Pretzel Yoke Disassembly

[6643]

Tye Hammerle » Sat Feb 05, 2005 12:55 am

Finally got that taper pin removed from the yoke hub. It's not a hardened pin so it drills pretty easy. Center punch and start out with a 1/16" drill bit move up one step at a time to one that just leaves a thin wall behind. Gripped the pin in the middle with a needle nose vise grips. Supported the hub and smacked the vise grips with a hammer and the pin popped loose.

The short vertical piece of the yoke tubing is held on in a very interesting manner. The engineer who thought that up was warped. See pictures. There are two rods with an 'L' shape at one end and threaded at the other end where a nut goes on. There are two plates on each end to keep the rods in place.

Really odd setup.

The tapered pin measures approximately .250" on the fat end and .225" on the skinny end. It is approximately 1.3" long.
[Editor's note: the taper pin is an AN385-4-10, 1/4" diameter by 1-1/4" long.]

Tye mbr#6449

N2180V-48-14409, N1887V-47-14067, N73096-46-10316, N72971-46-10172, N77045-46-11499, N2928N-46-13189, N58712-40 PT-17-[75-341]

[6643]

Tye Hammerle » Sat Feb 05, 2005 12:58 am

Here's a couple shots of the hub showing how the yoke sits in it.

Tye mbr#6449

N2180V-48-14409, N1887V-47-14067, N73096-46-10316, N72971-46-10172, N77045-46-11499, N2928N-46-13189, N58712-40 PT-17-[75-341]

[6643]

Tye Hammerle » Sat Feb 05, 2005 1:04 am

Couple of the nasty little taper pin after I destroyed it. Really should have a drill press for this to keep the drill bit parallel with the centerline of the pin. As it is with my battery powered drill I drilled at a slight angle and broke out the side of the pin.

I was surprised how easy the pin drilled. Just need to stay centered and go easy, light pressure, pull the bit out after 1/32" or so of depth and clear the shavings so it doesn't get bound and snap the bit in the hole (at least that's what my machinery handbook says to do and it worked).

Next thing I guess is to see where I can find tapered replacement pins.

Tye mbr#6449

N2180V-48-14409, N1887V-47-14067, N73096-46-10316, N72971-46-10172, N77045-46-11499, N2928N-46-13189, N58712-40 PT-17-[75-341]

[6643]

NC76220 » Sat Feb 05, 2005 2:53 am

Tye:

I might as well come clean to you, as you are probably the third human to "go the distance" with the pretzel yokes. I rebuilt mine about 4 years ago. Here is the story:

Pulling the pins was acomplished by TIG welding the tips of a special puller that I made, to the butt ends of the pins. That way the pins were re-usable. I have seen the pins, they are available from McMaster-Carr industrial supplies. If you do not have the catalog, get one. They have all manner of odd stuff that I am certain you will need.. To fit the pins properly you might need to buy a corresponding tapered reamer. Using nuts and bolts here is bush league.

I remade the center tube out of aluminum, with a different type of fastening other than the "J" hooks, I thought they were rather heavy.

I made replacements of the red plastic outer covers from 6061 T-6 and made new "Cessna" emblems at a bicycle headbadge factory. The result is a perfect, polished center. I will try to dig out the drawings for you...

I then replated the control tubes in Nickle (Chrome can cause cracks). I looked for Titanium tube the same dimension, but was unable to locate. I was going to make black leather wraps for the yokes, but my plastic was too good to mess with.

Yes, I am an obsessive weight freek, and my 140 weighs 875 LBS

Erik

I want to be the last guy to fly across the USA with no radio

[6643]

NC76220 » Sat Feb 05, 2005 2:53 am

Tye:

I might as well come clean to you, as you are probably the third human to "go the distance" with the pretzel yokes. I rebuilt mine about 4 years ago. Here is the story:

Pulling the pins was acomplished by TIG welding the tips of a special puller that I made, to the butt ends of the pins. That way the pins were re-usable. I have seen the pins, they are available from McMaster-Carr industrial supplies. If you do not have the catalog, get one. They have all manner of odd stuff that I am certain you will need.. To fit the pins properly you might need to buy a corresponding tapered reamer. Using nuts and bolts here is bush league.

I remade the center tube out of aluminum, with a different type of fastening other than the "J" hooks, I thought they were rather heavy.

I made replacements of the red plastic outer covers from 6061 T-6 and made new "Cessna" emblems at a bicycle headbadge factory. The result is a perfect, polished center. I will try to dig out the drawings for you...

I then replated the control tubes in Nickle (Chrome can cause cracks). I looked for Titanium tube the same dimension, but was unable to locate. I was going to make black leather wraps for the yokes, but my plastic was too good to mess with.

Yes, I am an obsessive weight freek, and my 140 weighs 875 LBS

Erik

Hi Eric,

I would be very interested in your drawings and hear about other areas where you have saved weight. I have also decided to make the red center covers out of aluminum but I haven't made any drawings yet. I've got two 140 projects and I'm open to ideas. I bought my dial calipers from McMaster-Carr's online store. I didn't think to order a catalog at the time. When I was in the Navy they were a primary supply house for a lot of good stuff.

Welding on to the pins to pull them sounds like a good idea. I'd like to see what your puller looks like. It'd be a lot easier than drilling. While I'm at it I think I'm going to have the yoke hubs measured and CNC data created so I can make new ones. Both halves seem to be the same so only one "pattern" would be needed.

875 sounds pretty light! If you want to take another 33 pounds off, titanium gear legs from xpmods.com should be on your list. They're not cheap though. They need 10 orders at $8k before they'll make them and get the STC. They already make them for 180's. I've thought about putting 170 or 180 gear legs on but they are thicker than ours and won't fit in the gear box.
Tye mbr#6449

N2180V-48-14409, N1887V-47-14067, N73096-46-10316, N72971-46-10172, N77045-46-11499, N2928N-46-13189, N58712-40 PT-17-[75-341]

[6643]

NC76220 » Sat Feb 05, 2005 9:20 pm

I will dig around the factory and see if any of my old drawings are still here. I made the covers with a CNC so had a 3D model somewhere.

I almost opened a mold to make these new, but they wanted a thousand bucks.

I just checked my W+B, I am at 886. forgot I added the metal prop. My ship is pretty spartan, only required instruments, no radio. I have an alternator which helps, and the heavy interior parts were left out. Ii left the landing light off. I have only pilot side brake pedals. When I can make something out of aluminum instead of steel, I do so. The control yoke parts are an example of this. Cessna did a remarkable job of making the 140 as light as possible, there is not too much fat on it. I do some little stuff like leaving the engine hoist ring off, stuff like this is probobly psycological advantage only, but it adds up to a bucket of steel at some point.

I want to be the last guy to fly across the USA with no radio

[6643]

Sam Breeden » Sat Feb 05, 2005 9:48 pm

Univair sells new pretzel style control wheels (exact copies) for about $30 a piece. However, they are intended for use on the Ercoupe and have larger hub castings. They can be swapped out with the original Cessna hubs once you get them off by drilling out the pins as mentioned.

Been there, done that.

Sam

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John C » Mon Feb 07, 2005 11:38 am

Sam Breeden » Sat Feb 05, 2005 9:48 pm
Univair sells new pretzel style control wheels (exact copies) for about $30 a piece. However, they are intended for use on the Ercoupe and have larger hub castings.

They're not "copies". The original wheel was made by Decker. Both Erco and Cessna used them as the OEM (along with Taylorcraft and maybe others). Erco bought 10,000 yokes to get a quantity discount. Whatever was not used in original production has passed down the line through the various TC holders to Univair. They are what is known as "new old stock". I expect Univair still has several thousand of them. The hubs are all the same, but Erco had theirs bored out to accept a larger shaft.

The taper pins are standard AN parts and are readily available.

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Tye Hammerle » Thu Feb 10, 2005 10:02 pm

I finally got that second taper pin out. I drilled a hole in the end of it centered as best as I could and taped it about 1/4" deep to 6/32. Screwed a 2" long machine screw into it, used a half inch long piece of tube and a couple of washers and a nut to try to pull the pin out with the nut pulling on the screw. That failed. Twisted off a couple of screws, high enough though that there was plenty to get it out to try again. Finally figured I needed a slide hammer, naturally I don't have one, so after some consideration I clamped the head of the screw in a vise and smacked the hub with a hammer a couple times and viola!, the pin let go. Same principle as a slide hammer just not as elegant.

Is the original yoke shaft chrome or nickle plated? The wear pattern where the panel bushing rides and the general surface condition of the shaft looks like it was.

[Editor's note: most shafts were cad plated with the exception of 1948 140s which were chrome plated. The cad plated shafts show a clear wear pattern.]

Tye mbr#6449

N2180V-48-14409, N1887V-47-14067, N73096-46-10316, N72971-46-10172, N77045-46-11499, N2928N-46-13189, N58712-40 PT-17-[75-341]

[6643]

Tye Hammerle » Sun Mar 20, 2005 9:56 pm

My brother is about ready to try milling a yoke hub ('46 pretzel style) and I need to provide him some material. What would be the best type/alloy material to use? I've got to do some reasearch on aluminum alloys.

Tye mbr#6449

N2180V-48-14409, N1887V-47-14067, N73096-46-10316, N72971-46-10172, N77045-46-11499, N2928N-46-13189, N58712-40 PT-17-[75-341]