Monday, September 21, 2009

Kuwahara Fork Problem Solved

After some fiddling around, I think I've gotten my Kuwahara fork bent back in to shape. Here's how I did it.

I started by bolting the fork to my workbench using u bolts - 1 1/2" for the steerer tube, 1" for the fork tubes.



Notice how the bearing cone extends beyond the steerer tube. I hand-tightened the nuts on the u bolts so I didn't bend the steerer tube.


After the nuts were all hand-tightened and very snug, I began bending with a 4' long piece of 2" dia PVC pipe. I used my right hand near the end of the pipe and my left hand on the work bench. If you decide to do this at home in this same manner, beware. It doesn't take very much effort to bend the fork. I wanted to bend only a very small amount at a time so I didn't over bend and have to bend back. I believe over bending and bending back will weaken the fork.

I used reference marks on the workbench to check my bending progress.
To check my progress, I placed a straight edge along the fork tube first on one side, then the other.

Doesn't look like much space here at the top of the steerer tube.

There's loads on the other side. I split the difference and measured from my reference marks near the drop outs. More bending to do.


I actually had to bend the other side - the side I thought was the non-bent side. I bent that in slightly toward the center, and pulled the bent side out again very slightly.

There, now the measurements are equal on both sides.

I had to do a little bit of bending to get the fork ends to be equal (level) on the front-to-back axis.

Then, the last item I checked before declaring myself done was to measure the drop out spacing. Perfect.
Fits like it should now.

One last item - since the fork had been bent, and I did more bending to get it back to close to factory condition, but not quite, the fork drop outs are not parallel. They should be parallel so they don't place too much stress on your front axle, and especially your skewer. A broken skewer equals broken bones or worse. Be careful. Take the fork to your local LBS to see if they have the whereabouts to fix this problem for you.

I did put the fork on my bike tonight and rode for a little bit. I can now ride no-handed on the Kuwahara!

10 comments:

Apertome said...

Very nice work! I'm impressed.

Rantwick said...

Wow, that was nicely done and documented. I also take great joy in seeing yet another excellent use for old bike tubes. They are so stinkin' handy!

Chandra said...

Bravo!

Steve A said...

I knew that once you had the problem tied down, it'd be quickly fi Ed. Bravo!

Mike J said...

Wow, that's pretty darn impressive. I would have messed that project up for sure.

Jon said...

Very similar to the method I use to rehab these old forks (although some are fixable while still in the bike).

Pretty much any bike shop worth its salt should have a set of dropout alignment tools. Have them do the rear drops, while you are there. Misaligned dropouts are the cause of most broken rear axles. (Sorry, to those of you who thought that you were such torque-monsters that you were snapping axles through brute force!)

Big Oak said...

Thanks to all of you for your comments. Thanks Jon, will have them check the rear dropouts also.

Oldfool said...

Don't you just love it when what you're fixing gets fixed without breaking something else?

Big Oak said...

OF - yes I do!

Gunnar Berg said...

Sorry for the late comment. I have a 1980 McLean that has a slightly crooked fork, probably as the result of an alteration somewhere along the line. I have considered various methods of straightening it, but because it's a valuable and irreplaceable bike, I have always turned chicken. I'll process your method for a while, but probably leave it to a professional anyway. Thanks for the info anyway. Good stuff. Incidentally, I stumbled unto your blog through Doug Robertson's (Duluth). I occasionally have bike related postings at:
http://oakwoodlife.blogspot.com/