Need41speed

I’ve got a Retrospec “Spec” (Judd) folding bike that I’ve modified over the years. I’ve noticed the frame hinge bolts are starting to corrode. Looking for advice on replacing these with a more corrosion resistant (titanium?) fastener. Any takers?

Top view- top hinge bolt

Bottom view- bottom hinge bolt

Iride01 

Anything special about the part of the bolt we can't see? Big long shoulder and a few threads on the other end that are significantly smaller diameter? Might just get several of the same and just change them out as they get cosmetically unattractive to you.

If the it's just the head that's rusty, then clean it up and put some paint on it. Maybe just a zinc primer or some cold galvanize spray paint.

maddog34

Most hardware stores stock Stainless Steel bolts, screws, and nuts in a variety of configurations.

titanium can also corrode... and may cause surrounding materials to fail.

just curious,, how often do you actually "fold" the bike?

Need41speed

Have not disassembled the hinge yet, was fishing for someone who has taken apart this frame joint. In just superficial observations, the “hex bolts” appear the same. The joint length is 5cm & the bolt head 5mm hex.

Need41speed

Will look into sealants to protect the bolt head. I fold both my folding bikes (also have a Dahon Mu) quite often, 2-3X a week, loading into my car or entering an establishment.

maddog34

i'd opt for some stainless allen bolts and stainless nylock nuts.

salty air does bad things to plain steel.
salt is a chloride.
soak the stock hinge pins with penetrant oil now.

tiger1964 

That part, and that part alone, reminds me of what I've read about aviation bolts, specc'ed by "grip length". Alas, that's all I've ever read about them and never utilized any...

Crankycrank

Whether you keep the bolts or get new ones make sure to put some grease on them when installing to prevent corrosion.

base2 

I'll wager that it is an unusual fastener type. One end is a long barrel that is the full diameter of the hole and fills the hinge from end to end for the full length. The other end is a standard bolt that threads into the first to retain it in place.

Why not wire brush the bolts to remove the gross corrosion, soak them in Coca-Cola to convert the remaining fe3 & reapply the failed few atoms thick layer of phosphorus passivation (if there ever was one), apply a bit of primer to bond to and keep the new layer protected. Then apply a decorative top coat of any color you like to seal the primer away from weather?

The job would be trivially cheap to do.

poinciana

To be certain I'd need to see the fastener out of the frame, but it looks like the exact part you need is a "Hex Drive Binding Barrel and Screw" - which you can get in stainless from McMaster-Carr: https://www.mcmaster.com/products/bu...ls-and-screws/

Just measure it well (preferably with a caliper) and you should be good to go. Be careful that it isn't just slightly too long (if they don't have the exact size of what the bike came with), or it may bear against itself rather than the frame. Some grease on the shaft and blue loctite on the threads would go a long way as well.

JoeTBM 

Exactly what I would do. Agree that the barrel is long, like a pivot bolt from a mountain bike suspension pivot bolt

base2 

Good find. Exactly what I was thinking but couldn't recall the name of. +2 internet points to you, sir!

I would think that in this particular application, a tiny fraction long so that it does bind against itself, and not the hinge would be a positive. That way the twisting of the hinge action doesn't exert a torque on the two halves relative to eachother causing it to loosen. Still, a thread retaining compound like Loctite in such a safety critical bolt is still sage advice.

mpetry912 

Right, when I saw the allen heads on both ends, it's a suspension pivot bolt, I'd bet.

pull it out, take some measurements, and go fish. I found the below with 15 seconds of searcning eboy "MTB suspension pivot bolt titanium"

this is eboy 145147162510 but there are lots of choices. 10 buck.

you will need to take the length into account. Looks like these have a threaded tube between the bolts.

and this is one application where some grease - inside and out - will work in your favor.

/markp

poinciana

Agreed, and the original bolt is probably sized to do just that. Just something for the OP to be aware of, since usually something like a 5mm longer bolt is a total non-issue.

Of course, a washer or two would take care of that anyway, in the off chance it needed it.

Iride01 

Thanks for the other pic, that clears things up quite a bit. Although you showed both sides in the first two pics, I didn't swap the bolt to the other side and realize that there is a head on both sides.

I've had seat post clamp bolts like that. They were the ones I typically broke often as the threaded part is so much less diameter than the other part it threads into. Though I don't remember any bikes having one that would span that distance. However a couple other members gave you good hints on what to look for and search for on the internet.

You also might just go down to your local dealer for that bike and see if they have or can get some for you. But if you have to improvise something, stainless steel would be my preferred material. 316L if you can find it. Maybe at a marine supplier if you just decide to go with a regular bolt and nut. 304 stainless, which is the common SS you find, will in areas of salt breeze not hold up as well.

Still, if you take that out. Clean it up with a wire brush and spray with some zinc based primer will likely last a decent amount of time with a touch up every great once in a while. Just don't over torque it and break it when you put it back in.

WizardOfBoz

IIRC, "AN" bolts come only in inch designations. But perhaps I'm mistaken.

mpetry912 

yes, pretty sure this is true. But the "grip length" measurement is still valid.

the NAS (New Aircraft Standard) has been extended to account for metric dimensioned fasteners.

/markp

WizardOfBoz

Thanks, Mark. I owe any knowledge in the area to a dated reference: "Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook", published 1990. Appreciate the update.