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Rear eyelets chewing through bolts with rack installed

Old 07-23-20, 10:02 PM
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Rear eyelets chewing through bolts with rack installed

Sorry for the long post.

I recently found that the rear rack bolts I used (M5 x 35mm Stainless Steel A2-70 grade) were bent. I purchased a newer bike and wanted to transfer the rack over, and while trying to remove the rack both SS bolts were VERY hard to remove…almost as if they were seized. I was able to remove one bolt with a lot of resistance and noticed how bent it was when it was removed. The other bolt wouldn’t spin after about ¾ of the bolt was out, and then the bolt head broke/spun off. Fortunately, there was enough thread remaining where I could get pliers on it and spin it out.

Not thinking it all the way through, I went out and purchased two more M5 x 35mm SS bolts to mount the rack on the newer bike (both older and newer bikes are Cannondales with rear eyelets). Mounted the rack (inside of the eyelet) and rear fender (on the outside of the eyelet). The install was straightforward and I tightened everything up. When I went to check to see if the bolts were able to be loosened, the same thing happened – they were stuck…and even before I put any load on the rack! This time both bolts could not be loosened and both sheered off. I had to drill both bolts out. Parts of both eyelet threads were drilled/damaged, but enough good ones remain for me to still thread new bolts through and hold. I’ve also been using a nut on the other side of each bolt for additional tightness.

So now we’re here: I’m trying to do my due diligence in researching bolt grades because lesson learned…I’m not going to use any more SS bolts. I’ve purchased two M5 x 30mm 10.9 grade bolts, but have not installed them. My fear right now is although 10.9 grade is stronger than the SS A2-70 grade bolts I’ve been using, will these also get stuck in the eyelets? The rack is a Burley Moose rack used to pull my daughter’s trailer bike and to hold my panniers for light-medium duty grocery loads. I also see that there are 12.9 grade bolts as well….but none in the M5 x 30/35mm length. I’m not really quite 100% sure why the bolts are getting stuck in the eyelets to begin with. I mean I have an idea, but just a bit perplexed. And if the 10.9 bolts get stuck, I’m assuming they’ll be even more challenging to drill out due to them being harder?

Sorry for the long first post, but I’m seeking any feedback or advice on what to do to ensure that the rack is safely installed as it's towing precious cargo! And I would like to not have to deal with stuck/broken bolts that need drilling out again!
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Old 07-23-20, 10:14 PM
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Originally Posted by Hank3
while trying to remove the rack both SS bolts were VERY hard to remove…almost as if they were seized. I was able to remove one bolt with a lot of resistance and noticed how bent it was when it was removed. The other bolt wouldn’t spin after about ¾ of the bolt was out, and then the bolt head broke/spun off. Fortunately, there was enough thread remaining where I could get pliers on it and spin it out.

Not thinking it all the way through, I went out and purchased two more M5 x 35mm SS bolts to mount the rack on the newer bike (both older and newer bikes are Cannondales with rear eyelets). Mounted the rack (inside of the eyelet) and rear fender (on the outside of the eyelet). The install was straightforward and I tightened everything up. When I went to check to see if the bolts were able to be loosened, the same thing happened – they were stuck…and even before I put any load on the rack! This time both bolts could not be loosened and both sheered off. I had to drill both bolts out.
This sounds like a classic case of galling, which happens with SS nuts and SS bolts. Or Ti nuts and Ti bolts. Galling is when similar metals cold weld to themselves under high friction. What material is the frame/eyelet?

Originally Posted by Hank3
Parts of both eyelet threads were drilled/damaged, but enough good ones remain for me to still thread new bolts through and hold. I’ve also been using a nut on the other side of each bolt for additional tightness.
There may be enough threads, and the nut (I'd use a nylock nut) is a good idea. If the eyelets are safety duty (it sounds like so) you may want to have a safety chain from your seat post to any trailer or trailing bike and not depend entirely on the eyelets.

Originally Posted by Hank3
So now we’re here: I’m trying to do my due diligence in researching bolt grades because lesson learned…I’m not going to use any more SS bolts. I’ve purchased two M5 x 30mm 10.9 grade bolts, but have not installed them. My fear right now is although 10.9 grade is stronger than the SS A2-70 grade bolts I’ve been using, will these also get stuck in the eyelets? The rack is a Burley Moose rack used to pull my daughter’s trailer bike and to hold my panniers for light-medium duty grocery loads. I also see that there are 12.9 grade bolts as well….but none in the M5 x 30/35mm length. I’m not really quite 100% sure why the bolts are getting stuck in the eyelets to begin with. I mean I have an idea, but just a bit perplexed. And if the 10.9 bolts get stuck, I’m assuming they’ll be even more challenging to drill out due to them being harder?
If the problem is galling, using regular high strength steel bolts should improve that. I'm confused, though: you are using M5 bolts that are over an inch long? I can't figure out where you'd use a 35mm screw. Is this your rack?


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Old 07-23-20, 11:20 PM
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Originally Posted by WizardOfBoz
This sounds like a classic case of galling, which happens with SS nuts and SS bolts. Or Ti nuts and Ti bolts. Galling is when similar metals cold weld to themselves under high friction. What material is the frame/eyelet?


There may be enough threads, and the nut (I'd use a nylock nut) is a good idea. If the eyelets are safety duty (it sounds like so) you may want to have a safety chain from your seat post to any trailer or trailing bike and not depend entirely on the eyelets.


If the problem is galling, using regular high strength steel bolts should improve that. I'm confused, though: you are using M5 bolts that are over an inch long? I can't figure out where you'd use a 35mm screw. Is this your rack?


https://www.youtube.com/watch?v=S8rWrvrJnaw

Hi WOB - Thank you for chiming in. I felt elation after reading your response. I have never heard of "galling" before but it sure seems like a perfectly logical explanation of what I've been experiencing! The bike frame is what Cannondale calls a "SmartForm C2 Alloy." Not 100% what all that means other than it's light and maybe stronger? And I'm assuming that's the same material in the eyelets. The YouTube video is the rack that I have - Burley Moose Rack. The reason why the bolt is as long as it is is because the eyelet hole is relatively wide, and I'm also securing a rear fender and the rack. Furthermore, I'm adding a couple washers and then enough male thread on the other side to secure a nut.


I looked up galling prior to replying here and it looks like nylon lock nuts are a very common cause for galling with SS bolts. I didn't use nylon lock nuts on my previous bike (also a Cannondale but the frame was "Aluminum Alloy"...which is probably similar to the "SmartForm C2), but I did use SS nuts so galling was probably the issue there as well. The bending from the SS bolts probably was due to load from the rack I'm assuming.


So do you think using 10.9 grade bolts this time should reduce the chance of galling? And using the SS nylon lock nut should be ok with the 10.9 bolts (or another type)? The SS washers I've been using OK as well? Or should I try to source 12.9 grade bolts? I also thought about 8.8 grade as well which is not as strong though. Also read in the galling article that using some type of lubricant would help reduce galling but not sure if that comes into play if I'm not using SS bolts this time.



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Old 07-24-20, 05:12 AM
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If you didn't clean up the threads when the first set got chewed up it is understandable that the second set suffered the same fate.

I always put a thin coat of grease on any threads like that for just the reason you experienced. Although in your case I think the threads were destroyed when you tried removing a bolt that was bent from the load bearing down on it.

If you are running a nut on the other end (nylon lock nut would be ideal) than I would consider reaming out the threads in the frame eyelet and switching to a bolt that is only threaded on the end. If you really want to go mad dog than consider an AN3 bolt. Strongest stuff made, even come in stainless. A 10-32 has a shank that is 3/16 inch (4.76 mm). Get one with a grip that puts the threaded portion just inside the width of your attachments and you are good to go.

https://www.aircraftspruce.com/catal...es/anbolts.php

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Old 07-24-20, 06:37 AM
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Sounds like a combination of galvanic corrosion and perhaps a bent bolt that now has bent the frame as well.
Stainless steel is very strong but it does 'work harden'. Meaning it will become hard and brittle when drilled or bent.

My first instinct would be to tap out the hole so it is at least straight again, maybe in a larger diameter so you can retap it.
Then always use lube to install bolts. You will thank yourself a couple of years down the road.

Also, if the insides are tapped, why not use two shorter bolts? Less risk of this happening or them bending and getting stuck. That's an awful lot of bolt to use.
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Old 07-24-20, 07:10 AM
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Stainless can gall with aluminum if the fit was too tight and especially if the materials (like the SS) was of poor quality (e.g. Home Despot).

Not sure if corrosion was the cause of the initial cold-welding, but if you ran the bike without racks for any length of time (or if water got into the SS/frame area consistently) then the corrosion could have caused the hole to shrink, placing a lot of force on the bolt/frame surface, encouraging galling.

Steel screws have (much) less a chance of galling. The 10.9 or 12.9 bolts should both be way stronger than nondescript SS bolts. If it were me, I'd

1) Run what is called a form tap (which squashes the threads into place without removing metal) through the hole WITH THE RECOMMENDED LUBRICATION to restore threads as best I could. This is optional. I'd think twice before running a cutting tap through the hole. You want an M5 FORM TAP. A thead chasing tap also would cut away additional material. I'd be tempted to avoid removing any more material. The point of this step is to make sure that the threaded hole is properly large enough.

2) Use some anti-seize (this is overkill if you are using steel bolts, for which some grease would suffice) on the bolt threads and in the bolt hole.

3) Tighten the bolt. If you have enough thread left, torque the bolt to proper torque.

4) Use a nylock or other locking nut on the inside end, and torque it as well. You could also use a regular nut, with threadlocker (blue/medium/removable).

Given the length of the threaded part of the frame, I don't think you should have strength issues especially with the nut you've added. The bolt is loaded in shear and the stress is not on the threads, its on the bushing (probably why its so long) and the nut head.

Good luck.

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Old 07-24-20, 07:57 AM
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Appreciate all of the feedback and info everyone. This has definitely been a humbling learning lesson. Of course I wish I would've known all of this prior to avoid all of the work and hassle...and not to mention the countless trips to Ace, Lowe's, and HD.

I have considered just enlarging the eyelet by reaming out the threads. I saw some 12.9 grade M5 x 30mm allen bolts at Ace Hardware, but it was half threaded so it wouldn't fit completely through the hole. But if I enlarged it slightly, then it should work. If I opt not to use washers, I may be able to go wit a 25mm size, but with the frame eyelet being as wide as it is, I don't think going any shorter would provide enough threads to use a nut on the other end. To me, there still seems to be enough good threads remaining. I have a M5 cutting tap on hand, but not a form tap. As far as lubricants, I have these on hand:
  • Gray Permatex Anti-Seize
  • Multi-Purpose White Grease
  • Multi-Purpose Synthetic Grease
  • Park Tool Blue Polylube Grease
Can I reuse the nylon lock nuts that I just removed or getting a new ones be better? Also, would putting loctite and a type of lubricant on the same bolt somehow counteract one another?
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Old 07-24-20, 09:04 AM
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.


Through bolting is not uncommonly used to repair failures when aluminum alloy threads give up under use. And you gain the advantage of not needing to worry any more about the seizing business.

But check your clearance on the drive side to make certain you can do this without cog or chain interference by the bolt/nut.
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Old 07-24-20, 09:21 AM
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Originally Posted by 3alarmer
.


Through bolting is not uncommonly used to repair failures when aluminum alloy threads give up under use. And you gain the advantage of not needing to worry any more about the seizing business.

But check your clearance on the drive side to make certain you can do this without cog or chain interference by the bolt/nut.
Clearance shouldn't be an issue, but I appreciate you bringing that up for my awareness. "Through bolting" is definitely something I'm considering at this point. I just hope that if I choose to go this route, that the eyelet's structural integrity won't be compromised by drilling out the threads and making the hole slightly larger. And then the question will be to remain with a M5 or move up to M6. But I think I would go up to a 12.9 grade bolt at that point...might as well.
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Old 07-24-20, 09:54 AM
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Stainless thread galling can be prevented/reduced by a light film of anti-sieze.
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Old 07-24-20, 11:14 AM
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Putting the nut on the end of the bolt may be a part of your issue. When you torque the nut you are partially unloading the tension of the bolt on the threads of the eyelet. I believe that this may lead to the bolt moving around inside of the eyelet threads where it may not have, if torqued against the eyelet normally. If you need a nut on the end I believe that the suggestions to drill out the eyelet threads may be sound advice.
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Old 07-24-20, 01:32 PM
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Any reason not to have the rack leg and the fender brace on the same side of the dropout? That way you don't need the nut.




Cheers
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Old 07-24-20, 01:39 PM
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Originally Posted by Miele Man
Any reason not to have the rack leg and the fender brace on the same side of the dropout? That way you don't need the nut.

Cheers
Only reason the rack legs are on the inside right now is due to the width of the seat stays. Burley didn't design the rack for bikes equipped with disc brakes and when I asked them about the rack being fitted for disc brake setup ups, they basically said I could bend them out but it would be at my own risk in order to avoid liability. I did consider that in the beginning but for whatever reason opted to go on the inside. Probably because I figured it was one less thing to do.

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Old 07-25-20, 10:12 AM
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Bending rack arms

If you bend the rack arms in order to move them to the outside, they may end up asymmetrical, so the rack isn't entirely straight. I bent the arms on a non- disc Ibera rack out and was extremely careful, but the rack is still a bit off from straight. Not a big deal, but be as careful as you can to try and bend each arm the same amount. Good luck.
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Old 07-25-20, 11:22 AM
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Originally Posted by Chuckles1
If you bend the rack arms in order to move them to the outside, they may end up asymmetrical, so the rack isn't entirely straight. I bent the arms on a non- disc Ibera rack out and was extremely careful, but the rack is still a bit off from straight. Not a big deal, but be as careful as you can to try and bend each arm the same amount. Good luck.
Appreciate the insight. The arms are pretty beefy and would take a good bit of force to bend out, which was one of the reasons I was uninspired to go that route
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Old 07-25-20, 01:48 PM
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If you go with the AN3 bolt you won't need to drill anything out. A 3/16 shank should fit inside the M5 threads. Of course the threads won't live long if you do, but sounds like they are toast anyway.
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Old 07-25-20, 03:44 PM
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I have bought 8.8 5mm bolts, in 8mm hex head, & not stainless but paint the heads once they're in..

a tapered tap can chase the damaged threads..
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Old 07-27-20, 08:05 PM
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Had to wait for new rack stays to come in to install the rack back on with the new hardware arrangement. Since my previous bike was a "L" frame, the previous stays didn't work on the new "M" frame. Install was very straightforward as expected with the holes smoothed out. The 12.9 grade bolts seem stout and strong and I opted to go with nylon lock nuts. Went for a brief ride with my daughter this evening and all seemed OK. Will for a grocery run with tomorrow night and see how things hold up. One thing I know though: The bolts won't be seized on the eyelets next time around!

Thank you to everyone who did a great job of informing and enlightening me and saving me the chagrin of my previous mishap. I have learned a good bit of new info that will serve me well in the future.









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Old 07-27-20, 08:33 PM
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Ah missing data provided by photos. The Op has a rack mounted child ride along device (looks to be a Burley Piccolo, or a copy of. These child "tag a long" devices place a serious amount of lateral force on the rack, hence a lot on the rack's mounting hardware. I note that the rack's structure has minimal triangulation to resist the lateral forces. I sold and service Burley products for quite a few years back in the late 1980s and early 1990s and seem to remember that Burley didn't want the mounting bolts doing double duty. rack and fender mounting.

A previous poster asked about why not just tandeming the rack and fender braces on the same side of the drop out eye. The obvious answer is to minimize the bending forces. rack bolts like shear but not bending forces. Andy
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Old 07-27-20, 08:43 PM
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Originally Posted by Andrew R Stewart
Ah missing data provided by photos. The Op has a rack mounted child ride along device (looks to be a Burley Piccolo, or a copy of. These child "tag a long" devices place a serious amount of lateral force on the rack, hence a lot on the rack's mounting hardware. I note that the rack's structure has minimal triangulation to resist the lateral forces. I sold and service Burley products for quite a few years back in the late 1980s and early 1990s and seem to remember that Burley didn't want the mounting bolts doing double duty. rack and fender mounting.

A previous poster asked about why not just tandeming the rack and fender braces on the same side of the drop out eye. The obvious answer is to minimize the bending forces. rack bolts like shear but not bending forces. Andy
You're right, Andy. I know there's a good bit of force going on the rack from the Piccolo. I tried a trailer cycle that attached to the seatpost but my daughter felt very uncomfortable with that setup...as well me since it rocked my bike side to side more aggressively. I'm sure I could get used to it over time, but the Burley seemed like a better choice for us.
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Old 07-27-20, 09:03 PM
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Very nice, clean install.
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Old 07-28-20, 04:36 AM
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Never seen a fifth wheel bike trailer.

A two headed bike as my daughter called ours. The child will outgrown that trail a bike in the blink of an eye. Enjoy it while you got it.
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Old 07-28-20, 08:20 AM
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Originally Posted by Andrew R Stewart
I note that the rack's structure has minimal triangulation to resist the lateral forces.
Andy, would you recommend that the rack stays be outboard, and the fender wires be inboard, to give a bit wider stance and resistance to lateral force?
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Old 07-28-20, 08:41 AM
  #24  
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Originally Posted by Pop N Wood
Never seen a fifth wheel bike trailer.

A two headed bike as my daughter called ours. The child will outgrown that trail a bike in the blink of an eye. Enjoy it while you got it.
You know it too well! My daughter has been riding with me since she was a year old (she's now 5.5), and I was fortunate she lasted 4 years in her front seat until she outgrew it finally just this past March. I enjoyed and cherished every minute of our adventures with the front seat. They don't stay small forever, but I'm glad she at least will still ride me these days!



Originally Posted by WizardOfBoz
Andy, would you recommend that the rack stays be outboard, and the fender wires be inboard, to give a bit wider stance and resistance to lateral force?
I could be convinced to rearrange the rack stays and fender points if it provides better stability and safety...and just overall better for the rack and my bike. Not excited about having to bend the rack stays, but if it it's better then...
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Old 07-28-20, 10:32 AM
  #25  
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Wait to hear back from Andrew - he'll have a viewpoint with the advantage of deep experience.

But you DID torque the nuts, using LocTite, right? LocTite Blue 242*?

The reason I ask is that with the rack stays on the inside, a nut loosening and falling off leaves the thing setup such that a sharp turn could pull the rack loose from that side. If the rack is on the outside, even if the nut fell off your rack would be fine. Alternately, you could install the screw from the inside - this would avoid having to bend the stays and would give you a more reliable setup. To lose a rack fastener, you'd have to have the nut fall off AND the screw completely back out of the hole.

Then again, I'm an engineer and I may be overthinking this.

*"Blue LocTite" is generally meant to specify a threadlocker that is removable using standard hand tools. Whereas "Red LocTite" is meant to be permanent.
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