Straightening a fork- how bent is too bent?
06-30-20, 09:12 PM
#1
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Straightening a fork- how bent is too bent?
I’m wondering what the limits are for straightening a fork? No other frame damage, kinks, or bulges to be seen but clearly someone ran into something in the past.
Anyone with experience, or advice about how to proceed here? Thanks in advance!
Anyone with experience, or advice about how to proceed here? Thanks in advance!
06-30-20, 09:18 PM
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It doesn't look too bad. I'm sure it can be bent back.
06-30-20, 09:40 PM
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I really didn't see anything, but then I spotted that the crown race isn't square with the bottom raceway.
If it's steerer tube damage, that can be straightened too - but never that well or square. If it is steerer tube damage, you're probably better off looking for another original Moto fork.
However, the blades don't actually look overtly bent to me. The front geometry on some of these had quite a bit of trail, and some French and English builders tended to align the tapering the back edge of the fork blade with the centerline, thus making the front edge of the blade taper backwards before the bend forward.
What I do see is that the whole crown looks kinked - which does support the theory that the steerer tube is bent - but the lack of major damage makes me wonder if there's the slightest chance that the crown was brazed off center to the steerer from the factory.
Drop the fork and take some photos of the lower part of the steerer tube for us.
-Kurt
If it's steerer tube damage, that can be straightened too - but never that well or square. If it is steerer tube damage, you're probably better off looking for another original Moto fork.
However, the blades don't actually look overtly bent to me. The front geometry on some of these had quite a bit of trail, and some French and English builders tended to align the tapering the back edge of the fork blade with the centerline, thus making the front edge of the blade taper backwards before the bend forward.
What I do see is that the whole crown looks kinked - which does support the theory that the steerer tube is bent - but the lack of major damage makes me wonder if there's the slightest chance that the crown was brazed off center to the steerer from the factory.
Drop the fork and take some photos of the lower part of the steerer tube for us.
-Kurt
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06-30-20, 10:09 PM
#4
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...as above, it's pretty hard to tell without pulling the fork out of the head tube. The issue with a bent steerer (as opposed to the fork legs), is that even if you can bend the thing back to where the fork ends were originally (thus restoring original trail), you can still end up with a fork where you cant get the crown race to be correctly oriented to the rest of the headset. So it ends up not turning freely through the full rotation.
Sometimes the magic works, and sometimes it doesn't.
...as above, it's pretty hard to tell without pulling the fork out of the head tube. The issue with a bent steerer (as opposed to the fork legs), is that even if you can bend the thing back to where the fork ends were originally (thus restoring original trail), you can still end up with a fork where you cant get the crown race to be correctly oriented to the rest of the headset. So it ends up not turning freely through the full rotation.
Sometimes the magic works, and sometimes it doesn't.
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06-30-20, 10:56 PM
#5
Senior Member
It looks okay to be bent back to position. You might want to take it to a frame builder because there are always things the naked eye can't see that easily. Might be over kill, but still worth a shot.
It could be worse. This is my first Miyata that I bought ignorantly as I didn't know much about bikes at the time and just wanted a touring bike. For $100, it was an affordable lesson learned. Cool parts were functional so I parted it out. Top tube and downtube were badly bent, inspected, and sprayed over but someone. The fork was badly bent and there was no way of using it anymore (according to a $20 consultation from a frame builder).
It could be worse. This is my first Miyata that I bought ignorantly as I didn't know much about bikes at the time and just wanted a touring bike. For $100, it was an affordable lesson learned. Cool parts were functional so I parted it out. Top tube and downtube were badly bent, inspected, and sprayed over but someone. The fork was badly bent and there was no way of using it anymore (according to a $20 consultation from a frame builder).
06-30-20, 11:10 PM
#6
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Camera angles can sure make something look worse than it is. If you want to drop it off at the Atelier, I'd be happy to diagnose. If the steer is straight and the fork crown isn't bent up, I can get the fork back to where it should be. I've had several Motobecane's, particular like your Grand Record in the shop and know what the rake should be.
PM me if you're interested for a socially distanced fix.
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06-30-20, 11:15 PM
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looks like an easy one
these steerer deformations just above the crown are quite common
with the fork out of the bike i take a half round file to the interior of the lower end of the steerer to deburr it
then i have a long mandrel just the right diameter to go up inside
with the steerer clamped in the vise using wooden blocks made for the purpose i use the mandrel to do the cold setting
check everything with a straight edge
when steerer looks good put fork in alignment gauge to double check everything and make sure no other cold setting is needed
then back in the bike and robert is thine uncle
whole thing takes no more than three or four minutes
-----
looks like an easy one
these steerer deformations just above the crown are quite common
with the fork out of the bike i take a half round file to the interior of the lower end of the steerer to deburr it
then i have a long mandrel just the right diameter to go up inside
with the steerer clamped in the vise using wooden blocks made for the purpose i use the mandrel to do the cold setting
check everything with a straight edge
when steerer looks good put fork in alignment gauge to double check everything and make sure no other cold setting is needed
then back in the bike and robert is thine uncle
whole thing takes no more than three or four minutes
-----
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06-30-20, 11:19 PM
#8
framebuilder
Your fork looks like it is well within the range that it can be bent back to original rake. I've aligned hundreds of frames in many years of framebuilding and it is uncommon that a fork is so damaged that the steerer is bent too. Usually in those cases the top and down tube are obviously bent too so the whole frame is trashed. Fork blades are designed to be bent a lot. They start straight and are bent around 1.75"/2".
06-30-20, 11:24 PM
#9
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Thank you all for your thoughts about this situation. I will pull the fork tomorrow after work and take some photos of what I discover
06-30-20, 11:46 PM
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Then, with the front wheel, handle-bars and front caliper removed, spin the fork 360 degrees. Does it spin smoothly or does it bind?
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07-01-20, 01:40 AM
#11
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Little Big Eh?
23" - 58cm C-t-T 1974-1977 Grand Record.Those bikes came with a seamed straight gauge steerer that had a sleeve brazed into the bottom rather than a butted Reynolds 531 steerer.
Here's the steerer from my 1972 Le Champion which was the same frame as the 1974-77 Grand Records except for lugs and chrome socks on the rear triangle.
Here's the sleeve in a Peugeot UO-8 fork crown.... Same idea. Motobecane, Peugeot, Raleigh and many others used this to save a few pennies, centimes, lira?
Ed Litton has the fixturing and could straighten that in a few minutes. Unfortunately he's recovering from ankle surgery and will be of for a few months.
After straightening and realigning the fork, the crown will need to be refaced.
It's best done on a lathe because these forks were chrome plated and the the plating will tear up the cutter on a fork crown refacing tool.
Also, while the fork is out, it would be a good idea to reface the head tube.
Wana trade again?
verktyg
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07-01-20, 06:25 AM
#12
framebuilder
Are you wanting a black and red Motobecane like the one in the OP's picture? I made a frame for a customer years ago that maybe still has one. I remember the color when he brought it by to show me years ago but I don't remember the model or year. I don't think he is sentimental about his. I can always ask.
07-01-20, 08:14 AM
#13
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Wana trade again?
verktyg[/QUOTE]
Chas- this one is a bit big for me (like the Lazzaretti), but I had picked this up with the thought to rebuild it for my son. He’s 6’-1” so it should be a better fit for him.
Regarding a trade; whatcha got?
verktyg
[/QUOTE]Chas- this one is a bit big for me (like the Lazzaretti), but I had picked this up with the thought to rebuild it for my son. He’s 6’-1” so it should be a better fit for him.
Regarding a trade; whatcha got?
07-01-20, 08:36 AM
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this is bent too much. T boned a car at 21 MPH:
P1030232 by superissimo_83, on Flickr 
P1030233 by superissimo_83, on Flickr 
P9051190 by superissimo_83, on Flickr 
P1030230 by superissimo_83, on Flickr
P1030232 by superissimo_83, on Flickr P1030233 by superissimo_83, on Flickr P9051190 by superissimo_83, on Flickr P1030230 by superissimo_83, on Flickr
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07-01-20, 08:39 AM
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^ I see the distinction!
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07-01-20, 09:10 AM
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Are you wanting a black and red Motobecane like the one in the OP's picture? I made a frame for a customer years ago that maybe still has one. I remember the color when he brought it by to show me years ago but I don't remember the model or year. I don't think he is sentimental about his. I can always ask.
-Kurt
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07-01-20, 10:26 AM
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07-03-20, 12:57 PM
#18
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The steerer tube appears to be straight, and once I received some assurances (and a kind offer from Gugie) that it could be straightened I decided to undertake a bit of a spiff-up.
The Ideale saddle, tires, red toe straps, bar wrap and red cables all came out of the used parts bin. The Universal 68 sidepulls came out of the same bin, having been removed a decade ago from a bike I bought in 1977. I’m always happy to recycle what I can!
The Ideale saddle, tires, red toe straps, bar wrap and red cables all came out of the used parts bin. The Universal 68 sidepulls came out of the same bin, having been removed a decade ago from a bike I bought in 1977. I’m always happy to recycle what I can!
07-03-20, 01:29 PM
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I really didn't see anything, but then I spotted that the crown race isn't square with the bottom raceway.
If it's steerer tube damage, that can be straightened too - but never that well or square. If it is steerer tube damage, you're probably better off looking for another original Moto fork.
However, the blades don't actually look overtly bent to me. The front geometry on some of these had quite a bit of trail, and some French and English builders tended to align the tapering the back edge of the fork blade with the centerline, thus making the front edge of the blade taper backwards before the bend forward.
What I do see is that the whole crown looks kinked - which does support the theory that the steerer tube is bent - but the lack of major damage makes me wonder if there's the slightest chance that the crown was brazed off center to the steerer from the factory.
Drop the fork and take some photos of the lower part of the steerer tube for us.
-Kurt
If it's steerer tube damage, that can be straightened too - but never that well or square. If it is steerer tube damage, you're probably better off looking for another original Moto fork.
However, the blades don't actually look overtly bent to me. The front geometry on some of these had quite a bit of trail, and some French and English builders tended to align the tapering the back edge of the fork blade with the centerline, thus making the front edge of the blade taper backwards before the bend forward.
What I do see is that the whole crown looks kinked - which does support the theory that the steerer tube is bent - but the lack of major damage makes me wonder if there's the slightest chance that the crown was brazed off center to the steerer from the factory.
Drop the fork and take some photos of the lower part of the steerer tube for us.
-Kurt
One where to take everything off the fork, then turn the fork around as much as possible, protecting the top tube. Observing for a change in tightness or looseness.
The drop the fork, and get it into a fork alignment tool.
It is off, just were exactly...
I hope not the steerer, I do not think those should be straightened. Replaced, but then an alternate fork is probably cheaper, will require a new headset and stem
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07-03-20, 01:44 PM
#20
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Here's a beautiful, imo, paint job on a World Tour that I lifted from the Bod Jackson website. That Grand Record scheme, the Gran(d) Sport(s) white and blue and this Jackson are probably my favorites.
07-03-20, 05:39 PM
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I just posted the same question on the frame builder forum about a Norco Monterey with a bent fork.
Andy Stewart would have done it but border closed. Went to frame builder here who dug out a tool called a "little brute" (actual name). He hadn't used it in decades so might be obscure and hard to find.
Upside down bike. Tool hooked on fork. Worked like a jack. Cranked it about 5 clicks. Tool off checked alignment. No. Try again. Not yet. 3rd time, Bang on. Time elapsed three minutes? Had to realign forks and done. Wish I'd photo'd the process.
Andy Stewart would have done it but border closed. Went to frame builder here who dug out a tool called a "little brute" (actual name). He hadn't used it in decades so might be obscure and hard to find.
Upside down bike. Tool hooked on fork. Worked like a jack. Cranked it about 5 clicks. Tool off checked alignment. No. Try again. Not yet. 3rd time, Bang on. Time elapsed three minutes? Had to realign forks and done. Wish I'd photo'd the process.
07-03-20, 06:27 PM
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I just posted the same question on the frame builder forum about a Norco Monterey with a bent fork.
Andy Stewart would have done it but border closed. Went to frame builder here who dug out a tool called a "little brute" (actual name). He hadn't used it in decades so might be obscure and hard to find.
Upside down bike. Tool hooked on fork. Worked like a jack. Cranked it about 5 clicks. Tool off checked alignment. No. Try again. Not yet. 3rd time, Bang on. Time elapsed three minutes? Had to realign forks and done. Wish I'd photo'd the process.
Andy Stewart would have done it but border closed. Went to frame builder here who dug out a tool called a "little brute" (actual name). He hadn't used it in decades so might be obscure and hard to find.
Upside down bike. Tool hooked on fork. Worked like a jack. Cranked it about 5 clicks. Tool off checked alignment. No. Try again. Not yet. 3rd time, Bang on. Time elapsed three minutes? Had to realign forks and done. Wish I'd photo'd the process.
RJ the bike guy to the rescue:
