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Torque Tube Shims

Darrel Starr

Darrel Starr

Registered User
Plymouth, MN
I saw in Bill Rusk's Javron thread the tedious effort it takes to get shims in the bearing caps to set tension to limit torque tube movement. It reminded me that I elected not to go through that procedure and just set the bearing drag by tensioning the bolts. The bolts and new stop nuts hold the tension just fine and allow for simple fine adjustments to the bearing clearance as time goes on. I just turned the front bolts about a 20th of a turn to snug them up just right. I cant think of a good reason to fiddle with shims in this application where the relatively giant bolts and nuts carry virtually no load. I wonder if Piper was thinking about engine connecting rod caps when they put shims here. Anyway, 340 hrs later and all is well and convenient for future tweaking. So do others leave the shims out or am I all alone on this one?
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If you are experimental I guess you could do this; but if certified you must use the shims in order to achieve "proper torque".

"All bolts are to be tightened to a specified torque as given by the manufacture and if none is available you would refer to the standard torque chart in AC4313-1B Table 7-1."

On your "set up" with that type of hardware; you can not torque it properly, and still be able to move the tube.

Getting the proper shims located and installed is a bit of a pain but a necessary one.
 
Thanks Ed. My view is that these large bolts are "adjusters" and there is no point in torqueing them up tight. Sort of like cases other places in the plane where bolts are used more as pins then as bolts that require tensioning. In this application there really is no point in torqueing to reach a certain bolt stretch since the bolts aren't working in tension. But again, you might have a different opinion.
And here is another thought, I wonder how many of these perhaps once-upon-a-time were torqued but now no longer have any significant bolt tension -- doesn't really hurt anything to have the tension relax so no one ever checks it.
 
Darrel Starr said:
I saw in Bill Rusk's Javron thread the tedious effort it takes to get shims in the bearing caps to set tension to limit torque tube movement. It reminded me that I elected not to go through that procedure and just set the bearing drag by tensioning the bolts. The bolts and new stop nuts hold the tension just fine and allow for simple fine adjustments to the bearing clearance as time goes on. I just turned the front bolts about a 20th of a turn to snug them up just right. I cant think of a good reason to fiddle with shims in this application where the relatively giant bolts and nuts carry virtually no load. I wonder if Piper was thinking about engine connecting rod caps when they put shims here. Anyway, 340 hrs later and all is well and convenient for future tweaking. So do others leave the shims out or am I all alone on this one?
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Darrel your a rebel that makes alot of sense. just because a bolt is a certain size doesn't mean it has to be torqued to a specific setting. Top landing gear AN6 bolts with ski tabs are happy just snug.

Glenn
 
Me too. Shims are easy to make, but most Cubs get cinched down so tight that it is difficult to move the ailerons. I discovered your trick in 1962. I would not dare use that trick on the South Bend headstock. Sometimes you have to use a little common sense.
 
In the days that the Cubs were built CAM 18 was the book to follow. This is from CAM 18, 18.30 (5) ..."Nuts should be torqued in all important places, such as wing-joint bolts, engine-support bolts, landing-gear bolts, and the like."

I have emphasized should. It does not say must. It implies that some judgement should be used as to whether a torque wrench should or should not be used. This is not the cap on a connecting rod in an engine. Sorry Ed, I'm with the other guys on this one. I think that the spacers are in there to prevent some ham fisted wrencher from over tightening thus making the controls too stiff.
 
I use the shims since I am signing it off and that is how Piper did it. Just takes a few minutes. That way when the pilot does something stupid and a bunch of lawyers look over the airplane I don't have to justify why I left a part of the control suystem out. Sorry, been there and don't like it.

Worked on some Cub Crafters data plate Cubs where the rudder and brake pedals were not shimmed. They eventually got loose, probably had paint in those areas, but not as easy to adjust those like the torque tube.
 
I agree with Steve that if Piper installed shims then they must be there. It is the torquing that is optional.
 
There is hope for the country; Bipartisonship will reign; Mike & I agree on something.

Glad there is some support out there for not installing shims because yesterday I took all the shims out of a friend's J-3, installed new nuts, washers & bolts. He wasn't so sure this was a good idea but he liked the feel after getting the bearing clearance reduced. He is 82 & still gets the J-3 out for a ride on nice mornings. Now I can show him the responses from experts on SC.org so he will feel better about this setup.
 
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I do take a few more pains on the rudder pedals. If you really like shims, brass can be had down to about .002. I do not think Piper just slammed shims in there - shims are sort of an "as needed" part, rather than an essential component.
 
Looks like Steve and I are in the same boat on this one.

I agree that the system will work "OK" doing what your doing; but as an IA I must follow certain guidelines in order to avoid the potential consequences. .
I can not think of any argument that the FAA or any judge would accept for my leaving these out; or signing off one that doesn't have them.
If done properly the shims will work fine, and you can have the bolts snugged up as they should be.
 
I don't see what you are gaining by leaving them out? Piper had a reason for everything they did, so I would figure they had a good reason to put them in.
 
I think you could leave the shims and the bolts out and sort of glue everything together with Herculiner. That would save a few ounces for those guys that are looking to shave some pounds off, a two-fer.
 
When you cut a piece of perfect circle pipe in half with a hacksaw the thickness of the hacksaw blade is missing, use the shims. Does it make a difference? I doubt it. Im sure when piper did it the halves probably werent cut exactly the same everytime sometimes even when fully tightened there was some slop. So they were probably made a little undersized and then shimed up to fit.
 
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Yes, but do you know for sure that there was one, and only one, shim installed by Piper in each and every one of these interfaces? Seems to me that shims, by definition, are an "as needed" item. If an IA is forced to do exactly as Piper did, there are a whole lot of stop nuts that will need to be replaced with castellated.
 
Two different situations. Put some shims in and kinda sorta fill the gap then snug up the bolts not quite bringing the shims up solid -- the legalese approach; nothing wrong with doing this and it serves a purpose but in the end it doesn't matter if the shims are there or not.
Or, the rigorous method: torque bolts, measure the gap, put in shims you think will come up solid just as the bolt torque is reached and the clearance is perfect. Do this over & over until you finally hit the magic combination, which will last only until some wear takes place. With some perseverance this can be done and might be what the Piper engineer had in mind. I think quite a few people take the first approach and very few the second one. The second group includes Bill Rusk's friend working on Bill's plane - this is the right way to do it if you believe shims have some importance.
Or just forget the shims and set the clearance to match the stick feel you are looking for.

Addressing the idea that the Piper designer put shims there for a good reason --- The Cub/Super Cub is a great design but like all machine designs, along with the truly ingenious details there are some monumental bone headed screw ups -- take, for instance, the trim crank mechanism. No bearings so the thin supports from the frame wallow out and the funny cone shaped spring eats through the cover plate. Maybe the same designer decided to put shims in the torque tube caps. Some of these weak spots in the overall iconic machine design just shouldn't be replicated when the plane is rebuilt.
 
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bob turner said:
Yes, but do you know for sure that there was one, and only one, shim installed by Piper in each and every one of these interfaces? Seems to me that shims, by definition, are an "as needed" item. If an IA is forced to do exactly as Piper did, there are a whole lot of stop nuts that will need to be replaced with castellated.
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I guess I can speak to this one; as back in the late 60s early 70s we were converting brand new cubs (less than 30 hrs ferry time) into sprayers with internal fiberglass hoppers. In doing so the torque tubes were removed during the process. You learned quickly to keep the shim sets in exactly the location where found as they are all different. Piper had the tubes adjusted to where they move smoothly and no slop. The bolts were always tight.
 
The caps are made out of 1.5 inch id tube and the torque tube is made out of 1.5 inch od tube, so when piper cut the tube for the caps, they have in there print as a .063 cut with the blade, so the shims are used to correct that and any other things that werent exactly perfect. Im just guessing but thats probably why they used shims and also not wanting to send anything out with loose bolts.
 
Darrel, what's going to "wear"? I'm pretty sure piper never painted the rudder pedals and the u shaped brackets that hold them on. I just took my floorboards out, 1968 original, never removed, and they weren't painted. My torque tube appears to be in the same condition, it was not painted, nor were the caps that hold it on. It looks like in your photo that yours is painted, which eventually would wear in and change the size. What was the reasoning behind painting that surface? I cleaned the old cruddy grease out of mine and it feels so much better.
 
My airplane was pretty much stock when I bought it in 1962. It had one shim on each surface, and the ailerons were stiff. They had obviously worked fine for a decade and a half, and I soloed the thing with stiff ailerons. Then one day I took a half-turn off each bolt, and ever since have enjoyed delightful aileron control. I have plenty of brass shim stock here, if this ever becomes an issue. The original Piper shims are still in there.
 
Yes, I see too in my photo that I probably didn't take the powder coating off the bearing surface. Would have been better off with no paint in there. In 340 hr. The only adjustment I've made was to the front cap. Turned those bolts just a scoach. Would be smarter to have taken paint off & have a clean smooth bare metal surface.
 
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Looks like I turned the cap around or mixed up front & back ones - I'll look into it.
In my defense, I did this work back around 2003 when I was an inexperienced 60 yr old kid.
 
Just another reason I am glad I have an experimental aircraft, shims or no shims it really is never going to matter in this particular location.

I did mask the bearing surface off though and stamp the caps as they came off the towers.
 
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