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Nose Gear Bolt Failure. Argh!

A $90 bolt vs. a $20 taper pin?

I ordered a taper pin. I'll install it during the condition inspection and never worry about it again.
 
Been following this thread all along and I have to say, it is a very good read! Lots of good comments but I agree with James Clark and RVbuilder that it is just too early to jump to any conslusions. I will leave it up to the factory and those much smarter than me to do their research first. I hope the bolt was saved and gets it's due investigation.

Until then, I will check for any slop in any direction first. I also went back to my construction photos and checked to see if I properly installed the weldment and sure enough, I did. Well that's one thing off the list.

IMG_0066.JPG


Got to thinking if my bolt is long enough to make the threads clear the tube or shear area and found this photo that shows only one washer under the nut. Now I'm wondering if I should take the nut off and see if the shank clears the edge of the hole in the motor mount? Only having about 140 hrs TT so far, I think this will become a check item at the next oil cange or annual.

IMG_8078.JPG


Keep up the good work.
 
If the stop bracket is installed correctly, it shouldn't ever be able to side load the nose gear leg while locking one wheel for a pivot turn, the turn angle of the fork is slightly short of hitting the stop when making a turn pivoting on one wheel.

All,

I just got off the phone with Kahuna who is repairing the aircraft in Florida. He wanted me to pass along that they now confirmed that the WD-631 Nose Stop Flange was indeed installed incorrectly/reversed. Mike also added that the new AN5-20A bolt at the top went in nice and tight.

I've included DWG C1 for those with 'A' models to double check the orientation of the WD-631. This is best shown in Section E-E. If yours is installed backwards, I would highly recommend correction of this before further flight. You may also want to consider changing out the AN5 bolts at the top and the bottom of the gear leg since they would have experienced higher than normal shear loads with this incorrect orientation. (AN5-17A & AN5-20A)

C1.jpg


A couple of thoughts on this from a factory perspective... Aside from the incorrect assembly issue, I've personally watched this same failure happen during the same type of powered tight turning maneuver on another RV-6A (owner bought it used). Fortunately we (several in the group) spotted it early and called for the pilot to shutdown. Thankfully, no prop strike in this case. It's obvious that tight powered turns on the 'A' models produce higher torsional values that could compromise an already worn or weakened bolt. New bolt shear values should have no problems with the load.

What can you do? Personally speaking, I would treat this bolt as a high maintenance/time-life replacement item. What this means to me is that it needs to be re-torqued on a regular basis (perhaps every 50-100 hrs). Depending on your personal use with the aircraft and the type of runways operated from, you might want to replace it with a new one after several Condition Inspections. I look at it as cheap insurance... Again, this is my personal opinion and every aircraft use experience is different.

We get a lot of Tech calls about the gear tube on the engine mount getting wallowed out as the bolt/gear leg combo loosens and wears. This leads to aggravated nose wheel shimmy and then to an eventual expensive repair bill. The repair might include welding the hole shut/match drilling again. So it sounds to me in a lot of cases that this bolt is not getting the attention that it really requires per the number of hours flown. It also varies on what surfaces the aircraft is operated on and pilot experience. Obviously rougher surfaces and less delicate pilots will put more wear and tear on the system. I think the same rule would apply if using a taper-pin or larger diameter bolt. Either way, pay attention to the care and feeding of that 89 cent bolt...
 
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Joe, thank you for coming on here to give your very experienced perspective.

We appreciate it VERY MUCH!
 
Joe, or Scott--------does this issue seem to effect the 10??

Although the nose gear elements are different, the stress generated by tight turns is probably identical or nearly so.

Any suggestions for us 10 folks?
 
Thank you Joe,this is good news.Will the factory consider issuing a SB concerning inspection on condition and time in service?
As Scott pointed out future AP's and IA's will look to the factory for airworthiness directives.Great thread.

To All:I've learned a ton on VAF,Don't forget to make your donation in December to keep this fantastic web site alive and healthy.
RHill
 
try a new AN5 bolt

As a datapoint--

We checked the nose gear on my hangar mate's 17 year-old RV-6A and found the gear to have a visible amount of play. After pulling everything down and removing the original, 17 year-old AN5 bolt, we found it had very slight visible wear. This aircraft has hundreds of landings, many on grass fields.

We installed a new AN5 bolt and the gear is now tight. He will check the gear for wear each condition inspection and replace the bolt at any sign of wear. But we suspect it will be good for many years considering how long the original bolt was in service.
 
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I had a TON of trouble getting the nose gear bolt out at my first annual inspection at 200 hours. It took quite a few hours, some custom tools, some (well, a lot) of cussing. The standard AN bolt was knicked where the very sharp edge of the gear leg had been working against it. I chamfered the hole in the gear leg, and replaced it with a close tolerance AN bolt. I have had no problem with subsequent removals for inspections, which I do about every 400 or 500 hours.

You guy do remove the gear legs for inspections, right??? I remove them, clean them well and inspect with magnification for cracks.
 
I am ordering the bolt Monday. Is a firm commitment to replace the bolt sufficient to keep evil spirits at bay until it's done? :rolleyes:

Would it be possible for you to clean and dye penetrant inspect the removed bolt and post the results? That may help add to the body of knowledge on this issue.
 
Would it be possible for you to clean and dye penetrant inspect the removed bolt and post the results? That may help add to the body of knowledge on this issue.

It's probably doable, however I am still waiting for the replacement NAS bolt to arrive. Hope to complete this work sometime in January and will report back with the findings.
 
SB 14-12-22

Finally started my CI today with a friend and RV builder and found SB 14-12-22 and Mr. Blanks posts very timely. The nose stop flange was reversed. So turned it around and ordered new replacement bolts, washers and nuts including for the engine mount socket attachment. We also replaced the 2 U-611 Disk Spring Washers. N994KS has 851.3 hours on the Hobbs. I'll make this minimally part of the CI.
 
Sorry no crack test

Would it be possible for you to clean and dye penetrant inspect the removed bolt and post the results? That may help add to the body of knowledge on this issue.

Update:
After waiting many weeks for the NAS bolt to arrive my maintenance provider replaced upper and lower nose leg bolts yesterday. They didn't do a detailed inspection of the upper bolt because we discovered in the logbook it had been replaced only last June as part of an unrelated engine mount repair. They didn't believe there was enough time on the bolt for a crack test to be worthwhile.

My suspicion is that the stop plate may have been installed backwards when the nose leg and fork SB was carried out in 2008. If I'm right, the upper bolt survived without incident from mid 2008 to mid 2014 and 200-odd hours.
 
Performed the SB on my 7A with 1100 hrs TT recently. Nose fork stop collar was installed backwards (can't beleive I did that!). The old gear leg to engine mount bolt was in there tight but was easy enough to remove. It was pristine with absolutely no nicks or stress marks. This makes me think that movement in the assembly is as much a factor in bolt failures as a stop collar installed backwards. Installed new bolts and turned the stop collar around to be in compliance with the SB.

Martin Sutter
Building and flying RV's since 1988
 
Update:
After waiting many weeks for the NAS bolt to arrive my maintenance provider replaced upper and lower nose leg bolts yesterday. They didn't do a detailed inspection of the upper bolt because we discovered in the logbook it had been replaced only last June as part of an unrelated engine mount repair. They didn't believe there was enough time on the bolt for a crack test to be worthwhile.

My suspicion is that the stop plate may have been installed backwards when the nose leg and fork SB was carried out in 2008. If I'm right, the upper bolt survived without incident from mid 2008 to mid 2014 and 200-odd hours.

Thanks for the follow-up. It would probably be interesting if others who find the plate installed backwards over longer periods of time could do a DPI and report out on whether they see any signs of incipient cracking.
 
Another data point

We did the SB check on a friends recently purchased RV-6A and found the collar installed backwards.

The gear leg attachment to the motor mount was solid and firm, but in this case the wear point was the hole and bolt in the collar -

collar-2_zps1afaa865.jpg


The softer steel of the collar had distorted and then split under the loading -

collar-1_zps50fbdd77.jpg


In this case it looked like the collar was the weak point.
We don't know the history, but it looks like the bolt was not fully clamping the collar, and the softer collar sleeve wore against the harder bolt each time the turning radius was exceeded.
 
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collar-1_zps50fbdd77.jpg


In this cse it looked like the collar was the weak point.
We don't know the history, but it looks like the bolt was not fully clamping the collar, and the softer collar sleeve wore against the harder bolt each time the turning radius was exceeded.

In a bolted joint like this, the clamping load of the bolt is not what takes the load, and if it was slightly loose, would make a very minimal difference in the over strength of the joint.
It is the shear strength of the bolt being acted upon by the ring and the leg that takes all of the load.
 
In a bolted joint like this, the clamping load of the bolt is not what takes the load, and if it was slightly loose, would make a very minimal difference in the over strength of the joint.
It is the shear strength of the bolt being acted upon by the ring and the leg that takes all of the load.

The bolt held up relatively undamaged but the collar obviously rotated a lot - not clamped down tight? - and elongated the collar hole in a major fashion.

Could this be caused more by tow bar damage rather than "pirouetting" using the brakes and Lycoming for power? Would this put the load on the collar bolt rather than the upper mount bolt?
 
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The bolt held up relatively undamaged but the collar obviously rotated a lot - not clamped down tight? - and elongated the collar hole in a major fashion.

Could this be caused more by tow bar damage rather than "pirouetting" using the brakes and Lycoming for power? Would this put the load on the collar bolt rather than the upper mount bolt?

It could be a combination of any instances that cause the fork to hit the stop, but damage like that is usually the result of a nose wheel shimmy event. The pivot angle during a shimmy event can easily reach the limit of the stop if it is installed backwards.
 
I am currently waiting for my new hardware to arrive to complete the SB. I had Vans throw in a new stop collar as well, and after having a closer look at it (still installed on the plane) today, and now seeing this post, I'm glad I did. My collar shows signs of exactly the same deformation; it appears it has split on both sides above the bolt, just as this one has, and also shows the deformation at the front resulting in space between the front of the leg and the collar.

Yes, my collar is on backwards as well. Having bought my airplane flying, of course, affords me the luxury of being able to blame the builder and absolve myself of any responsibility! Seriously, the guy who built my plane did an exemplary job; if he made this mistake, anyone could.
 
My mechanic son and I attempted to replace the stop collar, mounting hardware, and the gear mounting bolt and associated hardware today, as per the SB. Didn't go very well. First, the bolt holes in the new collar were significantly smaller than the hole through the bottom of the gear leg and smaller than the bolt diameter. Unfortunately I didn't have my drill and bits at the hangar today; didn't think they'd be needed for this job. Wrong. In the process of trying to thread the bolt through the slightly undersized holes, the threads on the new AN5-17A bolt were ruined. Strike 1. Somewhere in there, prior to removing the gear mounting bolt, we tested for play in the mount; there was absolutely none. Good! Removed the gear mounting bolt, which was pristine. Since we were replacing that bolt and nut anyway, we decided we would throw an extra washer on the old gear mounting bolt and use it temporarily in the stop collar. Managed to wreck the threads on that one too. Strike 2. Okay, we knew we wouldn't be able to complete the job today and would have to order a new bolt for the collar, and take the collar home to drill the holes out, but we could put the new gear mount bolt in up top, put the cowlings back on and just come back with the new stop collar bolt and finish the gear reassembly later. Unfortunately, the new AN5-20A bolt would absolutely, positively NOT fit; the shank was too big. We removed the strut and checked the fit of the bolt in the strut hole itself, taking the engine mount out of the equation; would NOT go through that hole. The old bolt was a nice snug fit, the new one simply will not fit; it stops cold at the shoulder of the shank. It might be possible to pound it through, but there is no way to generate any swing in there with the strut in the engine mount, and I believe that the amount of pounding that would be necessary, if it is even possible, would damage either the strut or the bolt. Strike 3 and we're out. Just as a little icing on the cake, by the time we were done messing with all of that, I was no longer sure of the reassembly order for the washers, gear yoke and spring disc. I had tried to keep everything in order as I disassembled the gear, but one extra washer seemed to materialize after disassembly, and I haven't figure out if it goes between the stop collar and the top of the gear yoke, or between the bottom of the yoke and the spring disc (which would mean a washer both above and below the spring disc). The drawing only clearly identifies one washer, so I'm still scratching my head on that one.

So, I have to order a new AN5-17A and drill out the stop collar. No big deal. However, I am a bit puzzled about what to do about the upper gear mount bolt; the new bolt is undamaged and is the correct bolt (I assume), but it flat out doesn't fit. The old bolt, which on visual inspection was in perfect condition, fit perfectly and allowed no play whatsoever in the strut. My fear is I will order another AN5-20A hoping for one with a slightly smaller shank (I know there is some variability in bolt diameter) and the next one won't fit either. I really wish we hadn't wrecked the threads on the old bolt; I would have re-used it and would have been quite confident that it was safe. I guess perhaps I should get a micrometer, measure the old and new bolts, and provide Vans with those measurements when I order a new one; hopefully they can provide a bolt that fits if they have enough information. Any other ideas?

As noted, there seemed to be absolutely no damage done to the upper bolt, hardware, or holes despite the stop collar having been mounted backwards. There was significant damage, however to the stop collar (it looked exactly like the ones in the pictures from az gila above) and the bolt was bent right at the base of the threads. My belief is that the deformation that occurred there absorbed the excess loads from the incorrect collar mounting and may have prevented damage at the top end. Could be wrong, but that's how it looks to me.

At any rate, the plane will be grounded until I can get new bolts (again) that hopefully fit it the prescribed holes. Not a good day at the hangar.
 
<snip>

I guess perhaps I should get a micrometer, measure the old and new bolts, and provide Vans with those measurements when I order a new one; hopefully they can provide a bolt that fits if they have enough information. Any other ideas?

<snip>

Most definitely do this. Measure the diameter of the bolt that fits. That way you will know the true hole size. Personally, I would not drill it out, but get a bolt to fit or ream it with a reamer that has a guide length.

Others more knowledgable about the hardware might be able to guide you on getting a better change of matching the original diameter, once you know it.

I got shivers when you mentioned drilling. The downside is crooked entry and a resulting sloppy hole that no bolt is going to fix.

Your day is sometimes the nature of repairs, it comes with the territory, brush it off and keep going. Nothing was broken.

When I earned a living as a mechanic, there were days I could probably thrust my bare hand in broken glass and come out unscathed, others I could cut myself thrusting my hand in a bucket of ping pong balls. Thankfully the latter was mostly the case.
 
It sounds like you need to get a copy of the plans and construction manual.......

The stop collar (as well as other parts on the airplane) has an under sized hole on one side so that it can be final drilled/reamed for a precise match to the hole in the gear leg. This is done to assure a close tolerance fit between two parts that are drill separately during production. So, if you check the part, the bolt probably goes through one side just fine, but not the other. You are supposed to put it in place and then drill or ream .311 using the larger hole and the hole in the leg to pilot the tool.

As for the bolt not fitting the gear leg, I suspect there is something else going on there that you haven't discovered yet.
AN5 bolts are generally manufactured at the small end of the tolerance range, it would be very strange for the hole to actually be smaller than a brand new AN5 bolt.
 
Thank you for the explanation re: the stop collar.

With regard to the gear mounting bolt, is there a difference in size between the top and bottom holes? I know the bolt is supposed to be mounted with the bolt head on the bottom and the nut on top, but mine was the opposite. Since there was no access to be able to insert the bolt from the bottom, we were attempting to insert it from the top again. We didn't attempt to put the bolt in from the opposite side. Also, I noted that the nut that we removed was not as deep as the new one, so the hardware used may have differed slightly from spec.
 
Thank you for the explanation re: the stop collar.

With regard to the gear mounting bolt, is there a difference in size between the top and bottom holes?

The diam. of the hole should be the same through the entire assembly.
Proper installation of the bolt will result in the bolt shank protruding through the opposite side, requiring 1 or 2 washers under the nut to account for the protruding shank.
 
Measured the old and new bolts tonight: Both old bolts measured .309, both new bolts measured .310. Inside diameter of the hole through the gear leg measured between .309 and .310 (digital calliper only reads to thousandths). Interesting. I think I'll order half a dozen AN5-20A's to increase the odds of getting one that will fit well.

Bit of a dilemma regarding mounting orientation and use of washers. Original installation had the bolt mounted head up, with a washer under the head and one under the nut. Experimenting tonight with the old bolt, use of a washer under the bolt head appears to keep the bolt shank from extending far enough out. However, without a washer the end of the bolt hits the firewall and (without being tightened down) the head is very slightly shy of touching the top of the tube. Hmm. The original nut installed is not the one specified; it is an unusual locknut which is significantly shorter than the spec piece, I assume to provide a bit more clearance from the firewall. Obviously the builder struggled with these issues during construction as well. Although some of his choices would not, according to what I have learned from this thread, be considered optimal, the bolt and holes appeared to have no significant wear, despite these compromises and incorrect orientation of the stop collar.

Installing the bolt as recommended, with the bolt head down and the nut on top, would require an access panel which is not there and would be very difficult to cut without removing the engine and mount, so this does not appear to be a viable option at this point.
 
Installing the bolt as recommended, with the bolt head down and the nut on top, would require an access panel which is not there and would be very difficult to cut without removing the engine and mount, so this does not appear to be a viable option at this point.

I already suggested that you get a copy of the plans.
If you did that you would see that there is no access panel.
All that is required to install the bolt in the recommended orientation is a properly located 3/4 " hole to pass the bolt through. Once the bolt is installed, the hole is closed off with a 3/4 stainless steel hole plug.

The hole can be made working from the aft side.
 
The recommended orientation of the gear mounting bolt (head down, nut up) was done opposite head up nut down in my 6A.. Other than following the plans, is there any reason it shouldn't be done this way? I can't find on the plans where it actually shows this. The bolt call out is on page 75 and a drawing there looks like the orientation is head up, but isn't clear.
Waiting for NAS bolt install.
Sheldon
 
The recommended orientation of the gear mounting bolt (head down, nut up) was done opposite head up nut down in my 6A.. Other than following the plans, is there any reason it shouldn't be done this way? I can't find on the plans where it actually shows this. The bolt call out is on page 75 and a drawing there looks like the orientation is head up, but isn't clear.
Waiting for NAS bolt install.
Sheldon

I haven't checked to confirm, but I believe a plans revision was made long ago, to show the bolt installed with the head at the bottom.
 
I haven't checked to confirm, but I believe a plans revision was made long ago, to show the bolt installed with the head at the bottom.

Plans showed head up when I built my RV-6A but I put head down and nut on top due to lack of clearance for the nut to be on the bottom.
 
I haven't checked to confirm, but I believe a plans revision was made long ago, to show the bolt installed with the head at the bottom.

Yes, and IIRC that was the same revision that added the 3/4 access hole.

The RV-6 could have been built exactly to the then-current plans with no firewall hole and the bolt head up...
 
From Fred Stucklen in a related thread

"If the nut is impossible to get started onto the bolt, use a 1? rounded dowel and a hammer to indent the firewall so you are able to get the nut started. "

This is my plan for when I get to this task on the -6A this spring. It's been 18 years but I remember the access issue without the plans revision.
 
I built my 6A per plans, bolt head up. I use a metal lock nut (the smaller hex type - don't have the AN designator handy). I need to put the bolt partially in, start the washer(s) and nut, then advance the bolt as the nut is tightened. No dent needed in the firewall.
 
I built my 6A per plans, bolt head up. I use a metal lock nut (the smaller hex type - don't have the AN designator handy). I need to put the bolt partially in, start the washer(s) and nut, then advance the bolt as the nut is tightened. No dent needed in the firewall.

Alex... You are a very smart grasshopper!! :D
 
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