Handlebar bolts

[pfm401]

Hello

My son has just bought a Calibre Bossnut (great bike!) to cut a long story short the handlebar bolts seem to be rounded off and I can’t get them torqued up properly (using a torque wrench) plus worry about loosening in future so I think the best thing is to replace them.

Any advice on good replacements? I’m pretty sure they’re M4 x20mm (pic attached). Does the material matter (steel / alloy) - don’t want them seizing in!

 

[Yellow Saddle]

Handlebar bolts have smaller heads than other commercial bolts, so your best place to start looking is at a bike shop.
Also, these are not just any old bolt, they are subject to plenty of strain cycles and thus have special profile thread and, the thread doesn't go all the way to the head. Get the right bolt.

Further, material matters. Aluminium (what I assume is what you mean by alloy, even though steel is also an alloy and aluminium is just, well, aluminium) is by no means suitable for the job.

 

[pfm401]

Handlebar bolts have smaller heads than other commercial bolts, so your best place to start looking is at a bike shop.
Also, these are not just any old bolt, they are subject to plenty of strain cycles and thus have special profile thread and, the thread doesn't go all the way to the head. Get the right bolt.

Further, material matters. Aluminium (what I assume is what you mean by alloy, even though steel is also an alloy and aluminium is just, well, aluminium) is by no means suitable for the job.

Thank you, yeah I agree a trip to the LBS it is. Never fan of guessing on eBay etc!

 

[fossyant]

Might be worth getting a set of assorted stainless bolts from Amazon/ebay - I purchased a used road bike a couple of years ago, and some of the bolts were rusty, so I replaced any with ones from an assortment pack. Worth having in stock.

 

[C R]

Also, these are not just any old bolt, they are subject to plenty of strain cycles and thus have special profile thread and, the thread doesn't go all the way to the head. Get the right bolt.

This caught my eye. Are they not ISO M4 threads?

 

[lostinthought]

This caught my eye. Are they not ISO M4 threads?

I suspect Yellow Saddle means that the bolts should have rolled threads (not cut) for durability's sake, despite the same size and pitch.

 

[C R]

I suspect Yellow Saddle means that the bolts should have rolled threads (not cut) for durability's sake, despite the same size and pitch.

Profile of the thread is independent from size and pitch, you could potentially have a thread with the same diameter and pitch as M4, but a profile different from ISO. This is what I understood from the post, but I suspect you are correct, they will be M4 threads with ISO profile but rolled instead of cut.

 

[pfm401]

Hmmm I'm sorry to sound stupid, but I tried an LBS plus a number of calls to Go Outdoors and Leisure Lakes bikes and so far striking a blank ...

So does the discussion about ISO and profile mean I can use a standard bolt (if push comes to shove) but it might not last as long? LBS said plain steel not stainless and recommended Screwfix!! Which ones have the galvanic corrosion issue does anyone know?

Seems a bit crazy to replace a stem for this without trying something, but safety first

 

[pfm401]

Sorry Go Outdoors stock the Calibre bikes and Leisure Lakes run concessions in the stores - they are the only sellers of Calibre bikes

 

[pfm401]

May try another LBS who seem capable of solving anything in my years with them - just a bit of a trek to get there!

 

[Yellow Saddle]

Might be worth getting a set of assorted stainless bolts from Amazon/ebay - I purchased a used road bike a couple of years ago, and some of the bolts were rusty, so I replaced any with ones from an assortment pack. Worth having in stock.

I wont do that, as tempting as it is to go rust-free. Stainless bolts don't have the required tensile strengthb for the job. However, I have no doubt that many people have replaced their stem bolts with stainless and lived to tell the tale. I don't want to deliver dire warnings, but there is a very good reason why these weren't stainless to start off with. After all, it is far cheaper to supply the stem with stainless bolts than going to the trouble of creating custom, heat-treaated bolts and coat them black or even chrome them.

 

[Yellow Saddle]

Profile of the thread is independent from size and pitch, you could potentially have a thread with the same diameter and pitch as M4, but a profile different from ISO. This is what I understood from the post, but I suspect you are correct, they will be M4 threads with ISO profile but rolled instead of cut.

Yes, rolled, instead of cut and then not threaded all the way up. Although the rolled thread is ISO, just like the cut thread, there are differences in appearance and underlying crystalline structure. You seem to understand the concept, but this may be of benefit to others.

Another place where standard hardware-store bolts fail is on seat post clamps particularly those with only one bolt.

 

[C R]

Yes, rolled, instead of cut and then not threaded all the way up. Although the rolled thread is ISO, just like the cut thread, there are differences in appearance and underlying crystalline structure. You seem to understand the concept, but this may be of benefit to others.

View attachment 761877

Another place where standard hardware-store bolts fail is on seat post clamps particularly those with only one bolt.

I thought that rolled threads were used only in smaller sizes like spokes, didn't expect it would make a difference in something like an M4.

 

[Profpointy]

I wont do that, as tempting as it is to go rust-free. Stainless bolts don't have the required tensile strengthb for the job. However, I have no doubt that many people have replaced their stem bolts with stainless and lived to tell the tale. I don't want to deliver dire warnings, but there is a very good reason why these weren't stainless to start off with. After all, it is far cheaper to supply the stem with stainless bolts than going to the trouble of creating custom, heat-treaated bolts and coat them black or even chrome them.

What grade bolts would you reckon are needed?

Instinctively at least I wouldn't have expected that was a particularly high stress application as you don't exactly do them up very tight - and if you do bollock them up tight I'd
be more worried about stripping the alloy.

Or is there more to it?

 

[Yellow Saddle]

What grade bolts would you reckon are needed?

Instinctively at least I wouldn't have expected that was a particularly high stress application as you don't exactly do them up very tight - and if you do bollock them up tight I'd
be more worried about stripping the alloy.

Or is there more to it?

Either Grade 5 or 8, IIRC. You are right that they are not torqued much, but they do undergo considerable cyclical strain (with strong athletes in anyway) and they are located in a critical place. Also, movement in the bolts results in erosion of the bar against the clamp edge. The brouhaha about stem bolts started when we moved from one M6 to four M4s in front-loader stems. There was an interimn period where the first front loaders either had a hook on the one end and a bolt at the other. These slipped and creaked. Then it went to two bolts, which still creaked and left gouges in the bar where the two parts work against each other. Today we have almost universal 4-bolt stems in quality stems with very few failures.

I doubt this is a problem for most of us. I'll confess that back in the day I experimented (without knowing I did it) on myself and a few of my mates with stainless steel capscrews. We had a statiscically significant number of failures. One female rider in our bunch was so freaked out by her seat bolt breaking frequently that she started developing a weight consciousness problem. I remember once she complained about her "jelly belly" having broken the bolt again. I was oblivious to the cause and kept on replacing them with standard stainless - probably A2, I can't remember. Later I looked into it, spoke to other engineers about it and eventually the penny dropped. We did a crude spark test on a bench grinder on a discarded bolt and the result showed high-carbon steel.

So yeah, I guess there is more to it.