Broken Tail wheel bolt

[Darrel Starr]

Steve, I can see why you use hard washers -- actually seems like a good idea especially if the tailwheel is going to get some (a few) shock loads around the yield strength. But if someone out there puts a washer under the head, make sure it clears the radius on the head.

I just talked to Wup, appreciate his offer to take these parts back. I will package up mine & Randy's.

I have ordered some AN8-21 bolts. After 35 years at Caterpillar where the smallest bolt is 3/8 diameter, I feel qualified to overdesign this sucker!

[12 Geezer]

Steve mentioned cupping of the washer, hence using the grade 8 washer which is probably somewhat thicker. And if I'm not mistaken, it seems Caterpillar washers are an even thicker pattern than standard grade 8. Sounds like just the ticket to me - - always liked Cat hardware. Though Darrel, I think you may be mistaken about that 3/8 minimum bolt size - there are some mere 1/4" bolts on my D-8H. I think they hold on some placards.

[Darrel Starr]

Geezer, now that you mention it, 3/8 bolts for placards is a little overkill.

You are right about CAT. CAT uses all Grade 8 hardware even to hold placards on. And the washers are unusually thick and bullet proof. These would be the ultimate no nonsense washers for the tail wheel. I am waiting for Bill Rusk to wonder about the weight being added though.

[behindpropellers]

Considering these bolts were given away for free with membership renewal....

Why not keep the bolts until the tests are done and then find out what the fix for the problem is and then just get an exchange.

I hate to see AKBW eat $40 a pop for something they gave away for free or cost.

Tim

[Darrel Starr]

Free? I paid $40 + $5 shipping for mine.

[mike mcs repair]

Free? I paid $40 + $5 shipping for mine.

same here, well my customer did....

[Darrel Starr]

I called Wup yesterday, he generously gave me a Return Authorization # so my eye bolt & Randy's are on their way back to Oregon. Good people, but this was a defective product they are standing behind.

[12 Geezer]

Checked mine to day before flying - it was loose - approx 60 hrs since installation. Not rattling loose, but what one might describe as "barely snug". AN7 bolt with AN washer and AN elastic stop nut, originally tightened "pretty darn tight", but without a torque wrench. Sounds like this is definitely a maintenance item. Like maybe re-tighten with every oil change.

Tip of the hat to ABW for their proactive approach to this.

[phdigger123]

This weekend I replaced the tailwheel bolt and the bolt holding the spring to the fuselage. The tailwheel bolt was snug, not tight, and showed some wear. This will be something that I will be keeping a close eye on in the future.

[barbwire]

IMG_0110.JPGIMG_0109.jpg

I hope you can see in the pictures that the rubber ripped and left the spring loose.

I had been following this thread and decided to have a close look at everything last night.
My last 35 plus landings have been into some short rough fields.
After looking the situation over I decided to replace the rubber with belting material.
Also replaced the bolts with grade 8's.
55 hours on this setup since new.
Everything else looked tight.------ Thanks for all the useful information. I plan to replace all the bolts next annual.

[dougsappllc]

Barbwire,
If you look at the close up photo MG_0110.JPG (http://www.supercub.org/forum/attach...4)IMG_0109.jpg (http://www.supercub.org/forum/attach...1&d=1343166644) reeeeeeeeel close you can actually see a space between the head and the washer which is under the head. I think something may be wrong, if it were tight and everything square and in line the head of the bolt should be down tight on the washer all the way around. Because you say it's tight and the space is plain to see I think that the bolt is not square with the bracket and is placing all the load on the forward half of the bolt head. Might be worth looking at.

[Aviator]

Changed my T/W bolt today. Here's what came out after 60 Hrs and about 100 T/O-Landings since new.

TW_bolt.jpg

Not visible on this pic, but there appears to be definite motion and shearing on the bolt between the 1st and the 2nd spring leaf.

TW_bolt_Dwg.jpg

[8GCBC]

Looks fine to me.

[Longwinglover]

Just turn it 180* and it will straighten back out. Good as new!

John Scott

[Aviator]

Question...
The L-21 E&M Manual p. 50 says torque to 20 but not more than 35 foot-pounds. The use of AN310 (castle) nuts suggests the designer anticipated relative movement of the clamped parts. The parts catalog calls for a bushing (751 350, #3241-2) and a spacer (752 888, #3243-2) through the spring leaves. I suppose it's there to take the torque without clamping the two leaves together. Trouble is the holes in the springs are 7/16. Is anyone using springs with bigger holes (other than Pawnee springs)?

[jgerard]

Question...
The L-21 E&M Manual p. 50 says torque to 20 but not more than 35 foot-pounds. The use of AN310 (castle) nuts suggests the designer anticipated relative movement of the clamped parts. The parts catalog calls for a bushing (751 350, #3241-2) and a spacer (752 888, #3243-2) through the spring leaves. I suppose it's there to take the torque without clamping the two leaves together. Trouble is the holes in the springs are 7/16. Is anyone using springs with bigger holes (other than Pawnee springs)?

The bushing and spacer are in the tail wheel head not the springs. The bushing takes you from a 1/2" to 7/16 bolt hole and the spacer takes you from a 1-3/4 wide to 1-1/4 wide leaf spring. If you put the Pawnee springs on you do not use those items.

I have allways used castle nuts on both the front spring to fuse and rear tail wheel to spring bolts. In my experiance nylock nuts allways get loose. Tail wheels and tail wheel springs are notoriously overlooked during annuals. Hopefully this tread causes pilots to take a look at their aircraft.


Jason

[Bill Rusk]

If you use castle nuts don't forget the cotter pin.

Bill

[Aviator]

The bushing and spacer are in the tail wheel head not the springs. The bushing takes you from a 1/2" to 7/16 bolt hole and the spacer takes you from a 1-3/4 wide to 1-1/4 wide leaf spring. If you put the Pawnee springs on you do not use those items.

I have allways used castle nuts on both the front spring to fuse and rear tail wheel to spring bolts. In my experiance nylock nuts allways get loose. Tail wheels and tail wheel springs are notoriously overlooked during annuals. Hopefully this tread causes pilots to take a look at their aircraft.


Jason

Thanks, Jason. Sounds like changing this bolt every 100hrs is the best option.

[Darrel Starr]

Sent the eye bolt back just before Oshkosh - a $40 check was waiting for me when I got home. Exceeded my expectations!

[Steve Pierce]

IMG_0110.JPGIMG_0109.jpg

I hope you can see in the pictures that the rubber ripped and left the spring loose.

I had been following this thread and decided to have a close look at everything last night.
My last 35 plus landings have been into some short rough fields.
After looking the situation over I decided to replace the rubber with belting material.
Also replaced the bolts with grade 8's.
55 hours on this setup since new.
Everything else looked tight.------ Thanks for all the useful information. I plan to replace all the bolts next annual.

Grade 8 bolts are harder and will break where an AN bolt will bend. I would rather have a bent bolt stay in place than a broken bolt fall off. Just something to consider.

[supercub24a]

Just clicked on this thread today was wondering why this is staying up so long ?? well guess after reading using ms bolts with the cupped washers & nut. I have never had tailwheel bolts break ! castings and springs never bolts i just kring! when i see citabra's and scouts axle bolts held on in a ski installation with AN bolts with solid axles but it is cheaper! i'm sure that eye bolt is not made for tension loads thats my two cents.
Steve C

[barbwire]

Thanks Steve, I will change them out.
As a side note, the belting is working great as a cushion and should be a long lasting fix.

[Bill Ingerson]

Just checked my tail wheel again after about 8 hours on flying it after tightening the Eye bolt. It was really loose this time, sloppy loose, had masive tail shimmy when landing. This time I will take the eye bolt out and put in a AN7-21 bolt with hardened washer like Steve said to do. I really like the idea of the eye bolt but can no longer take a chance on it breaking. Hope BushWheels can find out what is going on there. There a good company that just ran into something no one was aware of.

[Steve Pierce]

How tight did you tighten the eye bolt? Was the shimmy caused by a loose bolt or vice versa. Have not heard of the bolt getting loose, just the ones that broke.

[n40ff]

I'd take a close look at holes in springs. Just shortened the spring on my homebuilt to lower tail and noticed that the oval/overlaping holes on the two leafs had not been machined out completely and did not offer complete clearance for relative motion, therefore putting shear force on bolt. BTW, I found springs relatively tough but not too hard to drill if proper speed/feed and cutting oil was used...

[nanook]

What exactly is coming loose? Are you using a good high temp self-locking nut?

[Bill Ingerson]

This would be four or five times now that I have had to re-tighten the eye bolt. The eye bolt has a washer and nylon nut to tighten it down with. I have been using the same nut each time I tighten it. I have tried different torque settings for this nut from 30 to 50 pnds. Doe's not seem to matter.
I can always tell when its getting loose by the tail shimmy. When someone is in back its worse. I have the new tail spring bush wheel came out with for the baby bush wheel. Had a hard gust from the side a weak brake on the right and a loose tail wheel when landing and that combination caused me to do a interesting slow ground loop. New brakes are ordered, Eye bolt coming out and I will try to stay ahead of the plane next time.
I will look closer at the spring and always use a new nut.

[Steve Pierce]

I wouldn't blame the eye bolt for getting loose, I think you have a nut that has lost it's locking feature. I would get a new AN363-720 nut with a AN7-22A bolt and a grade 8 washer and torque it to 50 ft lbs.

[tophand]

I'm replacing mine when the parts get here. I was checking over my plane the other day and the tail wheel looked funny. I grabbed the tail post and wobbled the tail wheel back and forth on the spring. That was an oh @#$% moment. It ruined the spacer for the J3 spring. While I was ordering new parts I was talking to Wup and he told me the eyes are supposed to be torqued to 60fp. I think mine would have broken eventually with that much slack. They also are going to hold off on selling any more till they get this ironed out.

.....Mike

[Steve Pierce]

I find these things loose all the time with AN bolts. I think the original concern with the eye bolt was breaking which tells me it could be hard. Now people have them getting loose. I will be interested in hearing people's experience with the AN bolt.

[SuperCub MD]

Could we extend the "shoe" (mating surface) up the spring a little more and use (2) bolts? I.e. manufacture the TW "shoe" a couple of "inchs" longer, giving enough room for a second bolt?

Yes, that is the answer, and it was done a long time ago. The later PA25's used the 2 hole Scott with 2 hole springs. I had Bushwheels build me one some years ago and run it with 3 PA25 2 hole springs (instead of 4, one helper removed). It has been bullet proof so far, I don't know why more people don't run them. No more loose or broken bolts.

If you have a 1 hole replace that bolt regularly no matter what type it is. I used to tighten everything back there once a month and replace all the attach bolts every year when I was flying the cub a lot.

[Steve Pierce]

I can't believe you added the weight of an extra bolt but I guess you had an extra hole drilled too.

Cub Crafters uses the two bolt on their Type Certified Top Cub as well. SJ has one. If he hasn't broken it yet it must be tough cause he is hard on stuff.

[Darrel Starr]

My advice -- remove all of these defective eye bolts!!!!!!

[SuperCub MD]

I can't believe you added the weight of an extra bolt but I guess you had an extra hole drilled too.

Cub Crafters uses the two bolt on their Type Certified Top Cub as well. SJ has one. If he hasn't broken it yet it must be tough cause he is hard on stuff.

I DID deliberate the weight of the bolt long and hard, but figured with it way out back I could brake a little harder.... I didn't know it was on the top cubs, thought I had something unique. I may have had a picture of my wheel in a Cub Clues, don't remember, it's been a long time.

And I'll add....Having used the 2 hole a while after the 1, I would buy the casting and springs to convert any 3200 I ran on a Cub this way, It's a huge improvement.

[Aviator]

I had a look at a Bird Dog today. Its 3200 tailwheel is attached to the master spring leaf only, but with an MS20007 bolt which also holds the glider tow release.

As far as load carrying is concerned, all the last 2-3 inches of the 2nd leaf of on SC does is upset the progressive and gradual load pick up laminated springs are designed to do. If it's clamped to the tailwheel just as a backup in case the master leaf fails, then there's no reason for it to slide on top of the master. And an MS20007 bolt can be preloaded with a much higher torque than an AN7 to really clamp everything together real tight.

[hottshot]

Ok here are the results from the testing lab,

Please notice that the bolts have broken in the threaded portion of the bolt, which is where they are typically supposed to break. They all rested right at 100,000psi.

Per the manufacture, failures of the type you described have always been attributed torsional over-load.
Below is the actual response from the manufacture:

"It has been our experience that with field-failures of the nature that you are describing, they have always been attributable to torsional over-loading of the product, meaning that the product was over-torqued, or tightened-down too hard, during installation. It is our recommendation that the product only be installed “hand-tight with a wrench”, to eliminate the stresses that are introduced when the product is torsionally overloaded".

Results:

Serial# Width Dia. or Gauge
Area Yield (lbs) Ultimate (lbs) Ultimate(psi)
I 7/16-20 .1288 12,791 99,300
2 7/16-20 .1288 12,771 99,200
3 7/16-20 .1288 12,998 100,900


ABI-EB-0716-721 TEST 3.jpg


Now on to the testing we have done here... In order to figure this out we have been eyeballing this for hours and this is what we have come up with.

The point of failure has had us really questioning things
point of failure.jpg

So we have gone through the installation a few times and this is what we are seeing.

When you install the bolt in a 3216 head on a standard cub spring or other wise you will need to install with a 3243-3S spacer to take up the 1/2" hole in the head to make it a 7/16" we noticed on the broken bolts that the radius area of the bolt was shiny and worn, and you guessed it the 3S Spacer stops there and didn't make a flush contact with the head..

3scontact.jpg

We then installed a washer on the bolt (like it should be under the head) and then installed the 3S Spacer to see the head have a full contact on the load bearing surface

fullcontact.jpg

Now also as noted in several conversations previously on S Cub .org the 3S Spacer protrudes through the head bracket of the tail wheel and into the spring, most times we see this part smashed and out of round because it don't really fit into the spring with a 7/16 hole. ** Note we didn't invent any of this we just PMA'd the parts so we all could get them when we need to.

3sin3216.jpg


So We still will offer the $40 return for those that would like to return the bolt. At this time we will not be selling any of the Eye Bolts and in the future but will be changing out PA-18 Tail spring to a 1/2" attach hole to delete the use of the 3S Spacer in future installations.

[Steve Pierce]

Wup, Thanks for the information. I turn the 3S spacer down when not using the 1 1/2" or 1 1/4" sping adapter. I can see where just smashing that thing in there it would cause a problem.

[Tim]

Thanks Wup for the work on this

[Bill Ingerson]

Talked with Wup today and I am going to keep my eye bolt on. The new tail spring they sell has a better arch to it and the sleeve that goes in the bolt hole through the springs may need to be machined down flush with the springs and a washer installed as instructed. You still need to check them them every 15 or 20 hours for being loose, just part of your preflight. Thanks BushWheels for giving us your attention on this.

[Darrel Starr]

Wup, are you now recommending a 1/2 inch diameter bolt (AN8-21)? What torque would you recommend (Standard AN8 torque of 40 - 58 lb-ft?). Would you use an elastic stop nut or a castellated nut? Do you recommend "hand tight with a wrench" as stated above? That is opposite to the recommendation by Gilbert Pierce who recommended to tighten the bolt to be just below yield. Your original recommendation with the eye bolt was 40 or 50 lb-ft as I recall and the use of an elastic stop nut so the full torque would not be backed off to match a cotter hole.

Should we follow the advice you gave Maule owners?
Maule Eye Bolt.jpg