Central Fuel Vent Remove ck-ball (split topic)

How to keep the Cessna 170 flying and airworthy.

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BWeathered
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Central Fuel Vent Remove ck-ball (split topic)

Post by BWeathered »

George,

Sorry for diverting this thread a bit. In another thread, you said

"Cessna tried a modification and offered it as a Service Bulletin/Letter: It drilled a 1/8" thru-hole in the goosneck to accept a thru-cotter and installed a ball, as a type of "check-valve" inside which rested on the cotter, with a plastic cap which had a reduced vent-hole on the fwd opening. The intention was that any fuel which rose up inside would lift the ball against the cap and stop the ejection of fuel. The problem was not a good one as the reduction in size of the hole was problematical to reduced venting capability in an imaginary icing encounter. So Cessna issued another letter authorizing the drilling of another 1/8" hole in the aft side of that curve in the gooseneck. This offered an alternative vent in the case of the blocked fwd-facing vent. It also allowed the fuel to spit out again. In fact, since that new hole was on the aft side, it was in a low-pressure area, and it was suspected of actually worsening the situation by siphoning fuel out the gooseneck and onto the cabin roof. It could be smelled inside. So Cessna issued a THIRD letter, revoking previous alterations of that gooseneck and restoring it to original configuration. They then changed the design of fuel caps to include dual-venting provisions, and required at least ONE of the new vented caps to be installed (on the RIGHT wing.


I Have looked for the third letter that reverts the gooseneck vent configuration back to the original, with no cotter pin holes or aft vent hole. I can't find it (thought it might be in SEB 92-27), so can you steer me to that, OR even better, can you describe the method the cotter pin and vent holes were to be plugged when the check valve kit was removed? Hoping the solution was not to replace the gooseneck vent with a new, unmodified one.

Thanks,
Brent Weathered, N9194A
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GAHorn
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by GAHorn »

Hi, Brent! As you can see I split this from the original thread to avoid the diversion. (No problems.) :wink:

Over the years many factory communiques were made more simply than now. The information to which I referred above came from memory having read it in obscure literature, but nonetheless was from a reliable (Cessna) source. I have made a cursory review of some of my materials and have not found it yet, but will continue to search for it.

An example of the casual letters issued by Cessna in the "good ol' days" is attached dated 7-24-53. As you can see, it would be considered informal and downright "sketchy" by todays standards. I'm using this SNL (Service News Letter) as an example of the type of service letter from which the vent information was found,.... so if/when I find it I'll post it...but don't think it's going to be a detailed letter such as is found in modern "Service Bulletins"...or that it will contain detailed info on how to perform the work. You'll see what I mean when you read how they recommended to accesss cowling screws when retrofitting spinners (which I will post in that other discussion-thread also.) No info on where or how to create those holes in the back plate...
SNL53SpinnerRetroft.pdf
Cessna Service Information Summary 170-172 Propeller / Spinner
(842.38 KiB) Downloaded 753 times
'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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BWeathered
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by BWeathered »

Thanks,George! I will happily take your word that such a note exists. I'm more interested in how those 1/8" holes they had you drilling in the gooseneck were supposed to be "rescinded"! :D Brent
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by BWeathered »

George, I had some time to do somemore searching and found this comment by you on yet another thread....


Re: Fuel vent relocation to wing

Postby gahorn » Fri Feb 27, 2009 4:20 pm
Plug the vent with JB Weld... or remove it and weld it (TIG).

The check ball is located within the first part (upper end) of the gooseneck and held in place with a pin or cotter to prevent it's falling down into the vent system. I have the service bulletins somewhere in old library. I'll try to locate them and post them.


This answers my question. thanks!

Brent
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by GAHorn »

If I were to undertake the removal of the gooseneck vent check-ball mod... I'd pull the rubber cap off and vacuum out the ball, then pull the cotter pin which held that ball from falling into the vent-system,... and use a piece of pvc hose (such as sold at Home Despot for ice makers and such or at the aviation dept at ACE Hardware) that fit snugly into the gooseneck.... push the hose down into the gooseneck to create a blocking-dam ... then mix up some JB-Weld and smoothly fill all the holes from the cotter and the aft-vent-hole. After the JB cures slightly... pull out the PVC.

The Cessna SNL didn't provide any of that, of course.
'53 B-model N146YS SN:25713
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An originality nut (mostly) for the right reasons. ;)
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by n2582d »

George,
I wonder if you didn't read about that in WD Thompson's book because I can't find any reference to a third Service Letter/Service Bulletin/Accessory Kit that does away with the check ball or seals up the hole in the rear of the vent. In 1954-56 there was a flurry of Service Newsletters, Bulletins, and Kits which attempted to correct this poor vent design. Most of these communiques centered on the C-180. The primary concern was not fuel being spewed over the fuselage but icing blocking the vent. Once the vent was blocked the vacuum would cause the bladder tanks to lift from the bottom. The pilot then would have an erroneously high fuel reading.

Here's a chronological outline of a select few of Cessna's bulletins concerning the fuel vent:

SNL 54-07-07 adds an AN960-416L washer in front of the check ball to keep the ball from sticking to the neoprene housing. It also calls for the vent hole on the back of the tube to be enlarged to a #40 (.098") hole size.

SNL 6-20-55 calls for a larger ball on the C-180 check valve.

SL180-2 dated 2/10/56 explains the danger of the C-180 vent being iced over:
Click to Enlarge
Click to Enlarge
SK8053-6 dated 7/19/56 adds the check valve to aircraft produced prior to when Cessna included the check valve on the production line:
Click to Enlarge
Click to Enlarge
SL180-11 dated 8-27-56, slightly over a month since SK8053-6 was issued, Cessna relocates the vent under the wing, just behind the wing strut.
SL170/172-9 and SK172-7 dated 5/16/57 makes this vent kit available to the C-172.
Click to Enlarge
Click to Enlarge
SNL8-18-58 gives advice on insuring the fuel vent is clear:
Click to Enlarge
Click to Enlarge
Last edited by n2582d on Sat Apr 07, 2018 12:01 am, edited 2 times in total.
Gary
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BWeathered
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by BWeathered »

gahorn wrote:If I were to undertake the removal of the gooseneck vent check-ball mod... I'd pull the rubber cap off and vacuum out the ball, then pull the cotter pin which held that ball from falling into the vent-system,... and use a piece of pvc hose (such as sold at Home Despot for ice makers and such or at the aviation dept at ACE Hardware) that fit snugly into the gooseneck.... push the hose down into the gooseneck to create a blocking-dam ... then mix up some JB-Weld and smoothly fill all the holes from the cotter and the aft-vent-hole. After the JB cures slightly... pull out the PVC.

The Cessna SNL didn't provide any of that, of course.

Yep, sounds like a good approach. I know I do not have the check valve kit installed. I am going to look for any holes tomorrow and if I find any I will fill them as you have described.

Thanks!
Brent
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by 170C »

Apparently Cessna wasn't sure what to do with the fuel tank vent. C-170's had them in the center of the cabin (I think the '56's did also). Then came the '56 172 and the vent got moved to the far left end of the left fuel tank, but still up on top of the wing. That lasted only for the '56 model and all 172's (and other high wing Cessna's) since have had the vent on the bottom of the wing, behind the lift strut. With as many 170's as were built, one would think Cessna would have figured out where the vent needed to be prior to 1957.
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by GAHorn »

I'm amused/astonished Cessna seems so concerned about vent-icing and increasing fuel-qty indications after prolonged flight.... in airplanes not approved for flight in icing conditions. :roll:

My predecessor's predecessor, Tom Hull, wrote a short bit about the gooseneck vent-holes in The 170 Book, pg 93 (4th Edition). He recommended that those with the holes leave them there if they had vented right fuel cap. I suspect his advice was written for a previous Edition of the Book and became moot when the vented right cap became required by AD. In any event, the aft-side holes did not stop fuel from vomiting out the gooseneck ...it only sent some of it aft by "venturi effect". It was a Band-Aid on top of a Band-Aid. :(

BWeathered wrote:
gahorn wrote:... I am going to look for any holes tomorrow and if I find any I will fill them as you have described.

Thanks!
Brent
Brent, Are those YOUR legs pictured on page 98 of (4th Edition) The 170 Book? 8)
'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: Central Fuel Vent Remove ck-ball (split topic)

Post by BWeathered »

[/quote] Brent, Are those YOUR legs pictured on page 98 of (4th Edition) The 170 Book? 8)[/quote]

Had to go back and look but, yes, that is me and my wife, Linda, leaning up against N9194A one paint job and several pants sizes ago! Nice memories of Tom Hull... we knew him and his wife, and we flew up to his memorial service after his accident. I have some funny Tom Hull stories I will share in some other thread.

Brent
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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by cessna170bdriver »

gahorn wrote:I'm amused/astonished Cessna seems so concerned about vent-icing and increasing fuel-qty indications after prolonged flight.... in airplanes not approved for flight in icing conditions. :roll:
My theory is that it's the same reason VFR pilots (not approved for flight in IMC) have attitude indicators and directional gyros: Just in case...
Miles

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Re: Central Fuel Vent Remove ck-ball (split topic)

Post by GAHorn »

cessna170bdriver wrote:
gahorn wrote:I'm amused/astonished Cessna seems so concerned about vent-icing and increasing fuel-qty indications after prolonged flight.... in airplanes not approved for flight in icing conditions. :roll:
My theory is that it's the same reason VFR pilots (not approved for flight in IMC) have attitude indicators and directional gyros: Just in case...
Well, part of my amusement is Cessna's caution in icing conditions is that "flight should not be continued.... as there is no way of determining the amount of fuel aboard."
'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: Central Fuel Vent Remove ck-ball (split topic)

Post by BWeathered »

Follow-up: I did inspect my gooseneck vent yesterday and found no holes, nor any evidence of filled holes. While I was in that neighborhood, I replaced the slip-rings and the fuel cap gaskets, too, and cleaned the top of the plane. There is apparently a low pressure area created on the back of the gooseneck at the aftmost tangent on the gooseneck itself that traps and retains a few drops of fuel any time some is ported overboard, because there was a very heavy dime-sized fuel stain there. I have always been careful to leave tanks completely full to avoid condensation, but I may leave them a few gallons down now to try to avoid any porting.

Brent
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