Bicycle Mechanics - damaged fork, maybe drop outs just bent?
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11-22-12, 08:11 PM
Hi, I have a vintage trek 420 frame which I have been holding onto to build a 650b bike when funds allow. I finally got some wheels to test the fit etc and discovered the fork is not straight. The frame was given to me and had come from someone who collected old bikes to fix up and sell and all came from donations, abandoned, found at the dump etc. So it's just something I didn't notice as it is not obvious. My husband thinks if he puts the fork in a vice with some clamps he can straighten the fork drop outs which look slightly bent. they are true temper 4130. Should I take it to a bike shop or frame builder? Is it something so easily fixed, would a hack job be a safety issue?
Most/all the bike shops around here won't touch a bent fork (I tried). So I do my own. Before doing anything, you need to make sure the main frame triangle is OK.
Andrew R Stewart
11-22-12, 09:28 PM
http://www.bikeforums.net/showthread.php/858441-Fork-Steerer-Alignment-Is-there-a-simple-test This linked thread has a discription how to check a fork's alignment with simple tools. The question of how to align a bent fork safely is the bigger one and best left for some one with a lot of experience. BTW the force that caused a fork to bend can also warp or bend the frame as well. So take that into your examination and assesments. Andy.
11-23-12, 03:01 AM
Thanks, bummer, I will have to check main frame too. This frame has sort of had a bad time, sitting unused for quite awhile, maybe not meant to be. I almost sold it too, would have felt bad for the person who bought it and realized the fork was bent if not the frame as well. If the frame is okay, I guess a new fork might be easier? At least I have another frame I can use instead, but that was meant for another project.
Depending how badly bent the fork is, straightening is not difficult. In addition, generic replacement forks are readily available.
A bent main frame, damage is often first seen on the top tube and down tube, near the head tube. You will see a ripple on the underside of both tubes, and the paint will be chipped or cracked. The ripple can be felt with your fingers. Of course, more extensive damage will be more obvious.
Simple test I use to spot a bent fork. Once you get an eye for it, it is very easy to spot a front to back bent fork. We routinely call out bent fforks over on the C & V forum (you can mentally draw a line just like my straight edge below and see many bends):
Bike in work stand:
Then use a straight edge (a yard stick works fine), centered on the stem bolt, through the center of the head tube, and through the center of the fork crown. If the fork is bent backwards, the fork blades will appear behind the straight edge. Of course, this does nothing for a side to side bend.
11-23-12, 07:11 AM
If it's just the dropouts it is ok to straighten them. There is an alignment tool made for this job. http://www.parktool.com/product/frame-and-fork-end-alignment-gauge-set-ffg-2
11-23-12, 09:45 AM
There's also the Park FT-4 to check blade alignment:
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