The International Cessna^® 170 Association

GAHorn wrote:

GAHorn wrote:.... I’d suggest you replace the cap on that right tank with a serviceable vented cap and consider pulling the drain valve out for inspection. While it’s out...you might want to “flush” the tank to get all the water out.

Hope this helps.

Just to reiterate: I was suggesting only that you replace the cap, the drain valve, and flush out the tank. Although it’s certainly your choice, I would not be eager to change out the filler-neck or it’s assoc’d hardware if close inspection with a mirror doesn’t reveal something obviously unairworthy. (The filler-neck cavity is notorious for holding water after a rain or washing and it’s “threaded” into the tank and will need to be resealed (pro-seal) as it’s reassembled if you get into that. Also, the filler-neck is “clocked” during assembly to align the new fuel cap with the slipstream. Once aligned, it’s staked and sealed... why I’d not be eager to disrupt it.)

10/4. I'll order the cap and drain and go from there, as well as inspect the filler-neck hardware.

How can I upload photos into this thread? I joined the Association last night.

reecewallace wrote:How can I upload photos into this thread? I joined the Association last night.

You can now that I've upgraded your forum privileges. Thanks for joining.

Welcome to the Assoc. and the wonderful world of C-170s! We have a wonderful and knowledgeable group here who love our airplanes and mostly like each other.

Lots of archived knowledge on these forums- the search function has been a friend of mine.

Thanks for joining and again let us know what you need help with. This association is a hugh resource for any owner. Often you can find immediate accurate information on issues you’re facing or trying to resolve. We do like each other as far as I can tell but as you would expect we are all different, some (George) more than others ( ) but we do get along for the most part. I only pointed out that George is different because he labeled me a heretic last week. See we are all normal here.

Reece,
Welcome!
A lot can be done to prevent water intrusion at the filler neck without unthreading the neck. See SIL 170-172-19 and SE 70-28. The screws in the moat originally had cork washers. I’d replace them with Parker 750-0002-10 ThredSeal washers. Instead of using Parker Seal-lub or silicone sealant as these Service Bulletins recommmend I’d suggest something like CS3204.

As others have said, you need to be concerned about the water more than the rust. If the plane’s exposed to the elements you might want to consider an additional drain valve in place of the plug in the bottom of your fuel valve.

n2582d wrote:Reece,
Welcome!
A lot can be done to prevent water intrusion at the filler neck without unthreading the neck. See SIL 170-172-19 and SE 70-28. The screws in the moat originally had cork washers. I’d replace them with Parker 750-0002-10 ThredSeal washers. Instead of using Parker Seal-lub or silicone sealant as these Service Bulletins recommmend I’d suggest something like CS3204.

As others have said, you need to be concerned about the water more than the rust. If the plane’s exposed to the elements you might want to consider an additional drain valve in place of the plug in the bottom of your fuel valve.

Hey Gary, thanks for this.

Yes—my plane is exposed to the elements all the time. I live in one of the wettest climates in Canada and park the aircraft outdoors. I am confident water is pooling then making its way through up through my filler cap and possibly leaking through the 6 screws as well. I've heard mixed comments on this thread saying to replace just the cap and drain, but figure if I have the help of my AME buddy, I may as well replace the screws too.

Do I need to replace the gasket too?

These are the parts & supplies I'm ordering from Aircraft Spruce:
- Cessna vented fuel cap 06-00985
- 6 reservoir screws MS35207-264
- Drain valves stainless steel 05-15418

Parts I still need help with:
- Do I need to order new gasket if I'm putting new screws in?
- The Chemseal B2 09-38500 is out of stock. Can you recommend something else? Do I just coat the screws with this while putting them in?
- Can't find the washers. Can you send me an Aircraft Spruce link to the exact ones?
- Can't find the 8 outboard screws part #PK76XZ-8-10 from the Cessna 170 catalog

I have no intent of removing the filler-neck valve.

As per the additional drain valve, do you mean one on the belly of my aircraft below my fuel selector? I have a drain below my engine I check for water before every flight, but I think this may be called a gascolator?

- Sincerely,

Young & dumb, but curious

This is my bird

Here’s the ipc. See Gary’s post for cross section.
The cork gasket large one is to prevent fretting between the tank cover and the fuel well. The two gaskets: one on the outside of the tank seals the well to the bottom outside of the tank. The second more important gasket; is not depicted nor is the fitting that the filler neck screws into (and staked) is inside the tank. The gasket seals the fitting to the upper tank inside skin and if the gasket is shot then you might have a problem. The screws go through both gaskets so I’m a bit skeptical of large amounts of water getting past the screws. I used parker o lube on the screws when I checked my seals, more to prevent them from rusting in place and making mx down the road more difficult. PRC is overkill but thats my opinion. Parker o lube is like a sticker version of petroleum and repels water and makes taking things apart years later easy.
I’ve got buckets of fasteners, fly over to YPK when we can get together and please take some. Fuel caps and their gaskets I don’t have so you might eye ball those carefully. I think we have had one of the wettest Dec’s on record and so far. this Jan we have had two major storms roll out of the pacific giving us 3.3” in the first 5 days.

Here she is when she liked the cold, ready to go somewhere.

reecewallace wrote:As per the additional drain valve, do you mean one on the belly of my aircraft below my fuel selector? I have a drain below my engine I check for water before every flight, but I think this may be called a gascolator?

Yes, put one on the belly at the bottom of your fuel selector. This would be a drain in addition to the one on your gascolator. The fuel selector has a small plug in the bottom of it (1/4 NPT I believe). Directly below the fuel selector, the belly of your plane should have a removable button plug approximately centered under the plug in the fuel selector. Pop the button plug out and replace the plug in the fuel selector with a SAF-AIR CAV-110H-4 fuel drain valve (it has the same thread size). This model of drain valve has a small extension tube that will extend below the belly a bit so if it ever drips, it won't drip into the belly. Drill a hole in the button belly plug to accommodate the extension tube on the drain valve and re-install the button plug, and you're done. It's one of the easiest things you can do. Recommended whether or not you have trouble with water in your tank, as it gives you a drain at the lowest part of your fuel system.

Love this forum, I learn so much.

I did not know the fuel drain valves were available in stainless.

I don’t have a drain valve under my fuel selector but might install one.

reecewallace wrote: Do I need to replace the gasket too?

Yes. Bruce made some templates here to manufacture these gaskets yourself.

reecewallace wrote:...
These are the parts & supplies I'm ordering from Aircraft Spruce:
...- 6 reservoir screws MS35207-264...

Are you trying to usurp my title of Chief Skinflint? (It's part of my Mennonite DNA). Even Scotsman Jim might suggest you replace parts on both filler necks. Or is one wing getting a lot more rain than the other?

Jim, as usual, is right. Using PRC as a sealant overkill. But that junction between the filler neck and the moat will be underwater all winter up there. It does need some sort of sealant. It's most likely that water is getting in through the cap gasket if that hasn't been replaced in years. I was curious how much higher the neck was than the tank cover. Looks to be less than .040" Here's a picture:There are three gaskets in this assembly. The thicker any of those three gaskets are, the lower the filler neck will be relative to the top of the tank cover. The point being thicker is not necessarily better in this application. As it is water in the moat will find its way into the tank through capillary action if you have a poor fuel cap gasket.

It's interesting that Cessna's solution to this problem on the C-180 floatplane was to add a drain to the moat. Here's SK8054-1: Reece, the best advice I can give you is to take Jim up on his offer to meet him at YPK. Changing out the gaskets on those tanks is a PITA. Let Jim do it! Before you go though follow this advice from Monarch Fuel Caps

- Use a quality penetrating oil for 5 days before you remove old filler necks

With most old filler necks the original Cessna screws oxidize and corrode very bad. We recommend that you remove the paint over the screws and apply one drop of quality penetrating oil (NOT WD40 ! WD40 is a water displacement product) on each screw and also on the screws attaching the filler neck to the fuel cell. If you do this each day for 5 (five) days this will yield better results than trying to do it all the same day. You will give the penetrating oil time to break up the oxidization and corrosion. The screws should come out easier with fewer broken and deformed heads. This will reduce your installation labor costs.

The best penetrating oil is Mouse Milk which is available from aircraft parts supply providers.

Thanks for this gasket information, very wise and money saving.

My retired AME friend recommended the same thing, but it's great to have a template. I'll print it off and cut it out. 1/16" cork, correct?

We're only going to be doing the gas tank gaskets. I only seem to get water in one tank, but might as well replace them both while we're at it.

Too bad the Monarch caps aren't approved for C-170/172 aircraft.

You’re going to find out its a ton of work. From memory, as I understand it there’s really only one gasket that’s sealing water from entering the tank, that’s the one inside the tank. The two cork gaskets are there to provide fretting / dissimilar metal protection. One, between the tank wing access panel and the fuel tank well. Second, between the fuel tank top and fuel well bottom mating surface. I thought Jim Wildharber had made a good presentation of the process of replacing these gaskets. It’s hidden here somewhere.
Success here will be measured by how easily the screws come out of the wing panel fuel tank access panel, a direct function of when they were last removed and more importantly how the screws come out of the filler neck adapter.
Really take you time, use mouse milk like its free, and here’s hoping good success.

c170b53 wrote:You’re going to find out its a ton of work. From memory, as I understand it there’s really only one gasket that’s sealing water from entering the tank, that’s the one inside the tank. The two cork gaskets are there to provide fretting / dissimilar metal protection. One, between the tank wing access panel and the fuel tank well. Second, between the fuel tank top and fuel well bottom mating surface. I thought Jim Wildharber had made a good presentation of the process of replacing these gaskets. It’s hidden here somewhere.
Success here will be measured by how easily the screws come out of the wing panel fuel tank access panel, a direct function of when they were last removed and more importantly how the screws come out of the filler neck adapter.
Really take you time, use mouse milk like its free, and here’s hoping good success.

It’s hidden in MX Library - Fuselage, wings, and Tail section. Topic: Fuel Tank Removal ( ‘55 170B)