Torque Tube Shims

[Steve Pierce]

I don't understand the big deal here. Takes a few minutes to get the shims correct and it is done. That is the way I do it. I see a lot of liberties taken with the rebuild of these airplanes after rebuilding several that had never been apart. I have a respect for Piper and how they did things. As far as legality I doubt the FAA will ever say anything but after being deposed twice, sued over a midair where the other pilot was killed and had the FAA peruse a groundless enforcement action for 5 years and then drop it a few days before an NTSB hearing I have gained a little insight into how things work and chose to pass this on to others so maybe they can learn something from it without having to go through it themselves. If you don't like the shims I'll pay the shipping and will use them.

 

[skywagon8a]

This has been an interesting discussion of to shim or not to shim and to torque or not to torque. The bottom line seems to be that Piper used shims to prevent over tightening of the stick control torque tube which could cause a control issue in flight.

Steve what do these Piper shims look like? Are they a special shape and thickness? Or are they just a stack of special washers? I think that regular AN960 washers have a diameter which is too large for this use.

 

[tempdoug]

http://www.univair.com/piper/parts/u41371-003-piper-attachment-shim/

 

[RAC cubs]

So after all this care about shims ,do you take them apart and clean and lube every year or two? just worked on a Husky they have grease zerks there.but nothing like taking them apart and cleaning and looking at everything.but then there are people that use (FLY) their planes and ones that don't .

 

[PerryB]

Mine has oil holes in the caps. I give them a drop of Kroil in the hole and another on either front corner of the saddle at annual. It wicks right in and works great.

-- I support shimming/tight bolts. Its not that hard to do.

 

[RaisedByWolves]

This has been an interesting discussion of to shim or not to shim and to torque or not to torque. The bottom line seems to be that Piper used shims to prevent over tightening of the stick control torque tube which could cause a control issue in flight.

Steve what do these Piper shims look like? Are they a special shape and thickness? Or are they just a stack of special washers? I think that regular AN960 washers have a diameter which is too large for this use.

 

[Darrel Starr]

There that looks better:
The front cap is on straight and has fatter welds so at least I didn't swap them. Turned the rear cap around; parting line looks straighter to me.
Stick feel is unchanged from before.

 

[Steve Pierce]

I put a single pick mark on the cap and the front fuselage fitting at disassembly and two pick marks on the rear so it all goes back together correctly.

 

[Darrel Starr]

Good idea Steve, will mark the caps next.

 

[skywagon8a]

Here is the shim drawing no. 41371 
http://www.supercubproject.com/drawings/pdfs/A3290351.pdf

 

[flybynite]

Torque? Shims?
Problem solved.



Oh, yeah, testing a new kevlar aileron cable too.
(Darrel made me do it)

Wayne

 

[Steve Pierce]

Reminds me of the Super Cub with the pilot seat held in with a rope.

 

[Mauleguy]

Kinda telling... how the guys who worry about "blue printing" their parts don't understand the base/actual functional needs of them....

Common sense looking at how the part functions, this is not the same as a connecting rod or main journel where clearance and torque are required to be maintained. It was about setting the tension to what I like for the stick if I want it a little more it is easy to accomplish or a little less. Could it have been accomplished by shimming it, Yes but did it need to be done that way, not really.

I am a machinist and deal in tenths of thousands everyday and have done years of mechanical work, enough to know in this particular example a shim is not required for safety of flight. Just because piper did it that way does not mean it has to be if you are an experimental aircraft builder.

I have heard many stories from people that deal with the FAA and what is required to satisfy them during certification. It is just as likely they were put in this place only to satisfy the FAA and not for any other reason. If I was a certified aircraft owner or a AP working on a certified airplane I would put them in for one reason, it was built that way. Because I fly experimental I can do what I want.

 

[Mauleguy]

Kinda telling... how the guys who worry about "blue printing" their parts don't understand the base/actual functional needs of them....

Please explain to me since you see something I am missing in this example of why these shims are base/actual functional need... And don't say because Piper did it that way. I am looking for a reason.

 

[skywagon8a]

Please explain to me since you see something I am missing in this example of why these shims are base/actual functional need... And don't say because Piper did it that way. I am looking for a reason.

I suspect that they are there to prevent some ham fisted wrench turner from over tightening, which could cause too much resistance to moving the controls. Thus an accident could be prevented.

 

[Cub junkie]

I don't have an answer in regards to why the shims are there if there is proper torque and fit on the bearing clamps. I do know Piper has been sued for some really frivolous things.

 

[Mauleguy]

I suspect that they are there to prevent some ham fisted wrench turner from over tightening, which could cause too much resistance to moving the controls. Thus an accident could be prevented.

That could also play out the opposite way, will just tighten until the bolts are torqued down. The old shims are there and will give the proper tension on the caps! NOT.... I suspect that some airplanes have more shims then others since this is far from a precision machined part. In fact if it was to be shimed properly it would need to be done with various thicknesses of shims and then you would need some way to measure the resistance or have a clearance requirement that is done with plastigage. But that is back to my main point of this is something that is not really needed. Just my opinion, I will wait for a good reason to do the shims on my experimental airplane.

I have to get back to reading blue prints and making parts now so the debate will have to wait.

 

[skywagon8a]

Here is the shim drawing no. 41371 
http://www.supercubproject.com/drawings/pdfs/A3290351.pdf

I suspect that some airplanes have more shims then others since this is far from a precision machined part. In fact if it was to be shimed properly it would need to be done with various thicknesses of shims and then you would need some way to measure the resistance or have a clearance requirement that is done with plastigage. But that is back to my main point of this is something that is not really needed. Just my opinion, I will wait for a good reason to do the shims on my experimental airplane.
I have to get back to reading blue prints and making parts now so the debate will have to wait.

I agree with you. Take a look on the drawing. There are three different shims.

 

[Steve Pierce]

AR is "as required"

 

[wronghand]

I would hazard a guess Mauleguy, that a torque wrench and plasti guage was probably what was used back in the day at the Piper factory. Make every one the same clearance, repeatability, machinist/manufacturing stuff. Having said that, I think I will do it your way when I get that far on my experimental. "Snug em up, see how it feels". With nyloc technology I think the torque tube will not be falling off in flight. Thats the beauty of being experimental.

 

[musket]

Just as an FYI, the Piper dwg for this shim (41371) lists three variants http://www.supercubproject.com/drawings/pdfs/A3290351.pdf

however if one goes to the UNIVAIR site, one will find that they have a 41371-005 which is a 'peelable' shim -- whose layers are ~.002" thick. http://www.univair.com/piper/piper-j-3/view-all/41371-005-piper-peelable-shim/ and http://www.univair.com/piper/piper-j-3/view-all/u41371-005-piper-torque-tube-bearing-shim/ If one orders some of these, you probably should keep them somewhat separated from the other shims, 'cause they are difficult to discern the layers, and to separate them.

 

[KeithO]

An old thread - but it didn't make sense to me to start a new one.

I have a torque tube with up/down play in it. In other words, I can pull vertically up and down on the front control stick and feel the hits against the saddle. It does not feel terribly bad, but I can also see a gap between the tube and saddles. The saddles do have shims installed.

I'd like to tighten it up so that there is little if any "last" in the system. And I intend to torque the cap bolts to spec.
I looked for the Univar "peelable shim but could not find it.

Does anyone know of a source for the peelable shims or do I order the a few different thicknesses and mix and match to eliminate the play?

 

[skywagon8a]

An old thread - but it didn't make sense to me to start a new one.

I have a torque tube with up/down play in it. In other words, I can pull vertically up and down on the front control stick and feel the hits against the saddle. It does not feel terribly bad, but I can also see a gap between the tube and saddles. The saddles do have shims installed.

I'd like to tighten it up so that there is little if any "last" in the system. And I intend to torque the cap bolts to spec.
I looked for the Univar "peelable shim but could not find it.

Does anyone know of a source for the peelable shims or do I order the a few different thicknesses and mix and match to eliminate the play?

If your shims are too tight, sand them down or remove them all together. Tighten the bolts to remove the undesired slop. Nothing else needed.

 

[Steve Pierce]

I would check what you have. Might be as simple as removing a shim that is already installed. The shims are available from Univair and are called out in the parts manual if memory serves me correctly. They are not peel able however.

 

[Gary Raser]

Could someone tell me the difference in function between the J-3 torque tube and the PA-18. I am building an experimental cub. And have a J-3 torque tube assembly I was planning on using. I started with Wag-Aero drawings but have switched to pretty much PA-18 drawings and I am get a lot of parts from Javron
Thanks

 

[BC12D-4-85]

^^^^ The J-3/PA-11 rear stick moves a control rod attached to a rear bellcrank to move the elevator cables. The PA-18 setup moves the cables directly. Or something like that.

J-3, see page 26: https://www.univair.com/content/partcatalog/J3PM-flipbook/j3pm.html

PA-18, see page 141 on: https://www.univair.com/content/partcatalog/18PM-flipbook/18pm.html

Gary

 

[Steve Pierce]

Could someone tell me the difference in function between the J-3 torque tube and the PA-18. I am building an experimental cub. And have a J-3 torque tube assembly I was planning on using. I started with Wag-Aero drawings but have switched to pretty much PA-18 drawings and I am get a lot of parts from Javron
Thanks

J3 torque tube is taller and takes more stock force to move with a big engine. The early Super Cubs used the J3 torque tube and then they later went to a shorter torque tube and stick stub.

 

[Paul Heinrich]

I always thought the shims were shaped the way they are and placed to evenly distribute the cap bearing load and to prevent over-tightening. Wouldn’t it be disastrous if the cap was riding on one edge rather than flat - and the proper “feel” of the stick could be the edge of the cap slowly sawing through the torque tube?

Note: I’m usually wrong.