8KCAB Gascolators and firewall fittings

[Big Ed]

Have a leaky gascolator. Looks like it is where the inlet fitting enters the cap. Aircraft goes in for annual today, so I would like to discuss upgrade/improvement options with my A&P/IA.

1. That firewall penetration seems sketchy. Fuel is getting thru the gap, which means burning fuel would get thru. What options do I have to correct?

2. Some have mentioned Steve's Gascolaotors as an upgrade. What are the benefits?

 

[Bartman]

best bet is to either try Texas Air Salvage for that fitting I was telling you about or see what the factory has to offer. Steve's might have their own version of the fitting, I don't know.

 

[Bruce]

Is this in the center of the fire wall or to one side? If it’s centered I may have that fitting but alas I’m in Wyoming won’t be back to Tn for 2 months, I’ve moved mine to left side of aircraft to eliminate the fuel line behind the rudder pedal. It was half crushed by a lot of left rudder go figure.

 

[Big Ed]

Left side of firewall.

I talked to ACA today. They have a flanged thru fitting, but it is sized to fit their current gascolator, which is 1/2 NPT. The old one, which I believe I have, is 3/8".

It looks like my fitting does not match the parts manual. I have a single elbow fitting. The parts drawing uses an elbow, washer, and nipple. I think the combo of elbow and nipple allows the washer to be tightened against the firewall to seal the gap.

I'll discuss solutions with my A&P tomorrow.

 

[Bartman]

that little fitting I showed you looks homemade but it was what they were using. Texas Air Salvage is parting out Citabrias so they might have one.



This might be the fitting and washer you mentioned

Texas Air Salvage - used aircraft parts - aircraft salvage yard, aircraft engines, propellers, avionics and airframe parts.

Texas Air Salvage, offers high quality used aircraft parts for general aviation aircraft from manufactures like Cessna, Piper, Mooney, Beechcraft and more. We list thousands of aircraft engines, avionics, propellers and airframe parts complete with details, photographs, pricing and online...

texasairsalvage.com

 

[Big Ed]

This might be the fitting and washer you mentioned

Texas Air Salvage - used aircraft parts - aircraft salvage yard, aircraft engines, propellers, avionics and airframe parts.

Texas Air Salvage, offers high quality used aircraft parts for general aviation aircraft from manufactures like Cessna, Piper, Mooney, Beechcraft and more. We list thousands of aircraft engines, avionics, propellers and airframe parts complete with details, photographs, pricing and online...

texasairsalvage.com

Good find! Yes, that is the correct original fitting according to the parts manual. However, I just measured my fittings, and this one won't fit, because I don't have the original gascolator. My gascolator has a 1/2" inlet after all, so the new factory fitting will work.

Here is a pic from ACA. Gascolator side is 1/2" NPT, while cockpit side is 1/2" flare. Fitting is enroute.

Question: is there such a thing as an elbow with a female flared fitting on one side? The fuel line from the shutoff valve joins at a right angle, and already has a flared nut. Would save a bit of labor if I can just slap an elbow on it.

 

[Bartman]

a female flared fitting is, ironically, a nut, no?

 

[Hiperbiper]

Wow!
1/2" is huge...you sure it's not 1/4" npt with an AN6 flare fitting?
If you have an Aircraft Spruce catalog laying around they have a usable description of pipe thread sizes and related AN fittings.
Chris

 

[Big Ed]

Wow!
1/2" is huge...you sure it's not 1/4" npt with an AN6 flare fitting?
If you have an Aircraft Spruce catalog laying around they have a usable description of pipe thread sizes and related AN fittings.
Chris

We measured the male NPT end of the current elbow and the threads fit in a 1/2 box end wrench with no slack.

I browsed around Spruce and they don't seem to have that specific fitting. Doesn't seem like female cone fittings are a thing. Maybe the A&P will just have to fabricate a new flared line.

 

[Hiperbiper]

OK.
Not how to size NPT. If the dimension across the fitting is .560 it is indeed a 1/4" NPT . And MOST fittings in the Citibrthon aircraft that use 1/4" npt also use AN6 hardware...for instance a 90°aluminum fitting that adapts that 1/4" npt orfice to an AN6 flared fitting and uses a 3/8" line is a AN822-6D...a straight nipple for the same application would be an AN816-6D. It's hard to know what hardware is available unless you use it everyday.
If you go to Aircraft Spruce's webstore and go to "hardware" then AN hardware you should find what you seek.
With some of the older birds ( like mine) you'll find some Byzantine brass fittings that have been in use since WW1 but are now getting harder to find. The kicker is the pipe threads in the old stuff are a different pitch and not tapered so even though it will thread in it will in most cases, leak. If you have copper lines and brass fittings you've got the old stuff...
Hope this helps...

Chris

 

[Big Ed]

Well heck. At this point I'll probably just wait til I get the fitting on Friday and see if it fits or not. There is an aircraft parts store at Lakeland with a complete selection of AN hardware and fittings, so I can go there and see what is available.

 

[Big Ed]

Ok, I ordered this one from Aircraft Spruce as a backup. Says it has a 1/4" NPT fitting. https://www.aircraftspruce.com/catalog/appages/gascfirewallfitt.php

 

[Hiperbiper]

That should do it. Your gascolator screws onto the 1/4" npt side and the cabin side is an AN6 connection...just make up the 3/8" aluminum line to wherever it goes to and you're golden!
One word to the wise; prior to drilling any holes in the firewall for the mounting plate, thread the mount into the gascolator and tighten to full torque...THEN mark and drill your holes to rivet it down.
I won't say who did it but someone once mounted one of these in a Glasair III. Did a superb job bonding it into the firewall, fairing it in and making it pretty. Like all the way thru paint pretty. Unfortunately; while installing the gascolator permanently it was found that when screwed down tight the stupid thing was perfectly horizontal.... So mock it up THEN drill the holes...

Chris

 

[Big Ed]

Any concerns about how far out the gascolator projects from the firewall on an aerobatic aircraft?

Haven't discussed with my IA yet, but wondering if he will have issues with the Spruce fitting if it is an experimental part and not AN spec.

What about using a reducer nipple on the ACA fitting? I guess it would have to be on both sides.

I might order the Citabria part from Texas Air just to cover my bases.

 

[Bob Turner]

Did not know that old brass pipe threads were not tapered. New ones are tapered, and I have surplus WWII brass tapered fittings.

Some of the older flare nuts are roughly the correct size to start into a pipe thread, but as Chris says, that won't work well at all. And some of the new Chinese flare nuts won't work well on flare fittings! For brass, look for Eaton fittings.

 

[Hiperbiper]

Any concerns about how far out the gascolator projects from the firewall on an aerobatic aircraft?

Haven't discussed with my IA yet, but wondering if he will have issues with the Spruce fitting if it is an experimental part and not AN spec.

What about using a reducer nipple on the ACA fitting? I guess it would have to be on both sides.

I might order the Citabria part from Texas Air just to cover my bases.

Talking to your IA is your best, first course. I will not presume to tell you what is acceptable and what's not. I'm not signing your logs...
As an aside, the ACA and AS-S parts look like they mount the gascolator in the same manner.
JMPO
Chris

 

[Big Ed]

Got the part from ACA. As predicted by Chris, it does not fit. Too big.

Unfortunately the Spruce fitting is on backorder.

I'll talk to my A&P about options. Maybe put it back together using the current parts, then update when the correct part comes in.

 

[Bartman]

I won't say who did it but someone once mounted one of these in a Glasair III. Did a superb job bonding it into the firewall, fairing it in and making it pretty. Like all the way thru paint pretty. Unfortunately; while installing the gascolator permanently it was found that when screwed down tight the stupid thing was perfectly horizontal.... So mock it up THEN drill the holes...

that is great advice! i'll have to check mine.

 

[Big Ed]

Got a couple of options.

First, and preferred by my A&P, is order the post from Texas Air Salvage. I'm going to do that.

I also found this part at the local aviation parts store. It looks like the right diameter, though I do not have the old part available to compare. The only issue is that the flare side seems too long, which will cause the fuel line to stick out from the back of the firewall, where it may get kicked.



Finally, searching for that part number turned up this at Wag Aero. Same part but shorter. https://www.wagaero.com/gascolator-firewall-fitting.html

At this point probably going to order the Texas Air and Wag Aero and compare.

 

[Big Ed]

Follow up ... need a little advice from those with more mechanical experience than me. Discussing options with my A&P/IA. We have a few days to order parts because they won't be done with spar inspection and engine repairs until later in the week.

I ordered the salvage parts from Texas air. Thanks for the find, Bart. Pics aren't available anymore because I bought it, but below are similar. The parts are an elbow with female NPT and male 45 flare ends, a short NPT nipple, and a washer. The nipple threads into the gascolator, goes thru the firewall, and into the elbow. The washer is trapped between the elbow and the firewall to seal the gap. The flare end of the fitting points towards the fuel shutoff valve.



Here is the issue I see with that setup. The gascolator must be vertical, while the elbow must point horizontally to the left, as shown below. What are the odds that the nipple and fittings will naturally wind up pointed that way? If the elbow is not oriented at exactly 270 degrees when tightened, it will have to be loosened or tightened further to achieve the correct orientation. Either could be problematic for maintaining a good seal.



That got me thinking about better alternatives. What about using the Wag Aero fitting, with a swivel elbow on the flare side? That would allow the NPT nipple to be fully threaded into the gascolator cap and tightened to ensure a good seal. The swivel flare nut would allow the elbow to be pointed in the correct direction and then tightened down. Everything would be tight, leak proof, and pointing in the right direction.