Ed Holland

Update:

I finally had time to takle the frame. I did a complete strip of the bike, and removed paint down to bare metal (a lot of hard work). She was then coated with aluminium primer & sanded, then 3 top coats were applied with sanding in between. There are no pictures of the rebuilt bike, but here are some I took along the way with my cellphone camera (please excuse the quality). I took the opportunity to overhaul all the components, so she will ride like new when there is a good weather day here - I can't face getting her filthy on the first ride...

Cheers,

Ed

2manybikes

Nice looking paint job. Photos not bad for a cell phone.

garynchait

I just bought an 80s aluminum framed Trek used for my son. Got it home and noticed corrosion on the seat tube near the front derailleur. Attached some images. Is this what your frame looks like?
So, is it dangerous to ride the bike with this corrosion present, i.e. could the seat tube crack now or sometime in the future?
Thanks.
-Gary

puchfinnland

What you have going on there is Galvanic corrosion.

we had a simmilar case on a half year old bike.

the owner just left his custom made frame bike out in the weather all summer,
the bottle bosses are steel rivnuts, the little plastic cable guide under the BB has a stainless screw holding it in,

you will need to strip the bike down completly,
locate all the places alu and steel come in contact.
have it glass beaded, and then proper aluminum primer and a paint job.
grease every steel screw and component before putting it back together.

notes
headset are prone to cause trouble also
are the pop rivits on the cable guides stainless or steel?
the cable housing ends? plastic or shiny steel? replace with plastic shimano type
the bottlebosses-steel rivnuts?
was the BB greased before it was threaded in?
a drainhole in the frame bottom is a wise idea before repainting.
grease every screw and adjuster.

you could even put plastic tape between the front deraileur and the frame to help

macelius

Just picked up this '94 Klein Quantum Z, rides perfect but the guy used it as a trainer and apparently never washed or even wiped it down. The white alu oxide powder was as thick as 1/16 under some of the larger bubbles, but after a wire brushing the tubes don't look that bad, though there is some minor pitting around the bottle cage mounts. Going to be hard to replicate the original finish, so it might end up just plain forest green or orange. Still looking for replacement decals.

beechnutC23

Sorry to revive a dormant thread but I have significant corrosion on my 23 or so y.o. aluminium mountain bike, where the paint peeled away. As a former aircraft owner I can assure readers here that aluminium does indeed corrode. The oxide layer wears off, eventually reducing the thickness and strength of the metal as each successive layer forms then wears off. My aircraft was built in 1979 and I owned it until last year. Repairing corrosion was a continuous process at each annual inspection and the worst area was under the floorboards where people's wet boots would drip into. Corroded areas were sanded down lightly and treated with zinc chromate primer; I spent a couple of days at my last annual inspection sanding down corroded areas under the floor; it's best to get on top of it as quickly as possible to avoid the need to replace structural elements ($$$). When the aluminum is pitted like it is on my mountain bike, on an aircraft structural component, it won't pass annual inspection. I don't do any rough mountain stuff with mine, just gravel roads, but it's serious enough that I think I will finally retire the bike at the end of the season. Good opportunity to build myself a nice gravel bike

(N+1)-1+1 = N+1

Johno59

Al will eventually corrode to mush - especially so wherein salt and damp air are in abundance. Crashed WW2 aircraft I played in as a kid in the jungle that still had decals, inflated tyres, rubber coated wiring, seating etc are now white coloured dirt.
Heat (welding) and stress flexing ( bottom bracket,chainstays) accelerate the corrosion.
Wire brush it down and keep going until firm paint /clean shiny metal is reached. Clean with solvent, prime and paint. Use a brush, it's Al after all. That should solve the aesthetic problem and should outlast the rest of the paint work. If crap returns in the exact location before anywhere else - you need to consider a new one. There is virtually zero chance of a catastrophic failure - as in a delamination point in carbon. It will just go mushy to ride and start crabbing off a normal line.

davidad

Look at the welds, it's aluminum.

Abu Mahendra

yeap. Al welds tend to be higher profile, thicker. Steel welds, more smooth, discrete.

Some people confuse corrosion with rusting. Al alloy will not rust as such, but will corrode.

i've got paint chipping off too on my Al alloy bike, and i also think it is due to sweat/salt corrosion.

davidad

My only claim to fame was building a portable helicopter landing pad for the old Calypso. We used WWII scrap aluminum laying around in the shipyard. The GMAW's were soother than TAW, but still rougher than steel. I haven't seen an aluminum weld that was as smooth as other metals.

Khoorxr

This is filiform corrosion.

fietsbob

+1, Strip and repaint.


Pay for a powder coat job .






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