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Bent triples/forks/trees - diagnosis

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Here's the deal, I had a machine shop alter a steering stem for me, I've had them do work in the past and it was no problem.

This time, instead of leaving the the steering stem on and sticking it in a lathe, they cut it off, put a new piece on a lathe and created what I asked for, then welded the new piece in for the steering stem. It looks perfect.

Since this was part of a project, the donor the forks came off of never was ridden. I assumed the forks were straight.

Mount everything up and the forks are bent. Curse a few times, head off to ebay and buy replacement forks.

Replacement forks arrive, mount it up and it's bent the same way! ARRGH!

So I did what I should have done the first time, I checked all four forks for straightness using a framer's square (not a T-square) as a straight edge, on the stanchions.

All four appear to be perfectly straight.

So, that leaves the triple trees being screwed up, right?

Before I go to the machine shop and ask them to check their work, I'd like to see if there's anyway I can check it without having to take the bike apart again.

Is there anything else that would cause the trees to go out of whack?

I don't know how I would check the stanchion/lower combination for being straight though.

It's a ball-bearing bottom/top steering stem assembly, if that makes any difference. Could the bottom or top race not be perfectly straight?

Thanks.

Edited by Smacaroni

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Nt sure why they were welding anything relating to the steering stem. I'm not sure teh contruction of yours but typically you press out the old one and press in the modified stem. Welding causes serious problems with distorsion and for a precision alignment that forks require, it is not a good method.

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The factory piece was welded, I presume that's why they welded the replacement.

I've got before/after photos, but I don't think there's enough precision to make them worth viewing.

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Get the engineering shop to put the stem "between centres" on a lathe and spin it. If it's not straight it will be immediately obvious.

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I assume that when you say "bent", you mean that the wheel points in a direction other than what the bar would indicate is straight ahead. If this is the case, first be sure that the bars themselves aren't bent. Following that, try loosening either the upper or lower pinch bolts and pushing the wheel into the correct position and see if it wants to stay there.

If the condition persists, you can lay a sheet of glass across the installed fork legs to verify that they are in fact out of line. Try rotating one fork tube 120 degrees, then the other, to see if that changes anything. If not, may have a set of twisted clamps, or possibly bent handlebar mounts. You should be able to loosen one fork leg and slip it smoothly in and out of the clamp with the other side still tightened.

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