Fuel valve rebuild and manual mistake WARNING

[n2582d]

Bruce,
That's it--CessnaParts.com has the superceded p/n for the shaft o-ring as M83248/1-010. Thanks again.

[mbram]

Just for reference the MS29513 is a dynamic oring the MS29512 is
a static oring(use with unions etc. )

I have the older forged style valve used on the 170A.
the original packing #0413020-4 crosses to a 38481 at
cessna parts. The 120-140 associattion has a cross reference listed
as ms29513-011 (.18 at Spruce).

Do not use parker fuel lube on internal parts. fuel lube is impervious to
fuel and will clog the main fuel screen. Use petroleum jelly or Parker o ring
lube for build up of internal o rings and parts. Use Parker fuel lube on
threads and gaskets.

[mbram]

Another source for fuel selector seals. McFarlane has a kit with upgraded o rings



http://www.mcfarlane-aviation.com/Produ ... r=FSS-KT-2&



Part Number: FSS-KT-2
Description: FUEL SELECTOR VALVE O-RING & G
FAA-PMA
PMA Supplement R22
Qty per Aircraft:
Unit of Measure: EACH
List Price: $31.37
Inventory Status: Stock
Your Discount Price: $25.10
Qty

Please verify eligibility for your aircraft
Product Image

Kit Contains:
1 MCM83248/1-010 O-RING
2 MCM83248/1-012 O-RING
1 MCM83248/1-111 O-RING
2 MCM83248/1-116 O-RING
1 0513125 Selector Valve Gasket

[n2582d]

My o-rings were rock hard. It took some work to remove the inner o-rings (#16).*** In the process I damaged a retainer (#17) pictured below. Next time I'll gently cut the o-ring with a sharp x-acto knife. What would you pay for that little retainer? I figured it couldn't cost more than a couple of dollars. Wrong. $68 each!

*** Moderators note: Again let me remind folks...the ORING is NEXT TO THE LARGE BALL...and the retainer is toward the center of the valve body. In other words, the retainer remains in the valve body and is NOT REMOVED ordinarily. It merely provides the oring a place to reside and prevents it from falling-in towards the center of the valve body. Be VERY CAREFUL using a pick to remove the oring and let the retainer stay in place.
AGAIN... in the IPC illustrations the ORING is actually item 17 and the retainer is 16. The IPC has MIS-labelled them. !!!!

[N2625U]

What would you pay for that little retainer? I figured it couldn't cost more than a couple of dollars. Wrong. $68 each!

P9150627.JPG

Fuelvalve.jpg

HOLY $%@# (insert expletive of choice), guess I should be used to the price of some Cessna parts by now.

[blueldr]

Are all of you guys that are tearing into these fuel selector valves certified Aand P technitions, or is this just some more bootleg owner stuff?

[GAHorn]

Are all of you guys that are tearing into these fuel selector valves certified Aand P technitions, or is this just some more bootleg owner stuff?

All the work described here is under the direct supervision of the scores of certfied technicians that read these forums.

[n2582d]

Are all of you guys that are tearing into these fuel selector valves certified Aand P technitions, or is this just some more bootleg owner stuff?

In my case a combination of the two. I only wish the certificates in my wallet offered immunity from making stupid mistakes.

To help the next guy avoid some of the pitfalls I had ran into rebuilding this valve I'd like to post some picture and offer some advice.

1. RETAINERS In an earlier post I shared about the cost of those little retainer rings. If you can avoid nicking them when you remove the o-ring on top of them you'll save yourself a lot of grief. A writer wrote into Cessna Pilot's Association to say that, "Removing O-ring (no. 16) requires a pick, and there is a high risk of damaging the retainer and/or distorting the new O-ring when you insert it. I discovered this after buying all new internal parts, and then my AI got a confession from Cessna that 'no, the retainer cannot be removed.' Even they have been unsuccessful in trying to overhaul the valve when the retainer and/or O-ring (No. 16) must be replaced. They found that is (sic) usually leaks after being repaired." My concern was getting the new (expensive) retainers in without damaging them. They are quite fragile being made out of aluminum. The inner lip especially is easily damaged. I found there is an interference fit of .004" between the valve block and the retainer O.D.--it doesn't just slide in. I chamfered the bottom outer edge of the retainers and lubricated the retainer and housing. Then I carefully tapped the retainer in using the cap to a BiC brite liner highlighting marking pen. It fits perfectly in the groove for the o-ring.

BiC brite liner retainer driver

2. O-RINGS I replaced the o-rings with like-sized ones made from Viton. They'll last longer and are more resistant to chemicals such as ethanol.

Exploded view

Retainer and o-ring in place

3. TESTING The last thing I want to do after getting this installed is to have to take it out again if it leaks so I improvised a way to test whether the valve leaks. The valve sits about 54" below the top of the fuel tank. I figured this comes to a bit less than 2 psi of pressure. (I'd appreciate if the engineers out there could confirm this.) Using a brake bleeder and a fuel pressure gauge I was able to confirm that the valve wasn't blowing bubbles at 2 psi.

The bucket doesn't hold water ...

but the valve holds air pressure--no bubbles!

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.

[cessna170bdriver]

...The valve sits about 54" below the top of the fuel tank. I figured this comes to a bit less than 2 psi of pressure. (I'd appreciate if the engineers out there could confirm this.) Using a brake bleeder and a fuel pressure gauge I was able to confirm that the valve wasn't blowing bubbles at 2 psi...

Gary,

Using a 54" head and 6lb/gal, I get 1.4 psi. Looks like you're good to go.

Miles

[n2582d]

Thanks for checking Miles. I pressure tested both fuel inlet ports with the valve in the off position. But now I realize I need to also check for leaks around the selector shaft with the outlet port capped and the valve open. This would also insure that there are no leaks around packings #13 & #19 or the cork gasket #10. I think I'll reduce the pressure to 1.4 PSI to improve the chance of no leaks.

[cessna170bdriver]

It just occurred to me, shouldn't you also account for g-loads? (I'd guess 4.4 for the utility category for worst case.)

Miles

[n2582d]

Yes, I probably should account for the 4.4 g load. So 6.16 psi then? Wouldn't a greater pressure push the check ball (#18) tighter against the o-ring (#16)? I wonder if that o-ring would be more likely to leak at 1.4 psi than 6.16 psi? Really the only time those two o-rings (#16) need to be sealing is when the engine is not running or balancing fuel using one fuel tank. Not too often I'll be pulling 4.4 g's deadstick or for an extending period on one tank. I would think the other seals--especially the shaft seal--are the ones that are likely to leak at 6 psi. We'll see when I get home next week.

[cessna170bdriver]

I really don't know the answer; hopefully George can quote us chapter and verse as to what the valve should be tested to, but I'd think it should be tested over the full range (not just the maximum) of what it would see in service, plus some. Also, I'd think a definitive test would be with fuel, not air. Many times the media makes a difference.

As for the likelihood of ever needing the valve to not leak at 4.4g's, you're right that it is out on the edge of probability, but I'd hate to have an engine fire, get it out by shutting off the fuel, then having it re-ignite because of turbulence or the necessity of a tight turn to make a safe landing area.

All that said, the one time I overhauled my valve, I was happy to not have it leak on the ground. (I don't recall the particular cause, but before overhaul, the valve would feed from both tanks regardless of position. I discovered the problem one day, when more than an hour into a flight I noticed the valve in the OFF position ).

Miles

[n2582d]

Dave at McFarlane Aviation was very helpful in resolving this question. He said the specs call for 5 psi but they test them to 6 psi. I'll try filling the lines with fuel before I pressurize them.

McFarlane can overhaul the valve for $475 if you give them a good core. I'm feeling much better already about the frustration and expensive retainers I damaged and had to replace. Shouldn't I get about $400 credit with my wife on the 170 rebuild account?

[Bruce Fenstermacher]

Gary,

I've been reading your saga and to be honest, shaking my head just a bit. You see I removed my valve, opened it up and installed the new o-rings in a few minutes. Put it all back together without testing and reinstalled the valve back into the aircraft in about 2 hours. I'd expected it to take longer and afterward thought, hey no big deal. It's worked perfectly since.

But believe me I've been were you are as well. Open up what seems to be a simple widget to find you've just screwed something up and it will never be the same. You know how it goes. Take out a screw and the whole mouse trap explodes with springs flying and tiny ball bearings rolling everywhere.

I'm starting to think reading your posts, boy was I lucky with that valve. How'd I manage that.