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General Category >> Technical >> Can Carbon Crankset Arms Be Shortened?
https://rbentonline.org/YaBB.pl?num=1460153411

Message started by jayg on Apr 8^th, 2016, 5:10pm

Title: Can Carbon Crankset Arms Be Shortened?
Post by jayg on Apr 8^th, 2016, 5:10pm

Cut the end of an FSA carbon crankset arm off to see whether or not its threaded aluminum insert was long enough to permit shortening a 175 mm arm to 150 mm in my home machine shop. Was hoping the insert extended pretty far up the length of the arm. Unfortunately, it does not. So, if you use a crankset with arms less than 165 mm on your recumbent, you are flat out of luck, if you want to install a reasonably-priced FSA carbon crankset. A 160 mm Lightning Dynamics carbon crankset, less chainrings, costs $680. [smiley=jawdrop.gif] Note: The crank arm was defective (donated by Daniel S), so I didn't destroy a usable crank arm.

http://i1021.photobucket.com/albums/af339/jayg_2010/SAM_0030_zpsqnqssl2j.jpg (http://s1021.photobucket.com/user/jayg_2010/media/SAM_0030_zpsqnqssl2j.jpg.html)

FSA crank arm with end sawn off.

http://i1021.photobucket.com/albums/af339/jayg_2010/SAM_0035_zps6wgtvahp.jpg (http://s1021.photobucket.com/user/jayg_2010/media/SAM_0035_zps6wgtvahp.jpg.html)

Threaded aluminum insert in end of crank arm is very small.

http://i1021.photobucket.com/albums/af339/jayg_2010/SAM_0036_zpsdd1ouvt2.jpg (http://s1021.photobucket.com/user/jayg_2010/media/SAM_0036_zpsdd1ouvt2.jpg.html)

Sawn end of crank arm. Other than the aluminum insert, I expected the arm to be of solid carbon fiber construction (carbon fiber fabric in an epoxy matrix), but it in fact has a couple of longitudinal hollow channels filled with loose rolls of carbon fiber fabric. The recess in the center was occupied by the aluminum insert's tang, before it was removed.