Replacing Bolts

[Reave05]

I'm trying to restore an old bike to turn it into a commuter. Pretty much all the current bolts have rusted. I was thinking I'd replace the rusted bolts as part of the restoration. What sort of process would I need to follow to replace the bolts? Simply take them out and measure them? Where would I find replacement bolts? Would I need to get them from a bike shop, or generic hardware store?

Sorry for the dumb question. I'm super new at this and am not at all "handy". I'm hoping to learn a lot on the way though.

[brokenbus]

Depends on the bike and the bolt or nut. Most bikes use M4 or M5 bolts for your rack and mudguard eyelets so you could take one out, go down to your local hardware or bike shop or specialist nut and bolt supplier and buy some stainless steel replacements for these. Be careful with disk brake bolts as i think they are hitensile and you need to replace with bolts that have the same rating.

[Warin]

Have to be a really old bike to use anything other than a metric bolt/nut.

Take a bolt (or a few of different diameters) to a hardware store and try them out on there range. They should have a display where you can test the fit of your bolts to confirm the thread. Try bunnings.

Once you have determined that it is metric threads then it becomes easy - the outside diameter of the bolt gives you the thread size; 5 mm outside diameter = M5 thread. The length is from the bottom of the head to the bottom of the bolt (not the overall length) in mm.

Some people go for stainless steel bolts - costs more but don't rust. These have a tendency to seize or gall ...you need to put some anti seize grease on the thread before assembly.

There are fine and coarse sizes of metric threads too ...never seen them on any bicycle, so just the plain standard metric threads. The coarse and fine threads have the same outside diameter but a different 'pitch' - bolt travel for one turn of the bolt.

[Reave05]

Thanks! That advice is incredibly useful for me. I'll take some out and go and check out Bunnings.

Cheers!

[ValleyForge]

...and check out Bunnings.

Speaking from experience - a specialist bolt & nut shop will be a better bet. Most hardware stores don't have the short length bolts that are necessary in bikes.

[Trevtassie]

Bunnings will be a waste of time, they have a very basic range and are expensive. Stainless is the way to go as chrome bolts aren't commercially available and zinc plated look like crap very quickly. 304 grade is usually sufficient for bike use. Take one of each needed to a good bolt shop and they'll match them for length. You can even decide on the head shape, button heads look nice, but because the allen socket is small need to be tightened with care. Socket headed cap screws are a bit more robust but have a chunkier head. Don't forget washers too. If you are screwing into aluminium then some teflon paste is a good idea, stop corrosion.

[Warin]

Bunnings (or a local bolt & nut place) will confirm the thread. And they have the 'popular' ones. I usually have a Bunnings shopping list so it is never a wasted trip.

Buying nuts/bolts over the internet can then be done with some confidence.

[silentbutdeadly]

...and check out Bunnings.

Speaking from experience - a specialist bolt & nut shop will be a better bet. Most hardware stores don't have the short length bolts that are necessary in bikes.

VF is most correct. Bunnings rarely supplies the specialist machine bolts with fine TPI threads that one would need even on an old bike

[RobertL]

...and check out Bunnings.

Speaking from experience - a specialist bolt & nut shop will be a better bet. Most hardware stores don't have the short length bolts that are necessary in bikes.

VF is most correct. Bunnings rarely supplies the specialist machine bolts with fine TPI threads that one would need even on an old bike

I agree with everyone above.

I've had to get a few specialist bolts over the years - not usually for bikes - and I have found that nearly every outer suburban, light industrial area has some sort of "Bolts R Us" type of shop. They will be able to replace whatever you've got - often in different choices of steel tensility(?), alloy type, head type and colour.

[antigee]

i've found ebay pretty good on this and I'm not a huge fan - bought both stainless and ti bolts from Asian sellers usually they are accurately described by use eg stem, waterbottle, rack etc and with pics so can work out what sort of head have - i tend to stick to sellers with high volumes / good feedback and work on the basis that if gets lost in post can i afford to lose it and can i wait for it - not had anything that I'd worry about the quality on and I've a background in metals distribution/industrial supplies

[QuangVuong]

If you're happy to pay for service, go find yourself a fasteners shop and bring in all the screws/bolts/nuts you're wanting to replace and they'll sort you out.

If you're a bit mechanically minded, then buy yourself some calipers and a thread/pitch gauge in metric and imperial(not really necessary for modern bikes). Good gauges will tell you the thread pitch and the 'standard' diameter for that pitch too. But to confirm, a set of calipers will do the job. For most thread sizes on a bike, you'll find the reading to be about 0.1mm smaller than the nominal size(4.9mm instead of 5mm).

304/316 stainless screws are nice to get, but class 12.9 steel screws are what you want if you're heavy handed with torquing up the screws, but will rust if not treated correctly. I've never used titanium screws as I don't see the benefit in weight and corrosion by paying more for a 'weaker' screw.

[Duck!]

Stainless bolts are NOT recommended for applications that are subjected to wracking/bending loads; on a bike this is primarily the seatpost head/seat clamp (some designs suffer more than others). Stainless work hardens, becomes brittle and eventually breaks. High tensile steel bolts are much better suited.

[RetroPilot]

Agree, Bunnings is a waste of a trip for stuff like this...they won't have the right thing, what they do have is gouge-priced, you will end up mostly wasting their time and your own piss-farting around the place.

Even ebay is a better bet than that, in general I've ordered many small packs of M4, M5, M6 bolts/screws from there.If it is more specialized stuff than ebay sellers can cater for, yeah, bolt specialists.Mostly cheap az, disadvantage is obviously you have to wait for delivery . With Bolt Bar etc, you will still pay through the arse,has to be that way because of the time-consuming nature of over-the-counter bolt interpreting and sales often for piddling nickel and dime orders, but at least they speak the lingo, I guess...save yourself the shed full of chicks and codgers in green aprons and blank looks, at Bunnings

[find_bruce]

Stainless bolts are NOT recommended for applications that are subjected to wracking/bending loads; on a bike this is primarily the seatpost head/seat clamp (some designs suffer more than others). Stainless work hardens, becomes brittle and eventually breaks. High tensile steel bolts are much better suited.

Hey duck, maybe you can do a bicycle version of Carroll Smith's classic nuts, bolts & fasteners

[Patt0]

Fleabay.

[zero]

Stainless bolts are NOT recommended for applications that are subjected to wracking/bending loads; on a bike this is primarily the seatpost head/seat clamp (some designs suffer more than others). Stainless work hardens, becomes brittle and eventually breaks. High tensile steel bolts are much better suited.

Stainless steel bolts don't work harden when fitted. It has to yield beyond its elastic limit to work harden (which is not how you fit a bolt). Its just cheap bolts with low yield strengths, stainless or otherwise, fatigue cracking that is the cause of failures.

[Duck!]

Yes it does. Stainless steel gear cables fatigue and break where they wrap and unwrap around shifter mechanisms from the repeated action. Stainless steel marine fittings which are subjected to repeated strain loads (e.g. having anchor lines tied off on then, and the repeated tugging from the wave action stressing the fitting). Single, vertically-loaded seat clamp bolts are subjected to a great deal of flexing load from the weight of the rider on the saddle. Side-by-side twin-bolt clamps are similarly stressed, and stainless steel WILL work harden and break in this situation. Fore-&-aft twin-bolt and horizontal single-bolt clamps are less obliquely stressed, therefore less prone to failure. Aerobar armrest bolts are similarly subjected to off-axis stress, and there are numerous instances of stainless steel bolts used in this application breaking where high tensile steel bolts have not.

[zero]

Work hardening of stainless steel only happens when it yields, and high tensile bolts, the bolts you are describing as the solution are extensively work hardened, because thats how you raise the tensile strength. You have to do it to the stock before you machine it though (cold rolling the stock), because it changes the shape.

I just find it amusing that you describe the solution as the problem.

The things that fail over time (or even to the initial loading) aren't work hardened, they are just fatigue cracked, or just not strong enough to begin with, and stainless has no particular property that makes it bad at handling fatigue, in outdoor (or sweaty) uses, its generally pretty good, because it doesn't rust and thus get surface pitting easily, and surface damage often raises local stresses and initiates fatigue cracking. ie given 2 bolts with the same tensile strength, likely to be loaded to the extent that the fatigue life is an issue, the stainless bolt is probably the better bolt for the application.

Also stainless bolts exist in all sorts of tensile strengths, it just so happens that its going to be more expensive for the same tensile strength, which is the actual substitution problem occurring in your aerobar example.

[RetroPilot]

So stainless steel inner cables are a bad idea?

[Duck!]

Sorta. They have a considerably smoother surface, therefore lower friction and slicker shifting than non-stainless cables, but the trade-off is that they will break eventually.

[Warin]

So stainless steel inner cables are a bad idea?

All things 'work harden' if they flex. The degree to which they harden is a function of the amount of flex and the material properties (youngs modus). Rope and string does well in terms of flex ware, but it will abrade fast if used in place of inner cables.

The worse idea than stainless cable is any cable wrapped around a small diameter drum .. as in those 'rapid fire' shifters. Some call them 'rapid failure'. The larger the drum diameter the less the cable has to deform, the less it will be stressed and the less it will work harden. This is why bar end shifters are popular with long term cyclists - the drum is just that little larger that the cable failure rate is much much less.

[baabaa]

Give jaycar a look if you have one of the larger shops nearby. The online catalogue may (or may not) help you find the right bits.
If it is on old bike I wouldn't be that fussy on how long the nuts and bolts will last, just find what fits best.

[twowheels]

If you are in Perth, this place http://www.westcoastfasteners.com.au/. I've used their services many times. Prices are good, will sell single items. (from experience always buy more than you need though.)