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Wheel Nut Cotter - There must be an Easier Way!

K

Kyle Boatright

Well Known Member
Every time I pull the wheels on one of the airplanes I dread putting the cotter back in the wheel nut. It generally takes a ridiculous amount of time (x2), and leaves me wondering why I don't see others complaining about it.

What I do is mark the wheel and nut to properly index the nut so the holes are aligned. Then I use a something (ex: the old cotter) to verify that the holes are properly aligned. I sharpen the new cotter so it self-aligns a little more easily as it passes through the hole on the back side of the axle.

And it takes forever. Or several minutes a side.

How do I make this process go faster?
 
I struggled too. I finally over sized the holes by a small amount realizing that this is nothing more than a safety device and not load bearing that needs a close tolerance…. Sure made life easier!
 
Use a slightly smaller diameter cotter pin ? Its just there to stop the nut loosening and falling off...
 
A better way?…

I like the design VW used in the sixties ( and prolly other decades ) where the axle nut was slit, and once you reached the desired torque you tightened a set screw which clamped the nut in position.
 
rmarshall234 said:
A better way?…

I like the design VW used in the sixties ( and prolly other decades ) where the axle nut was slit, and once you reached the desired torque you tightened a set screw which clamped the nut in position.
Click to expand...

Sigh…..sometimes I really miss my old VW bug.
 
It worked great for the non-driven wheels up front. The rear driven wheels used a 36 mm nut a cotter pin and is torqued to 450 ft lbs IIRC. No reason we couldn’t do the same on our non-driven wheels that are so small in comparison. There you go Anti Splat or Fly Boyz….a freebie.
 
Some axles seem to have a close tolerance hole for me cotter pin, others seem to be a little bigger and easier to insert. I also use a proper length pin, I believe it’s AN380-4-7? Or was it a -6? I pre bend the head but be sure the legs stay tight and not starting to spread.. doesn’t seem too difficult except the one I recently did that was close tolerance. Maybe next time I have a wheel off, I’ll measure what still size the holes are..
 
KeithO said:
Use a slightly smaller diameter cotter pin ? Its just there to stop the nut loosening and falling off...
Click to expand...

This was my solution. I use a piece of safety wire to “find” the holes in the axle and align the holes in the nut and using one size down than what’s called out for in the plans I can get the pin in with no pre-bend and not too much effort.
 
We build them . . . we can make them work.

Mconner7 said:
I struggled too. I finally over sized the holes by a small amount realizing that this is nothing more than a safety device and not load bearing that needs a close tolerance…. Sure made life easier!
Click to expand...

+1 Well said!

During CI last week the holes got enlarged on my -7 with a small file. The axle was particularly tight. A bent awl ensures perfect alignment. Much more satisfying now.

A continuing part of the improvement process.
 
I recall a thread a few years ago on the same topic. It seems like a design that's ripe for innovation.
 
Do you fell like you would need to tighten it more (nut further on the axel), to get the holes to line up? If that's that case, then drill holes in the same position one "flat" over then lightly sand some material off the nut so it turns one more flat when properly tightened. If its really off then you may need to go 2 flats or a complete 180 and use the same holes

Alternatively, there may be some shims available with MMC to use your same holes.
 
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I get it dang close and just run my 12" drill bit through it real quick. Seems to align everything perfectly (maybe even takes off an insanely small amount of metal) and the cotter pin fits pretty well. I then get a big flat head screw driver on the end of the cotter pin and give it a tiny whack with a hammer. Works every time.
 
Kyle,

Make a mild steel, headed clevis pin of the correct dia & height (a bit past the axle tubing ID). Drill through the clevis head with a 1/16 bit. THen run a piece of safety wire through it and wrap around the large nut to hold it in place after installing. easy peasy. If you think both sides need to be captive, make two of them, captured with the same wire.
 
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Fine "Tuning" The Axle Nut's Position

Not directly related to the Op's question, but has some bearing on the overall process.

If, when installing the axle nut, the "sweet" spot is not aligned with one of the holes, you can do this -

Since the nut is 16 pitch thread, that means that each round of advancement is equal to .06325" - and each "flat" advancement is equal to .0104" (call it .010).

So, if your estimate of how much more advance needs to be made on the nut for a (near) perfect fit is 1/3 of a "flat", then approximately .33x.010 = .0033" needs to be removed from the face.

Chuck the nut up in a lathe and "shave" off the required amount - and you should end up with a "Goldilocks" fit. It may also mean that you need to label each nut for repeatability on future installations.
 
We have an axle jack for our RV-3 which requires a 1” hole to be drilled in the end of the axle nut in order to allow the jack post to fit into the axle. One of the unforeseen benefits of drilling this hole in the axle nut is that you can use long needle nose pliers to guide the cotter pin through the center of the axle and into the bottom cotter pin hole.

Kind of hard to describe, but maybe this picture will help to visualize what I’m saying.

Here is a link to the instruction sheet. It shows how to modify the nut to work with your wheel pants.

https://www.aircraftspruce.com/catalog/pdf/12-00634instruct.pdf

IMG_3309.jpg
 
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HFS said:
Not directly related to the Op's question, but has some bearing on the overall process.

If, when installing the axle nut, the "sweet" spot is not aligned with one of the holes, you can do this -

Since the nut is 16 pitch thread, that means that each round of advancement is equal to .06325" - and each "flat" advancement is equal to .0104" (call it .010).

So, if your estimate of how much more advance needs to be made on the nut for a (near) perfect fit is 1/3 of a "flat", then approximately .33x.010 = .0033" needs to be removed from the face.

Chuck the nut up in a lathe and "shave" off the required amount - and you should end up with a "Goldilocks" fit. It may also mean that you need to label each nut for repeatability on future installations.
Click to expand...

I had an alternate solution...after a few years, for whatever reason, one wheel just wasn't snug when the nut was tightened to align the holes. I dreaded drilling new ones, or trying to remove so much material from the nut that I could get to the next flat, so I used this:

https://www.mcmaster.com/products/peel-away-shims/id~1/

90805a221-@halfx_636843752348640515.png


Worked like a charm.
 
Getting pins through

I struggled with this task many times in the past. After way too many times I decided to grind the end of the cotter pin to a bit of a point. Could not believe how easy it was this time and could believe it took me so long to figure this out.
 
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