

mantry · Post by **mantry** » Wed Oct 17, 2007 11:07 pm

Ok, so humor me....
Price for it new?

Price for it used?

Price for the new style new or used?

The International Cessna 170 Association

Fuel selector problem

Fuel selector problem

leaking fuel selector