Rust...

Wrath Rob

My best bikes been playing up, the steering has gained a lot of "stiction" recently so last night I thought I'd tackle it. So I undid the top cap and stem and dropped the forks out of the head tube. Now, the nice bike is carbon frame and forks. I know that often carbon forks have an alu steering tube, as mine does. However, I wasn't prepared for the fact that carbon and alu can somehow rust! The bottom of the steering tube, where the bearing cups (right description?) sit had a lot of rust around it and some other build up on the alu as well. I cleaned it all off with some wet'n'dry, cleaned the bearings as best I could, greased the lot and re-assembled. Steering feels much better but not 100%.

So, where did the rust come from? I'm thinking its from the headset itself. If that's the case, does that mean its on the way out and I need to spend some money?

Whatever is happening, its further proof that you shouldn't ride your carbon bike in the rain...

gtvlusso

Aluminium does degrade, not rust, goes white usually as it degrades - looks like frost. It will be from the alu steerer and the headset bearings/set/cups. If there is actial brown rust - that will be from the headset bearings, probably steel races/bearings or sealed bearings.

I believe that carbon can degrade to, but this is more like osmosis and the carbon kindo of 'melts'

rjsterry

Nowt to do with carbon. The bearings will be at least partly steel - particularly the cups/cones - and probably not stainless steel. That's where the rust has come from. The corrosion on the steerer will be through galvanic corrosion, with salty winter road juice forming the electrolyte.

http://en.wikipedia.org/wiki/Galvanic_corrosion

Probably worth changing the headset bearings and being a bit more generous with the grease when you refit.

estampida

+1 on rjsterry

you can get carbon grease that stops specific metals from reacting but the might not be use on the bottom of the headset, these products were big when carbon bars came out, cos they had a multitude of different metals touching the bar (steel stem, alloy brake and gear levers, tri bars, alloy bar ends ect....)

fossyant

Rust is the bearings. Get some new ones !

tgotb

You definitely can get galvanic corrosion with carbon; it's just that it corrodes the metal part, not the carbon. In my sailing days we used to use a layer of glass to insulate metal fittings from carbon; if we didn't the results could be quite spectacular. I remember unpacking boats we'd shipped back from a competition in Aus, and one component on a carbon spar had transmogrified from a 2"x0.5"x0.5" precision aluminium casting, to a ball of grey fuzz with almost no solid metal left in it at all, in the space of about 8 weeks. That said, I've never seen anything like that on a bike, and unless you leave your pride and joy soaked in seawater for an extended period, I doubt you will either.

If you're seeing rust (brown), it will be from a steel component, almost certainly the bearings. Re-greasing will improve the situation, but you really need to replace the bearings (not the whole headset) as the corrosion will have left pitted bearing surfaces. The culprit is almost certainly not galvanic corrosion, just water getting into the bearings because there wasn't enough grease there to keep it out. Assuming your headset is from a mainstream manufacturer, it should be fairly easy to find replacement bearings.

bushu

ive got rusting on my brand new commuter, took the seat post off to attach a new saddle slyly at my desk and all the water getting down the back is rusting the post by the looks of it.
Should i just give it a good clean this weekend and apply excessive grease or blame wiggle?

estampida

you could replace the headset with 1 that runs ceramic bearings, as the material is non conductive it would isolate the fork and frame from each other, so just stem and bar to worry about

but full ceramic sets are thin on the ground and you will need a sitdown when you check the prices

cheaper alternative: http://compare.ebay.co.uk/like/29059870 ... sbar&cbt=y

Wrath Rob

Rust is normal brown rust so it sounds like the headset's shot. Will have to drop it into the LBS next week to get it sorted. Thanks gang.

rjsterry

TGOTB wrote:

You definitely can get galvanic corrosion with carbon; it's just that it corrodes the metal part, not the carbon. In my sailing days we used to use a layer of glass to insulate metal fittings from carbon; if we didn't the results could be quite spectacular. I remember unpacking boats we'd shipped back from a competition in Aus, and one component on a carbon spar had transmogrified from a 2"x0.5"x0.5" precision aluminium casting, to a ball of grey fuzz with almost no solid metal left in it at all, in the space of about 8 weeks. That said, I've never seen anything like that on a bike, and unless you leave your pride and joy soaked in seawater for an extended period, I doubt you will either.

If you're seeing rust (brown), it will be from a steel component, almost certainly the bearings. Re-greasing will improve the situation, but you really need to replace the bearings (not the whole headset) as the corrosion will have left pitted bearing surfaces. The culprit is almost certainly not galvanic corrosion, just water getting into the bearings because there wasn't enough grease there to keep it out. Assuming your headset is from a mainstream manufacturer, it should be fairly easy to find replacement bearings.

Oh yes, now I remember all those stories about CF fishing rods and power lines. So where does CF sit relative to the metals series? Is it more or less noble than, say, stainless steel. Or am I completely barking up the wrong tree.

PBo

gtvlusso wrote:

Aluminium does degrade, not rust, goes white usually as it degrades - looks like frost. It will be from the alu steerer and the headset bearings/set/cups. If there is actial brown rust - that will be from the headset bearings, probably steel races/bearings or sealed bearings.

I believe that carbon can degrade to, but this is more like osmosis and the carbon kindo of 'melts'

only the oxide of iron is rust....other metals oxidise.
problem with rust is it is hydrated iron oxide, and crumbles away to expose fresh iron - which rusts. Alu in comparison, does oxidise, but Alu oxide is pretty stable and the oxidised layer then protects the rest...

desweller

Most headset bearings these days are supplied as cartridge units.

Chances are that the oxidisation will have started on the outer surface. If the bearing feels OK in your hand then you don't need to replace the bearing; just use a piece of fine wet'n'dry to clean the corrosion up, make sure everything else in the area is clean and dry, then apply plenty of grease to the headset spacer seals upon reassembly to stop it happening again.