Hank3

I did not use threadlocker because I was under the impression that using a nylon lock nut was sufficient? But I do have some blue threadlocker (Loctite) and can certainly apply some on the threads of the nylon lock nut/bolt.

79pmooney

Maybe I'm not getting all of this but - I would put the rack inside the dropout, fender outside and run the bolt from the inside. That way the bolt is just working as bolts are supposed to, It's hardly going to care that you burdened it with a lightweight fender nutted to the outward facing extension. (Another plus - you get to choose a bolt head that works with your cassette and chain; pan head or even flat head (after countersinking the fender stays).

And yes - if you go SS use marine grade. 304 or 316, They are formulated specifically to not do galvanic corrosion with aluminum. I'd have to do my homework but I bet quaility non SS, especially zinc plated would do better than cheap SS. Use lots of grease! Anti-seize might be the best. Marine grease certainly isn't going to hurt.

It sounds to me like you have been experimenting with the metal combinations sailors avoid.

Ben

WizardOfBoz

If you look at an earlier note, I mentioned threadlocker OR a nylock nut. Note that the bolt has to extend all the way through the nut (the bolt tip should extend one or two threads past the nylon for the locking part to work). II suspect that the approach advocated by 79pmooney, above, is going to be extra dividends with a nylock nut, as those types of nuts take up more space and extend further into the area where the chain and stuff are.

But I think you've got it right: rack and fender stays on opposite sides. And if the bolt extends into the nylon far enough, you should be fine.

It's funny how a little thing makes a difference, eh?

Hank3

I see one thread beyond the nylock nut on each side. Next bolt size up (35 mm) would be too much I'm afraid, but not if I go from inside out. And still debating if I should venture to bend the rack arms out to accommodate the outer position and switch the fenders to the inside. How many times can you loosen a nylock nut before its deemed useless?

WizardOfBoz

Wait til Andrew weighs in. May be worth a PM to him. I think you're ok, though. The key thing is that the bolt has to have the nylon part engaged.

If I had to do something, I'd reverse the screws without changing the bending pattern. This jmakes the failure mode for the rack falling off either a bolt shear failure, or the head popping off due to shear loading. Both a LOT less likely than the nut falling off!

Seriously, though, you've done a very good job of asking questions and actually listening. A lot of times you'll see someone ask a question "Can I touch up my Imron paint job with spray can enamel?". And folks will write in with great expertise, like "I worked for DuPont in their automotive paint group, and the proper touch up is ________." And the poster will ask a few more questions, and then write in "I used spray can enamel". Arghh!

Anyway, good luck.

Hank3

Thank you, WOB. I certainly am a novice when it comes to this kind of stuff. Just trying to do my due diligence in ensuring the safety of me and my daughter (really more my daughter), and that I'm not doing anything to ruin my bike and parts.

I've read all of the comments on threading the bolt from inside and having the nylock nut on the outside, however, since the eyelet threads are smoothed out now, I'm trying to figure out why this orientation provides and extra barrier of protection? So that if the nut falls off it goes outward and not into the spokes?

WizardOfBoz

I'm an engineer. We condsider what is called "failure modes" and consequences for different design cases.

Both design cases: rack stay on inside, fender stay on outside.

Design Case 1: Nut on inside.
Description: Nut on inside, holds rack, bolt screwed in from outside, bolt head holds fender.
Failure mode 1: nut loosens and falls off. Rack stay can become detached with a hard turn to the side opposite the nut, especially with loaded rack or trail-a-bike. Failure mode frequency (nut loosening) is common.
Failure mode 2: (Requires failure mode 1, first) Bolt unthreads and falls out of threaded eyelet. Then both rack and fender are loose. Failure mode frequency highly unlikely. Would notice failure mode 1 first.
Failure mode 3: Bolt head fails and detaches. Results in fender stay coming loose Failure mode frequency low, as bolt is in shear loading.
Design assessment: Failure mode with significant consequence (rack stay detaches) due to fairly common failure (nut loosening).

Design Case 2: Nut on outside.
Description: Nut on outside, holds fender stay, bolt screwed in from intside, bolt head holds rack.
Failure mode 4: nut loosens and falls off. Fender stay can become detached. Failure mode frequency (nut loosening) is common.
Failure mode 2: (Requires failure mode 1, first) Bolt unthreads and falls out of threaded eyelet. Then both rack and fender are loose. Bolt might interfere with chain/freewheel. Failure mode frequency highly unlikely. Would notice failure mode 1 first.
Failure mode 3: Bolt head fails and detaches. Results in rack stay coming loose Failure mode frequency low, as bolt is in shear loading.
Design assessment: Likely failure mode results in loss of fender stay, less catastrophic.

The point is that you probably want the bolt head holding the rack, and not the nut. And because the fender stay loss is less catastrophic, you want the nut on the fender stay. And if you don't want to change the bend of the rack stay, then the easiest design improvement is to thread the bolt from the inside.

Make any sense?

WizardOfBoz

But again, if your nylock engages properly you should be good to go.

Hank3

Thank you for detailing that out...really appreciate it! And it does make sense. I think I was getting stuck because since the eyelet is no longer threaded (I filed out the threads) I assumed the bolt would slide out of the eyelet regardless of it being outside in or inside out. But I guess with it being inside out, there's more bolt that has to fall towards the wheel for the rack to disengage from the bike.

WizardOfBoz

Ummmm. Ok. Why did you file out more metal from the eyelet? Not to be a jerk, because you are trying (and didn't grow up working in a metalworking shop and a bike shop) but the next time you have the urge to remove metal... don't.

As an after-the-fact Dutch uncle kind of thing, the actions when you have morked-up threads are (in increasing level of severity)
1) Do nothing. Just screw in a new screw or bolt and see what happens
2) Form tap. A form tap is just a tapered bolt made from hardened, super-strong steel. You screw it into the existing hole and it squashes ("cold works") the metal back into proper thread form. It doesn't remove any additional metal if you already have threads. If you have a significantly strong (e.g. non-stainless, higher grade steel) screw or bolt, you can use that as a form tap. Use oil and thread the thing thread the existing threads. This is kind of the least intrusive.
3) Thread chase. This is a kind of cutting tap that minimizes the cut taken. A chasing tap really isn't idea for cutting new threads, but it works well to clean out old ones. Removes a minimal amount of metal.
4) Tap. This is a thing that looks like a bolt but has grooves cut into it. When you screw it into a hole, it cuts new threads. Removes maybe a skosh more metal than a chaser.
5) Thread repair. You drill out the hole to a larger diameter, and use a tap to cut threads of the same pitch (threads per inch) as the old thread. Then you screw in a thread insert (a coil of diamond shaped wire) into the new hole. This forms new threads of the same size and pitch as before. Results can be very good, as the insert is designed to stick in place. Look up "thread insert" for details.
6) Drill (or file!) out hole to make non-threaded hole. This loses and lateral force on the bolt and allows a bolt that looses its nut to shift. Sub optimal.
7) Replace eyelet. Structural welding on aluminum frames is not practical, so this option is out.
8) Replace frame.

Removing the threads from the eyelet kind of jumped to the more extreme end of the swimming pool, and weakened the assembly. You're probably still ok, but I'd definitely put a new longer screw on from the inside and get it long enough to protrude a couple threads past the nylock. And you should make sure that the bolt you select is pretty nearly the same size as the hole you've filed. May need a bigger bolt. And don't remove any more metal!

Hank3

I think at this point, the hole might still be small enough to run a tap through it. I have a M5 tap on hand but will need to source a tap wrench and give that a go. Maybe go up to a 35mm length bolt; run it inside out with more threads protruding out of the nylock nut.

Andrew R Stewart 

No, if they both have to share the same bolt the rack goes inboard of the fender struts. This placed the rack's load in a more shear direction then a bending one, WRT the bolts. Andy

WizardOfBoz

Hey, Hank, I learned something and you put your rack and fender stays on correctly. Kudos! Thanks, Andy.

WizardOfBoz

Well, first, if you can slide the bolt in and out without turning, tapping's not going to do anything but scratch up the inside of the hole. If this is the case, check to ensure that the bolt isn't so loose as to rattle around. (If it does, I suppose some shim work might be useful.)

If you can't just slide the bolt in and out, and you must turn it to get it into the hole, great! Leave things alone and assemble with the bolt head on the inside (near the rack stay). In this way, if you lose the nut, your fender falls off but not your rack.

In short, removing more metal without knowing what you are doing can only hurt and cannot help. As a general point, though, form tapping is much preferred to using a cutting tap in aluminum anyway, especially so in small holes where taps break easily.

Hank3

Well that certainly wasn't by design...LOL. Pure coincidence due to path of least resistance, but I'll take a win when I can.

Now to less win things. Both eyelet holes have barely any threads remaining. The M5 bolts I'm using right now are basically through bolts. They slide through the holes easily which I'm assuming means that a form tap wouldn't be the right thing to use at this point?

WizardOfBoz

A tap is only going to form or cut metal if there is metal to cut. If you have a through hole, neither tap will do much of anything. In my estimation, you have three choices
1) Check to see if the bolt is held in place (that is, is the hole so large that the bolt rattles around in the hole). If the bolt fits pretty closely in the hole, assemble with no further filing or cutting.
2) If the bolt is rattling around a bit I suppose you could try a steel shiim wrapped around the bolt to get it so that it isn't too loose. Again: no filing or cutting.

If either 1 or 2 work, great. You are probably going to do 1 or 2. If you want to go crazy on this, method three is:

3) You could have what is called a thread repair kit installed. This involves drilling the hole out a bit, and then tapping with the same pitch. An M5 bolt has a pitch of one thread per 0.8mm. So you'd drill the hole out with a drill provided in a kit, and tap with (for example) a 6mm tap with 0.8mm pitch. Same thread pitch, bigger hole. Then you'd put what is called a thread insert into the hole. These are designed to go into the hole and stay there. The insert is made of diamond-shaped wire such that the inside of the insert is standard M5 thread. Because you'd want the holes drilled very accurately, and you'd want the tapping done by someone who won't break the tap off in the hole, it might be prudent to have someone with a machine shop do this.

Hank3

Option 3: I have used something very similar before on my car. It was called a Heli-Coil kit. Worked out really well actually, but not sure I want to do that in this application.

The bolts do fit pretty closely in the holes right now. I've been monitoring the bolts and nylock nuts after the last two rides and they haven't moved (yet). I know that doesn't mean I'm outta the woods...because I've put myself (and more importantly my daughter) in a somewhat compromised/less than ideal situation due to my inexperience

I certainly do appreciate all of the information you have brought to the table to not only educate me for the future but to also give me additional things to consider. So I can try to enjoy things as they are currently are but remain vigilant in how the bolt/nut arrangement are. Go back to the larger Cannondale that still has good eyelets. But the whole reason I bought this newer Cannondale is because the size is a better fit for me and I prefer a 1 by setup in the front for the type of riding I do.

WizardOfBoz

Sounds like you're good to go without the radical surgery. That's great. A key point is that the rack bolts are loaded in shear and not tensile, so the threads don't have a lot of force on them. Keeping vigilant is a good idea.

Yup, you nailed it: Heli-coil is one brand name, and probably the most popular. And there's slightly different versions available from different companies (Keensert and others). If you've done this you know that it requires a good drllled hole (preferably on a drill press, with your bike held down with a proper fixture or ad hoc work-holding tools), a good tap (again, you have to be sure that the tap is aligned with the hole), all with proper lubrication. So its good you don't have to do this!

Enjoy the riding with your munchkin.

Hank3

Thank you again, WOB. Too bad we didn't live closer to one another or else we'd go for a ride and I'd buy you lunch. Here's a pic of gratitude and appreciation:

Andrew R Stewart 

We tweak rack and fender stays often to fit or clear stuff as needed. I want the rack stays and the frame eyes ro fit as square/parallel to each other as possible to minimize anything having a bow or flex as the bolts are tightened up. Neutral fit up, IME, means less stress and loosening. But I also believe in one bolt/one job. My own bikes reflect this mantra. The touring frames have a lot of self made bits to locate and isolate stays and such from each other. One of my pet peeves is the disconnect between the bike designers and the accessory guys. Even if the bike and the accessory are from the same "family" it's frustrating to see incompatibilities as often as the LBS does.

As to whether the OP should reconfigure his rack and fender stay "stack" I think his current set up (as in post 18) is actually pretty good. There's chain/cog clearance, the rack strut in up tight against the eye and the fender strut clears the rack. I can't see but the bolt would be best run from the inside to outside with a nylock nut clamping the fender strut. Widening the rack struts to the outsides of the eyes won't cure the rack's lack of triangulation. Andy

Hank3

Thanks for the extra info, Andy!