Need help assessing fork damage
 

Hi

I was changing the stem/handlebars for a friend with the front wheel absent from aluminum fork. I placed for dropouts on a wooden box approximately 1' high. Accidentally the fork slipped and hit the floor when the bike fell. When we tried to insert the wheel back into the dropouts, it would not go in. I pressed on the fork blades to push them outside, and the wheel snapped in.

I looked at the dropouts, they did not look bent. What should I look for when assessing the damage? Cracks in the paint? I feel that this fork should just be replaced, especially given that this is not my bike.

Why did I try to change the stem with no front wheel? He had a problem with the front tire which deflated, and I suggested to take it out so that he could pump it while I was mounting the new stem. Yes, I know that the most dangerous mechanics are "experienced" home mechanics like me. Being able to successfully complete some projects results in overconfidence and loss of the sense of danger.

Your complication in my mind is that is not your bike and the liability is weighing heavily on you (reasonably), however if you are certain you see no crack in the fork end you might take the chance as aluminum is considered ductile. Strip the paint and look at the fork end aluminum surface. I had a fork dropped off of a shelf and used a buffer to polish it and clearly saw the crack so would not take the chance.

Just to be clear, the dropouts slipped off the wooden box and hit the floor with the bike in an upright position? The drop was one foot? You believe the space between the drop outs is now narrower than before the wheel was removed, to the point where you have to force them apart to mount the wheel?

Unless you can see that the dropouts are bent or have shifted position in the fork, (perhaps coming unglued); or that the fork blades are bent, have shifted in the crown (again perhaps becoming unglued), or the crown is bent, I would venture a guess that either the axle locknuts have moved outwards or nothing has changed, and this was not the first time the forks were spread to put the wheel on.

My guess would be that nothing happened to the forks, from a drop of one foot, but check with your friend, and go over the forks carefully, esp. the joints.

How far is it bent? You should measure 100 mm between dropouts.

Where is it bent? If it's one of the dropouts, you can tell by making a gauge with two pieces of all-thread and four nuts, similar to the Park FFG tool.

Hhjk

There are two dimensions of interest, and Andrew got em both. Measure between the fork blades. Should be 100mm +/- about 1 mm.

The dropout could have been distorted so that a properly sized axle won't fit. Check to see if either dropout is more closed than the other.

There is one other thing: modern forks have what are called lawyer's lips. If the QR was not open (unscrewed) far enough then that could make fitting the wheel in hard.

And also the brake might not have been switched to release mode and so its hard to get the tire past the pads.

Dropping an unloaded bike 1 foot onto the floor probalby should not have done much to the fork. But check dimensions....

Did the wheel go in easily before? Did this drop change things or just make you aware of a pre-existing condition? It is very often not the first bent that aluminum has trouble with but the bend back to straight. If this is a glued fork, it is entirely possible that it never had proper spacing and that the manufacturer either did not check or (wisely in my opinion) chose not to bend the blades. (The manufacturer could have sold it "as is" for cheap to someone who knew and accepted the issue.)

Ben

The drop has obviously ended with one or both fork tips getting squashed a bit. No biggie - just get a small to medium sized adjustable wrench on it and carefully open it up again. To be clear - I'm talking about the slot being narrower at the edge; you should be able to see it looking at the fork from the side.

Aluminum doesn't like being bent around much, but this is about as much bend as RD hangers are commonly subjected to; should be no problem.

If the forks are that delicate they should be thrown away anyhow. A front fork, even aluminum, has to be incredibly strong to withstand ordinary cycling use. You should be able to severely abuse it in a maintenance scenario without causing any dangerous damage. Now if you assemble the bike and deliberately run the bike into a stone wall at high speed, you're probably going to wreck the fork. Most anything short of that won't.

No. There's two different stresses going on here.

One is the normal compressive force the axle places on the drop out slot's closed end. I can't say I've ever seen a drop out fail from this compression. A number of other failure modes but not from this alone.

The second, and what we think might have occurred, is a bending force on one tip of the slot. This is quite possible and so well known that the LBS's largest wholesaler/supplier has warnings about not resting the fork on it's drop outs when slide hammering on the crown race. Dropping a fork onto one tip is much the same.

But this is one more reason to ride steel:) Andy