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Spreading fork blades?

Old 12-08-05, 01:23 PM
  #1  
grolby
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Spreading fork blades?

I'm looking to make it possible to switch front wheels between my good bike and the winter beater I'm putting together. This was going to be a simple operation, but then I took out the ruler and it turns out that the beater's fork is sized to the 91mm standard! I'd like to be able to switch wheels so I can put a wheel with an aluminum rim in there - the bike came with steel rims, and it's obviously not worth it to build an alloy wheel up with a 91mm hub.Is there is a safe way to spread the blades of a 91mm fork to accept 100mm front hubs? The fork is basic hi-ten steel, so no problems with the materials, but I don't know if I'm taking chances with geometry or the integrity of the fork crown. I also don't know how I would move it by an even 4.5mm each way, which is why I'm asking if there are any techniques for doing this. Thanks!
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Old 12-08-05, 02:14 PM
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Your LBS might have a jig for fork repair. I had mine do a similar bending job. It does weaken the fork a little bit, but are you really worried about that on a winter beater?
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Old 12-09-05, 03:16 AM
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If you have a cheapo bicycicle and a mountain like no suspension fork, you can use a car jack to open the fork. For me, opened evenly in both sides. But remember this is what I made for me at home. Do it in your own risk.

A better solution is to replace fork.
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Old 12-09-05, 11:46 AM
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I haven't done this on a fork but i've used this technique on a rear triangle. Put the fork in a vise, take a two by four and put it between the fork blades legnthwise all the way down to the fork crown. Pull towards you to bend one blade. Be careful when bending, the idea is to slowly increase the force that you are applying until you feel the metal bend. When you feel the slightest give of the metal, stop, check how much it bent and bend more if necessary.
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Old 12-09-05, 11:53 AM
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there is a hand bar clamp that you can switch around to use a spreader, I don't remember the name but they are blue and yellow and avialable at your local independantly owned hardware store, (or home despot).
I used one to spread a front fork wide enough to hold a rear MTB tire (my truing stand).
just work slowly (and carfully) practice if you have the salvage lying around
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Old 12-09-05, 12:53 PM
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A slightly more elegant way then the 2x4 is to get a piece of 3/8" all-thread rod, two washers and two nuts. Thread the nuts onto the rod, put the washers on the outside of the nuts and adjust the distance between them until the washers will just fit inside the fork dropouts. Back out one of the nuts slowly to spread the fork blades. Stop often and check your progress. Continue until the new hub will just fit. This gives you the best chance of spreading the blades symetrically.
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Old 12-09-05, 12:57 PM
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Originally Posted by HillRider
A slightly more elegant way then the 2x4 is to get a piece of 3/8" all-thread rod, two washers and two nuts. Thread the nuts onto the rod, put the washers on the outside of the nuts and adjust the distance between them until the washers will just fit inside the fork dropouts. Back out one of the nuts slowly to spread the fork blades. Stop often and check your progress. Continue until the new hub will just fit. This gives you the best chance of spreading the blades symetrically.
Nice solution!
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Old 12-09-05, 01:12 PM
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Originally Posted by HillRider
A slightly more elegant way then the 2x4 is to get a piece of 3/8" all-thread rod, two washers and two nuts. Thread the nuts onto the rod, put the washers on the outside of the nuts and adjust the distance between them until the washers will just fit inside the fork dropouts. Back out one of the nuts slowly to spread the fork blades. Stop often and check your progress. Continue until the new hub will just fit. This gives you the best chance of spreading the blades symetrically.
Hey, that sounds like a good idea! And low-tech enough for me to do. It might also work with a spare Sturmey-Archer axle I have - the flats will give me something to hold onto with an adjustable wrench while I back the nut off.

Thanks you guys! This might just work!

EDIT: Whoops! Not so much with the axle. Gonna have to make a trip to the hardware store, alas!

Yet Another EDIT: Some testing has made it clear that the entire project is pretty much impossible - the fork ends are too narrow to take a QR axle! Thanks for all your help anyway, it was much appreciated.

Last edited by grolby; 12-09-05 at 01:31 PM.
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Old 12-09-05, 05:36 PM
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Yet another post! It suddenly occurred to me that it isn't impossible. What's the word on filing the fork-end drops out to fit the larger QR axle? The difference in size appears to be only 1-2mm or so, 3 at most, it seems like I could get away with this without causing any serious problems. Am I right about this? Thanks!
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Old 12-09-05, 05:54 PM
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Originally Posted by grolby
Yet another post! It suddenly occurred to me that it isn't impossible. What's the word on filing the fork-end drops out to fit the larger QR axle? The difference in size appears to be only 1-2mm or so, 3 at most, it seems like I could get away with this without causing any serious problems. Am I right about this? Thanks!
Dremel away!
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Old 12-09-05, 06:20 PM
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Originally Posted by grolby
Yet another post! It suddenly occurred to me that it isn't impossible. What's the word on filing the fork-end drops out to fit the larger QR axle? The difference in size appears to be only 1-2mm or so, 3 at most, it seems like I could get away with this without causing any serious problems. Am I right about this? Thanks!
Done frequently.
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Old 04-02-08, 09:19 AM
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I hope someone reads this post, I know that this thread may be dead, but I am having the same problems, actually both problems I need to spread the fork and I need to file the dropouts to accept the larger bolts on the hub...You say dremel away, can someone please be more specific... Like what is a good step by step proceedure that a newb could follow?

Thanks a lot
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Old 04-02-08, 09:54 AM
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Now that this thread is back, I thought of one more solution. Get a new fork.

Bike shops should be crawling with steel take-off forks from riders who have upgraded to carbon forks. These will have the right dropout spacing and axle diameter and should be very cheap. You will probably have little trouble matching the required steerer length and spacers can be used to fit a slightly too long steerer to your frame.
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