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Steel Fork straightneing

Old 01-09-20, 07:47 AM
  #1  
LawsonMitchell
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Steel Fork straightneing

Just picked up this Fuso FRX #550 ... But... And it's a big one! The front fork is bent from a collision. The fork crown is fine. I just need to find a mechanic in the Tampa Bay Area willing to straighten it. I talked to Dave Moulton, the builder, and he says it can definitely be straightened. The shops I've talked to keep saying they can't due to liability issues. Help!

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Old 01-09-20, 07:51 AM
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I have never found a shop willing to straighten a fork. Too much potential liability for too little money. My LBS doesn't even install tubular tires anymore. I talked to him about it, the increase in his insurance to cover doing tubulars was about 10X the income it would generate. So it was a pretty simple decision. So I adopted a D-I-Y solution.

Lots of DIY options have been discussed on this forum. I've straightened a lot of forks, but ONLY on my personal keeper bikes. My method is not as good as the one below. No interest in taking on this risk for others.

And in no way am I recommend you straighten the fork. Its really one of those decisions only you can make.

And be sure to inspect the main frame carefully. Typically I will find either slight rippling, or cracks in the paint on the DT and TT near the HT.


https://www.bikeforums.net/bicycle-m...bent-fork.html

Last edited by wrk101; 01-09-20 at 08:09 AM.
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Old 01-09-20, 08:01 AM
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Ship the fork to Dave Moulton?
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Old 01-09-20, 08:02 AM
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Unread 01-09-20, 10:01 AM
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dsbrantjr,

Dave referred me to a former apprentice. I'm trying to find someone in the Tampa Bay Area. Thanks.
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Old 01-09-20, 10:26 AM
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Try posting in the Framebuilders section as well. https://www.bikeforums.net/framebuilders/
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Old 01-09-20, 10:55 AM
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Considering the ramifications of a front fork failure, you might consider locating someone who definitely knows how to repair the fork (Dave's apprentice) than someone willing to do it.
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Old 01-09-20, 11:52 AM
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Get a long pipe, about a foot longer than the fork mask the fork so it doesn't get scratched, and go to town on it. You may have to take it to a bike shop to get the final alignment using a jig. But you can also just try riding it and if it ride straight with no hands, it's aligned.
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Old 01-09-20, 12:32 PM
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Originally Posted by San Rensho View Post
Get a long pipe, about a foot longer than the fork mask the fork so it doesn't get scratched, and go to town on it. You may have to take it to a bike shop to get the final alignment using a jig. But you can also just try riding it and if it ride straight with no hands, it's aligned.

So this is what I did with the help of a local frame builder. All straight & Aligned. Thanks to everyone, especially Dave Moulton, for the assistance.
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Old 01-09-20, 02:01 PM
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When we bent our forks jumping bikes, a junk wheel was installed, the fork turned around and wham! into the wall it went. This bent the fork blades back to straight (by sight, not measurement).
Another method is to install a dummy axle and use a lever against the crown to bend the blades in unison. Will need to measure for alignment either way.
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Old 01-09-20, 08:39 PM
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Originally Posted by LawsonMitchell View Post
So this is what I did with the help of a local frame builder. All straight & Aligned. Thanks to everyone, especially Dave Moulton, for the assistance.
As someone else suggested, take a hard look at the downtube to make sure its not kinked. If the head on hit bent the forks that far back, it could have very easily crinkled the DT.
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Old 01-09-20, 08:40 PM
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Ask me how I know.
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Il faut de l'audace, encore de l'audace, toujours de l'audace

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Old 01-09-20, 09:02 PM
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Originally Posted by LawsonMitchell View Post
All straight & Aligned.
Well done, get that beauty back out on the road.
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Old 01-11-20, 10:34 AM
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Dave is semi-retired

Originally Posted by dsbrantjr View Post
Ship the fork to Dave Moulton?
Dave is retired from building frames.

Dave Moulton's Blog - Dave Moulton's Bike Blog
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Old 01-14-20, 09:21 AM
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Originally Posted by San Rensho View Post
Ask me how I know.
How do you know?
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Old 01-14-20, 04:09 PM
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Originally Posted by Amt0571 View Post
How do you know?
I was in a 3/4 race on my 2 month old 3Rensho and had gone off the front but got caught. I was towards the back of the pack and as we go around a corner, the riders in front of me go left and right and theres a guy that had just crashed who is slowly getting on his hands and knees. No whrere to go I nail him on the hip, belly flop and skid on my chin a bit. The downtube was kinked, but I kept on riding it until it finally split, luckily the DT didn't separate, but the frame got really loosey goosey. I was like 20 miles from home and stopped and called a freind to pickme up. I dodged a bullet on that one.
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Old 01-14-20, 07:29 PM
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San Rensho, you rode home from the race with your chin split open? One tough SOB.
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Old 01-16-20, 02:21 PM
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When metal gets bent, it's molecules of the material getting torn apart. Those ripped apart molecules are typically too small to see. When you try to straighten a fork, you aren't putting those torn molecules back together, you tearing more apart in the vicinity. You aren't unbending, you are bending again in hopes of countering the deformed geometry. Get it looking straight and you have approximately doubled the damage you had after the initial bend. Steel is perhaps the most forgiving material. Aluminum typically just snaps off when you try to unbend it. Heating to red hot can allow you to alter the shape but it need proper annealing to regain some of the strength. On a bike like this one, the heat required would melt the brass in the crown.

Some times the steerer gets bent too. You never know what the weakest point of a bike is until it gets crashed. Sometimes the wheel fails, sometimes the frame gets bent, sometimes it's the steerer or blades. Rarely all are of equal strength. I've seen frames ripped apart in collisions where the fork and wheel were okay.

Look for cracks or ripples in the paint just behind the head tube. That's a sign the frame got damaged too.
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Old 01-16-20, 06:10 PM
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Originally Posted by rickpaulos View Post
When metal gets bent, it's molecules of the material getting torn apart. Those ripped apart molecules are typically too small to see. When you try to straighten a fork, you aren't putting those torn molecules back together, you tearing more apart in the vicinity. You aren't unbending, you are bending again in hopes of countering the deformed geometry. Get it looking straight and you have approximately doubled the damage you had after the initial bend.
This is not true, in general. There may be some micro-cracking
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Old 01-16-20, 08:51 PM
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So now I have to sleep with the guilt of tearing molecules apart? Andy
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Old 01-21-20, 07:56 AM
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All Straight. Thanks for all the advice.
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