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calling the 'bent fork police'

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calling the 'bent fork police'

Old 05-06-10, 10:44 AM
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calling the 'bent fork police'

A customer would like to me convert this Fuji S10-S into a single speed (no kittens will be harmed). In your opinion, is this fork bent?

There's a spot just under the fork crown with cracked paint that suggests a collision. The main frame tubes look and feel straight, and there is no other cracked paint like that on the headtube, downtube, or top tube. No buckles or ripples that can be seen or felt.





I can replace the fork with a chrome fork, and there are other frame choices that would fit the customer. But he really likes the Fuji. Thanks for your help!

PD

Last edited by Primitive Don; 06-22-10 at 08:48 AM.
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Old 05-06-10, 10:46 AM
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fork looks bent, have a closer look underneath the lower head lug on the downtube, the last pic looks like there might be cracked paint under there too.
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Old 05-06-10, 10:47 AM
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Busted.

The fork is bent.
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Old 05-06-10, 10:48 AM
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The ripples below the fork crown are compelling evidence and no jury on earth would fail to convict on this one.
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Old 05-06-10, 10:50 AM
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Man, you guys are much more responsive than the real police : ) Thanks for the quick responses

Originally Posted by Zaphod Beeblebrox
have a closer look underneath the lower head lug on the downtube, the last pic looks like there might be cracked paint under there too.
Will do!
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Old 05-06-10, 10:52 AM
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Case closed.
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Old 05-06-10, 10:53 AM
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Originally Posted by Primitive Don
Man, you guys are much more responsive than the real police : ) Thanks for the quick responses

Will do!
Wait until you get the bill...
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Old 05-06-10, 10:55 AM
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Bicycle Repairman comes to your door to collect....and you get a spanner to the head if you don't pay up
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Old 05-06-10, 11:09 AM
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From my experience and I am not recommending or suggesting that you do the same...

Back in the 80's, I bought a brand new Riggio/Viner frame/fork when I was working at this bike shop in Buffalo. Put the bike together and went out on a ride. Well, somehow at this curve, I was descending way to fast and lost control of my brand new bike and rode it right into a ditch. Head over heels, heels over head, bike over me, etc.

The fork was bent, both blades but I was able to ride back. A friend of mine was dabbling in frame building. We removed the fork and put on his jig. The fork was re-bent in a very scientific and precise method. I stood/jumped on each blade until the fork was aligned. We verified that it was true and straight. Mounted the fork right back on the bike.

This is my main and current bike No problems yet and I have not noticed any cracks. The fork was bent at the crown and not at the blades. Fork tubing is Columbus.

So maybe, you could re-bend the fork and see how it goes. One of the benefits of riding steel.

Last edited by yuyax; 05-06-10 at 12:55 PM.
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Old 05-06-10, 11:12 AM
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Bent fork is obviously bent. Just compare to unbent fork (sadly not my bike, but alas):


Bent Fork:
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Old 05-06-10, 11:40 AM
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Bent forks can be straightened but it requires skill and experience to do this right... replacement is usually the better option unless the fork is desireable / rare / of of very good quality.

This fork was bent... but it's a pretty nice bike.



I work with an experienced frame builder and send all work of this type to him as besides being able to restore things like this he also checks them magnetically to ensure there are no hidden failures in the brazing and welds... a bent fork may be just that and in extreme cases there will be damage behind the head tube... and if you really hammer it yo can actually bend the head tube.

The bike is looking better here... anyone with experience will know the fork was straightened as there are some small ripples in the paint... the repair was very well done and a little more subtle than jumping on the fork.

Steel is a very forgiving material while paint is not... different paint types and finishes will react differently when they are subjected to bending stresses and the Columbus fork was a good candidate for repair.



Looking much better here... the head tube is as straight as can be and the fork did what a good fork should do... it saved the frame from damage and there was no damage to the wheels as these with stand head on crashes better than forks do.

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Old 05-06-10, 11:45 AM
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Bent fork is indeed bent. In the first picture, on the downtube just under the cream-colored shifter handle, it looks like a spot of rust. If the paint is gone from there, check to see if there is a bulge. If so, the whole frame is toast, not just the fork.

That said.... when I did the same thing to my Nishiki, I straighted the fork by putting the fork ends between the steps of a paint ladder (while the fork was attached to the bike frame), and then pulling on the rear of the frame to straighten the fork. It didn't take a lot of force applied at the rear of the bike to straighten the fork (leverage, doncha know) and it was a very controlled straightening. I rode the bike a while longer but it's garage art now.
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Old 05-06-10, 12:03 PM
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My bent fork was similar to Sixty Fiver's Bianchi fork
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Old 05-06-10, 12:09 PM
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thanks all! I'm going to look over the downtube more thoroughly. If that checks out, the customer can choose between a new chrome fork or a different frame entirely. I have a Shogun frame that also fits which should also work.
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Old 05-06-10, 12:35 PM
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Having worked with metal, for many years, as a professional trades person, I honestly shudder at some of the back yard repairs reported in this thread. I do not say that to offend those who have tried and succeeded. I report my concern only for those people who might try to emulate your repairs, only to find out that they are not so lucky.

Stressing a brazed or silver solder joint is dangerous to the integrity of the structure. Unless you check the results of your cold setting work, with dyes or X-ray, you will not know for sure what the repair looks like. Cracks could well have formed that could fail suddenly and, perhaps, catastrophically, when under load.

When I straightened my frames or forks, I did my best to prevented a main stress from passing through a joint. All cold setting attempts were to the parent material only - the tubes or fork blades. I tried to avoid placing any stress on lugs or joints where a bend would be least likely.

If a steering stem is bent at the crown, I either pitch the fork set or replace the stem. I am a competent with a brazing or silver soldering process.

Just my opinion. And some people might suggest a propensity to analtivity:-)
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Old 05-06-10, 12:47 PM
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this is what chrome replacement forks are for, assuming the headtube area is undamaged.
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Old 05-06-10, 12:48 PM
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Originally Posted by Doohickie
n the first picture, on the downtube just under the cream-colored shifter handle, it looks like a spot of rust. If the paint is gone from there, check to see if there is a bulge. If so, the whole frame is toast, not just the fork.
I agree that it would also be good to look for any additional creases or bulges on the top tube and down tube, particularly right behind the lugs with the head tube. However lots of bikes can also get paint damage at the spot near the shifters from simple contact with the front brake caliper. Try turning the front wheel at a steep angle and see if that spot in the first picture corresponds to the location where the front brake touches the downtube. Contact with the caliper creates a very common cosmetic defect at that location, but not the kind of major structural damage that is sometimes seen in the main frame tubes after a front end collision.
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Old 05-06-10, 01:00 PM
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I can't believe you had to ask if that fork was bent. I think you're just wanting attention.
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Old 05-06-10, 01:13 PM
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Originally Posted by Primitive Don
A customer would like to me convert this Fuji S10-S into a single speed (no kittens will be harmed).
Isn't it nice that they don't have anything to be cut off for SS riders? I hope he keeps the pump braze-ons.

Originally Posted by Primitive Don
I can replace the fork with a chrome fork, and there are other frame choices that would fit the customer. But he really likes the Fuji. Thanks for your help!
Good taste.

What are you plans with the rest of that frame/components if he doesn't want the frame? If you are going to toss any of it or strip it down for donor parts, I could sure use the easily removable parts of the headset or the whole thing if you have the tools. Mine looks a bit rough up close, but it is a keeper.

Last edited by beech333; 05-06-10 at 01:19 PM.
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Old 05-06-10, 01:22 PM
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Originally Posted by gitarzan
I can't believe you had to ask if that fork was bent. I think you're just wanting attention.
Yep, that's me. Always in need of attention : )
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Old 05-06-10, 01:28 PM
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Originally Posted by beech333
Isn't it nice that they don't have anything to be cut off for SS riders? I hope he keeps the pump braze-ons.

Good taste.

What are you plans with the rest of that frame/components if he doesn't want the frame? If you are going to toss any of it or strip it down for donor parts, I could sure use the easily removable parts of the headset or the whole thing if you have the tools. Mine looks a bit rough up close, but it is a keeper.
No worries. We won't be removing the pump braze-ons or anything else, except for the fork : )

I will have to investigate the headset further, given the folk situation. PM me, Beech, if you are interested in any other parts (Maxy cranks, shifters, etc.)
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Old 05-10-10, 05:12 PM
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So I knew I had a 27" replacement chrome fork lying around, the ubiquitous Sunlite hi-ten chrome fork. Problem is the 200 mm steerer is not long enough for this tall frame.

Since we are going with 700c wheels, would I have problems moving to a 700c 1" threaded fork such as this one? That would give an extra 50 mm of steer tube.

The plan is to use Dia Compe centerpulls. I have short- and long-reach versions. Thanks for bearing with me.
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Old 05-10-10, 07:26 PM
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Incidentally Don, could you quickly measure the seatpost size? I need one for my S10S and I think it's a 26.4, but I'm not 100% sure.
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Old 05-10-10, 08:45 PM
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26.4
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Old 05-10-10, 11:19 PM
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Originally Posted by yuyax
My bent fork was similar to Sixty Fiver's Bianchi fork
What bent fork ?





Got to road testing the Bianchi and it runs out straight and true and you can take your hands off the bars and go no handed at 40 plus (kmh) with nary a worry.
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