Leaking Gascolator Seal

How to keep the Cessna 170 flying and airworthy.

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Bruce Fenstermacher
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Re: Leaking Gascolator Seal

Post by Bruce Fenstermacher »

Reese, 1/8 NPT is a size and thread count. The letters of the acronym NPT stand for National Pipe Taper but the full name is American National Standard Taper Pipe Thread. As is the case for all pipe thread, 1/8th in this case, is the inside diameter of the pipe. The thread count is always the same for a given pipe size, there is no fine or course thread.

I feel pretty confident that your gascolator takes a 1/8" NPT valve. BTW I didn't picture them but valves are also available in !/4" NPT and a few other thread types.

Most people I think, when checking a gascolator, want to push it in for a second and release it and have the valve close. At some point you might also want the valve to stay open without holding it to drain the gas tank and so a locking feature would be in line. The CCA-1550 and the CCA-7450, are the same in this regard, you push straight in and release straight out and it opens and closes. However, if you push in and turn, the valve will open and lock until you turn it to release the lock. The major difference between the two are the 1550 has a stem out each side and the 7450 has a longer single stem out one side, which is used to open the valve. There are advantages and disadvantages to each style and I've cussed at both of them.

The other valves I pictured either have a twisting motion to pull them in (1250) and to lock or they have no lock feature at all (36150). Some of them (9950) have a hole drilled in the body for a lock wire.

I'm sure plenty of 170s have a CCA-1250 installed. I've cussed at these as well. But my personal choice would be either the 1550 or the 7450.
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Re: Leaking Gascolator Seal

Post by reecewallace »

Bruce Fenstermacher wrote:More about Curtis valve that might be suitable for a 170 gascolator application. As I have reported the CAA-7450 is the Curtis valve called out in the B model IPC. I'm sure I've used other valves and now with a job that has a parts department in which I get to rummage for parts, I've notice that lots of these valves look the same though they have different part numbers. So what is the difference. Here is a part of a Curtis chart that shows most of their 1/8 NPT valves with an install height of .75". As you can see the differences in each might be the material the bodies are made of, aluminum, brass, cad plated brass and so on. The other differences are whether the valve can be locked open and whether the action spirals to lock or is pushed straight down then twisted to lock or maybe there is no lock at all. You will note the CAA-7450 is made of cad plated brass and is a push to open then turn to lock valve with only a lever on one side. I might prefer a CAA-1550 which is brass, has the same open and locking action, but has a lever out both sides which might make it easier and more positive to operate with a fuel sample tube as a tool. Of course both levers would have to clear the gascolator, but I'd think this probably wont be an issue
Bruce—here are some photos of my exact gascolator. I think the CCA-7450 will work fine.

I also need the gascolator gaskets (top & bottom). Mine appear to be home made from cork, and they've completely worn out. In the 170b parts book, the number for the top & bottom seal are 0511199-6 which I couldn't find.

I found the alternate p/n 33-199-6, but they're $47 CAD, OUCH!

Is there a cheaper replacement for p/n 33-199-6? I read somewhere fuel cap gaskets may be suitable, but the dimensions are not exactly the same.
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Last edited by reecewallace on Tue Jun 15, 2021 1:06 am, edited 1 time in total.
- Reece
1956 Cessna 170b
Nanaimo, BC Canada
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Re: Leaking Gascolator Seal

Post by GAHorn »

See the post I made on this: viewtopic.php?f=24&t=14560&p=145668&hil ... ts#p145668

The genuine Cessna Gascolator Gasket PN is: 33-199-6

Change the PN in your Parts Catalog to the supereded PN: 33-199-6

If you LIKE the $45 price on EACH (takes two of ‘em so it’s $90 plus tax and shipping: https://www.iwantcessnaparts.com/Home/P ... d=33-199-6
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Re: Leaking Gascolator Seal

Post by reecewallace »

GAHorn wrote:See the post I made on this: viewtopic.php?f=24&t=14560&p=145668&hil ... ts#p145668

The genuine Cessna Gascolator Gasket PN is: 33-199-6

Change the PN in your Parts Catalog to the supereded PN: 33-199-6

If you LIKE the $45 price on EACH (takes two of ‘em so it’s $90 plus tax and shipping: https://www.iwantcessnaparts.com/Home/P ... d=33-199-6
Ouch, hell no! 8O

Thanks for the link. Sounds like 05-01059 is my best bet? My mechanic suggested 05-11187, but 05-01059 looks better like a more suitable fit as per your article.
- Reece
1956 Cessna 170b
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Re: Leaking Gascolator Seal

Post by c170b53 »

Interesting looks like your plane at some time in the past had a Doyn engine conversion.
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Re: Leaking Gascolator Seal

Post by reecewallace »

c170b53 wrote:Interesting looks like your plane at some time in the past had a Doyn engine conversion.
What’s that?
- Reece
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Re: Leaking Gascolator Seal

Post by Bruce Fenstermacher »

reecewallace wrote:
c170b53 wrote:Interesting looks like your plane at some time in the past had a Doyn engine conversion.
What’s that?
A Doyn conversion is installing a Lycoming 150 or 180 hp engine in place of the original Continental. I don't know what Jim sees in your pictures to make him think so. Maybe a cold snap in BC or something? :lol:
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Re: Leaking Gascolator Seal

Post by GAHorn »

Let me add something to the discussion on these gascolator gaskets.... The widespread confidence in rubberized/vulcanized cork gaskets for home made solutions to the ridiculous Cessna pricing on their PN 33-199-6 gascolator gaskets has led some owners to use cork as a remedy.
The problem as I see it is that without knowing the mfr’r or the source of the gasket material might be hazardous. I am speaking from personal experience. About 15 years ago, during an apparent shortage of the Cessna part, I switched to cork gasket material because that’s what my Aeronca used....which led me to believe that cork would work for this application also.
Unfortunately.... or Fortunately,... I had a work-related situation that prevented flying my airplane for almost 3 months, and as many of you may recall, I am a proponent of turning the Fuel Selector Valve OFF during storage.
As I prepared for a flight in N146YS after that 3-month period, I forgot during pre-flight to turn the Fuel Selector back ON for the pre-flight inspection...and as I squatted down to drain the gascolator I was reminded the valve was OFF because I was only able to drain about 2 or 3 tablespoons of fuel from the gascolator. So I returned to the cockpit and turned the Fuel Valve to ON.... and returning to the gascolator I observed a constant flow of fuel running out of it.
NOPE.... NOT the drain-valve.... it was the upper Cork Gasket that I ASSUMED had lost it’s “sealing” capability...perhaps by having dried out (was my initial thought) as it must have been ABOVE the fuel level in the gascolator.
DISAPPOINTED as heck.... I now had to delay my departure while I cut new gaskets from the remaining cork sheet I still had.

But the FORTUNATE thing about this episode is that when I disassembled the gascolator I discovered the LOWER cork gasket had turned to MUSH. 8O

That lower gasket was submerged in AvGas for 3 months and was clearly not a suitable material. The 3 months of non-activity was not the problem...it was the AvGas which dissolved the rubber which was the formative vulcanizing compound for the cork. As I handled the damaged gasket I became aware that the individual cork granules were still firm ...but the black rubber vulcanizing which solidifies the cork granules into a sheet during the vulcanizing process was not suitable for gasoline. I’m glad this was discovered on the ground. (And glad the Fuel Selector Valve was OFF during storage because if that gasket had failed then all my fuel would be running throughout the hangar floor.)

.... which brings me BACK to the memory of when my Aeronca was sitting on the ramp at KCLL back in the early ‘80s and when I arrived at the airport for a days frivolity of flying the ol’ Chief... I discovered the airport fire-department hosing down the area beneath my airplane which had dumped it’s fuel. (The Aeronca had a brass fuel valve which I was reluctant to operate .... so I simply left it in the ON position continuously. At least, until THIS event,...and as Paul Harvey might say “Now, you know the REST of the story.”

So... looking at reecewallaces’ picture and seeing that cork gasket material brought all this back-to-mind. I DO NOT recommend cork for a gascolator gasket.

I also wish to warn folks that EPDM.... so-called “Silicone Rubber” .... is also a poor gasoline gasket. It rapidly deteriorates and changes dimension when constantly submerged in gasoline. It will lose it’s surface-friction and “shrink” away from the gascolator glass cylinder. BTDT also.

NITRILE is the proper gasket material for gasoline. (And I have no idea what that WHITE rubber is that Cessna makes their PN 33-199-6 from, but the Cessna Mx Schedule correctly has the gascolator gaskets replaced annually....and that may have prevented another hazardous failure...because as I resolved to use only the GENUINE PN after the above failures.... I became aware of how HARD and BRITTLE that “Genuine” part becomes. I don’t like that at all.... which is what led me to search for a better solution to this issue.

For the last 13 years I’ve used the gas cap gasket (FC2651, Spruce Item No. 05-01059, priced at $1.59) mentioned above and had absolutely NO PROBLEM. YMMV.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Re: Leaking Gascolator Seal

Post by daedaluscan »

Steves gascolator. I know its not original, or glass but it is beautifully made and worth it IMNSHO.
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Re: Leaking Gascolator Seal

Post by c170b53 »

Looks like a reinforcing angle on the belly skin consistent with early Doyn 0340 conversions Normally two running for and aft from gearbox to firewall. Then again maybe I’m seeing things ( just had eye one cataract done, man is that wacky) had to do something to improve my landings)
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Re: Leaking Gascolator Seal

Post by reecewallace »

GAHorn wrote:Let me add something to the discussion on these gascolator gaskets.... The widespread confidence in rubberized/vulcanized cork gaskets for home made solutions to the ridiculous Cessna pricing on their PN 33-199-6 gascolator gaskets has led some owners to use cork as a remedy.
The problem as I see it is that without knowing the mfr’r or the source of the gasket material might be hazardous. I am speaking from personal experience. About 15 years ago, during an apparent shortage of the Cessna part, I switched to cork gasket material because that’s what my Aeronca used....which led me to believe that cork would work for this application also.
Unfortunately.... or Fortunately,... I had a work-related situation that prevented flying my airplane for almost 3 months, and as many of you may recall, I am a proponent of turning the Fuel Selector Valve OFF during storage.
As I prepared for a flight in N146YS after that 3-month period, I forgot during pre-flight to turn the Fuel Selector back ON for the pre-flight inspection...and as I squatted down to drain the gascolator I was reminded the valve was OFF because I was only able to drain about 2 or 3 tablespoons of fuel from the gascolator. So I returned to the cockpit and turned the Fuel Valve to ON.... and returning to the gascolator I observed a constant flow of fuel running out of it.
NOPE.... NOT the drain-valve.... it was the upper Cork Gasket that I ASSUMED had lost it’s “sealing” capability...perhaps by having dried out (was my initial thought) as it must have been ABOVE the fuel level in the gascolator.
DISAPPOINTED as heck.... I now had to delay my departure while I cut new gaskets from the remaining cork sheet I still had.

But the FORTUNATE thing about this episode is that when I disassembled the gascolator I discovered the LOWER cork gasket had turned to MUSH. 8O

That lower gasket was submerged in AvGas for 3 months and was clearly not a suitable material. The 3 months of non-activity was not the problem...it was the AvGas which dissolved the rubber which was the formative vulcanizing compound for the cork. As I handled the damaged gasket I became aware that the individual cork granules were still firm ...but the black rubber vulcanizing which solidifies the cork granules into a sheet during the vulcanizing process was not suitable for gasoline. I’m glad this was discovered on the ground. (And glad the Fuel Selector Valve was OFF during storage because if that gasket had failed then all my fuel would be running throughout the hangar floor.)

.... which brings me BACK to the memory of when my Aeronca was sitting on the ramp at KCLL back in the early ‘80s and when I arrived at the airport for a days frivolity of flying the ol’ Chief... I discovered the airport fire-department hosing down the area beneath my airplane which had dumped it’s fuel. (The Aeronca had a brass fuel valve which I was reluctant to operate .... so I simply left it in the ON position continuously. At least, until THIS event,...and as Paul Harvey might say “Now, you know the REST of the story.”

So... looking at reecewallaces’ picture and seeing that cork gasket material brought all this back-to-mind. I DO NOT recommend cork for a gascolator gasket.

I also wish to warn folks that EPDM.... so-called “Silicone Rubber” .... is also a poor gasoline gasket. It rapidly deteriorates and changes dimension when constantly submerged in gasoline. It will lose it’s surface-friction and “shrink” away from the gascolator glass cylinder. BTDT also.

NITRILE is the proper gasket material for gasoline. (And I have no idea what that WHITE rubber is that Cessna makes their PN 33-199-6 from, but the Cessna Mx Schedule correctly has the gascolator gaskets replaced annually....and that may have prevented another hazardous failure...because as I resolved to use only the GENUINE PN after the above failures.... I became aware of how HARD and BRITTLE that “Genuine” part becomes. I don’t like that at all.... which is what led me to search for a better solution to this issue.

For the last 13 years I’ve used the gas cap gasket (FC2651, Spruce Item No. 05-01059, priced at $1.59) mentioned above and had absolutely NO PROBLEM. YMMV.
Thank for for my morning coffee story! Glad you were able to discover this on the air.

My gascolator has had a constant drip while my fuel selector is on from the valve, so I've now grounded myself until the new parts arrive to avoid a worse leak.

It also has cork gaskets and they're quite deformed upon removing them. As this is my first year of ownership of the plane, I have no idea when they were made or replaced, albeit they look old!

I've ordered the Spruce Fuel Cap Gaskets 05-01059 which I will replace them with on my glass Koehler gascolator.

Didn't know there would be so many stories and info on the topic, but glad to read it! :D
- Reece
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Re: Leaking Gascolator Seal

Post by GAHorn »

c170b53 wrote:Looks like a reinforcing angle on the belly skin consistent with early Doyn 0340 conversions Normally two running for and aft from gearbox to firewall. Then again maybe I’m seeing things ( just had eye one cataract done, man is that wacky) had to do something to improve my landings)
which eye? Does that side now touch-down more gently? :twisted:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
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Re: Leaking Gascolator Seal

Post by ghostflyer »

Steve’s gascolator is one of the best replacement parts I have seen. It’s well engineered and only one “O” ring to change . Easy to clean the filter .
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Re: Leaking Gascolator Seal

Post by DaveF »

c170b53 wrote:Looks like a reinforcing angle on the belly skin consistent with early Doyn 0340 conversions Normally two running for and aft from gearbox to firewall
My Avcon has the same stiffeners.
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Bruce Fenstermacher
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Re: Leaking Gascolator Seal

Post by Bruce Fenstermacher »

DaveF wrote:
c170b53 wrote:Looks like a reinforcing angle on the belly skin consistent with early Doyn 0340 conversions Normally two running for and aft from gearbox to firewall
My Avcon has the same stiffeners.
If my memory is correct, the Doyn coverserion became a Avcon conversion. There are several Avcon conversions.
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