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Can't unscrew bike peddles from aluminum crank arm

August 6, 2008

I have a big problem with a bike crank I own. I have had some clipless bike pedals with a cromoly spindle that attaches to an aluminum (anodized, I believe) crank arm. While trying to remove them I have found them nearly impossible to remove and so I wonder if something else is going on. I am no stranger to rusted bolts or tough screws and am normally prety capable. However in this case the Cromoly spindle does not want to come out. With all the tools I have used I have also applied Liquid Wrench [affil links] and other lubricants/de-rusters. Normally you would use a 6mm hex key to unscrew it on the opposite side. It is so stuck it broke a hex key and striped (into a circle) two other ones. A professional bike shop had a hard enough hex key, but after a lot of work, ended up striping the hex socket. I still kept trying though.
I tried a pair of Vise-grips and an actual vise on a table to try and clamp on tho the small spindle and get it loose, but to no avail (the cromoly is so hard, it deformed both tools).
This is the hardest thing to get loose I have ever tried. Is something more going on like maybe Galvanic Corrosion or a Contact weld? I am also assuming that when they installed the pedals they didn't use enough grease.)
What are any possible next step suggestions?
Any recommendations on strong chemicals to get into the joint and help undo the two pieces (I work in a lab and have access to lots of chemicals/solvents) Strong acids/Oxidizers?
Would using a butane torch [on eBay or Amazon] to expand the cromoly be beneficial as well? (but nothing is really able to grab the spindle tight because the cromoly ends up breaking it)
I really don't want to drill the spindle out as it would be incredibly destructive and hard to do. Any suggestions appreciated.

David Bracho
Hobbyist - Ann Arbor, Michigan, USA

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August 6, 2008

Doncha just hate aluminum sometimes? The threads would not be anodized, so there can be and apparently has been a reaction where the aluminum in the threaded area has corroded (oxidized) into space consuming corrosion products, thoroughly jamming this up. Aluminum oxide corrosion products consume twice the space of the raw aluminum. It is theoretically possible that an anodizing shop could remove this aluminum corrosion with a chromic-phosphoric anodizing stripper in the thread area without destroying the anodizing on the rest of the crank, but it sounds dicey. With proper care for your safety you could try a few dots of oven cleaner [on eBay or Amazon] foam in the thread, but this dissolves aluminum as well as aluminum oxide.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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I seriously doubt that this is your problem since you've already gone to a bike shop, but remember that one side of your crank arm / pedal combination is reverse threaded. If it weren't, the pedal would unscrew in pretty short order.

If the crank set is worth keeping, another option would be to drill it out and ruin the pedal. The hardness of the spindle would probably make this a futile effort.

Leo Sharkey
- Fridley, MN, USA
August 8, 2008