Re: [CR]fixing a bent crank arm (Duncan Granger)

(Example: Framebuilding:Tubing)

In-Reply-To: <022120052009.29306.421A400F0000E11F0000727A22007348409D0A09020E9D090B@comcast.net>
References: <022120052009.29306.421A400F0000E11F0000727A22007348409D0A09020E9D090B@com cast.net>
Date: Mon, 21 Feb 2005 19:30:37 -0500
To: dgranger@comcast.net, classicrendezvous@bikelist.org
From: "Sheldon Brown" <CaptBike@sheldonbrown.com>
Subject: Re: [CR]fixing a bent crank arm (Duncan Granger)


Quoth Duncan Granger:
>I thought I would pass this along, since I searched the archives
>before I tried it, and didn't find any reference to fixing or
>straightening bent crank arms.
>
>I am in the process of restoring an older (1957) English bike with a
>cottered Nicklin chainset. The drive-side arm was bent in, towards
>the frame. I removed and cleaned the chainset, and took the pedals
>off the arms.
>
>To straighten the drive side arm, I put it in a 400 degree (F) oven
>for five minutes, then with oven mitts ran it up to my shop, put the
>pedal end in the bench vice with the arm pointing straight up and
>the chainwheel at the top. I then slipped the handle from a socket
>wrench into the hole for the BB spindle, and pushed down. I had to
>put my whole weight on the thing. However, the result was that it
>actually bent back very close to straight.

Actually, there's a much easier way to do this. It helps to have an assistant.

Unscrew the pedal, lift the bike up and clamp the end of the crank into a vise (the assistant tightens the vise while you hold the bike in position) then use the bike as a lever to bend the crank back straight.

Do NOT do this with an aluminum crank, but it's reasonably safe with a steel crank.

I don't believe 400 degrees F is hot enough to make any practical difference in the malleability of a steel part.

Sheldon "Leverage" Brown Newtonville, Massachusetts +-----------------------------------------+ | There is a remedy for everything; | | it is called death. | | --Portuguese Proverb | +-----------------------------------------+ --
    Harris Cyclery, West Newton, Massachusetts
       Phone 617-244-9772 FAX 617-244-1041
            http://harriscyclery.com
       Hard-to-find parts shipped Worldwide
            http://captainbike.com
    Useful articles about bicycles and cycling
            http://sheldonbrown.com