Bicycle Mechanics - Frame damage?
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08-10-10, 12:51 PM
Here are two forks off of 60cm Trek frames. I'm thinking the fork on the right is bent. A wrench at a major chain store looked at it on the bike but didn't think so.
I didn't see any paint ripples or cracks on the top tube or on the down tube.
What does it look like to you?
Also, the bottom bracket shell on the same bike has some odd dimpling on the front. The adjustable cup has two slight depressions on the inside. I'm wondering if that also signifies impact damage.
08-10-10, 01:01 PM
I agree that the fork on the right looks a little tweeked. It isn't much so not surprised it wasn't noticed by the wrench.
The BB shell looks to have chain damage on the one side and possibly a little damage caused by someone removing the BB at some point on the other side. Neither of these looks impact-related.
08-10-10, 01:19 PM
If the picture isn't distoring the right hand fork it's certainly bent. Line up the steerer with the front of the upper legs and there's a bit of sweepback already. Let alone the bending that is pretty clear midway down the leg that has the back line running straight instead of being tapered like the one on the left.
The BB damage looks to me to be more from heavy handed tool useage than due to crashing. It's pretty tough for anything to hit in there thanks to the chainrings and crankset.
08-10-10, 01:39 PM
Right fork looks bent....BB shell looks OK.
I also agree the fork looks bent in the photo. Possibly the actual bend is at the base of the steerer and hidden by the crown race. You can do an eyeball check by putting the steerer to your eye and sighting down it like a rifle. It isn't so bent that I wouldn't ride it on a hack bike, but it might not handle well enough your serious bike. You'd have to ride it to know for sure.
One problem you might face is that if the bend is in the steerer or at the base of it it'll effect headset performance since the crown is off axis. You'll know right away when you install it because the crown race will appear to rock as it's turned, the fork will be loose or tight depending on orientation, making headset adjustment difficult if not impossible. (Cheap headsets are more forgiving in this respect than quality ones).
BTW- this isn't so serious a bend that a skilled mechanic cannot straighten it. That was routinely done for years but went out of fashion because of product liability paranoia. If it were my fork, I'd install it check the headset adjustment, and steering, and if OK leave it alone, otherwise I'd straighten it and use it.
08-10-10, 02:36 PM
This is why we always used Var #478 (http://www.sheldonbrown.com/var/pages/var0006.html)
08-10-10, 03:02 PM
was that built as a fixie? On the BB it seems like the kind of paint scratches you'd get from rotafixing. Doesn't look like a major problem in any case.
08-10-10, 05:18 PM
Yep, a lot of the bend looks like it's either in the lower portion of the steerer tube or perhaps the cast crown lugging has twisted.
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