DIY: How to straighten Forks

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DIY: How to straighten Forks

Postby Franko » Mon Dec 01, 2008 5:59 pm

Ohhhh, great MC Gurus....

I purchased a 98 YZF600R front end to upgrade my 86 VFR. Just before reassembly, check the straightness of one of the forks, and it is BENT about .054".
Measured with v-blocks and a deflection gauge.


At the highest point, I did this:
Image
The 2x4 in the clamp has a 43mm round 1/2 circle cut, so I don't flatten the fork from the force.
So far I have taken out .012" and have .042" to go...

It is interesting to note: when I bend the fork tube ~.160", that would only take out .001-.002" of the bend. It took me about 6-8 tries to get the bend down to .042"

The cheap c-clamp was not able to handle the force and bent. I needed a different way of doing this. After many ideas, I came up with this:
Image

  • I have two pieces on angle iron (one was not enough!!) back to back.
  • On the left is an old clip-on from a CBR F4 (41mm dia)
  • On the right is an upper triple from a CBR F2 (41mm dia)
  • The big clamp is from my Princess Auto universal joint tool

The trick is to hold the tube with something round, so you don't flatten the tube. The old upper triple & clip on worked great. The tube has a max of .001" out of round.

In the middle I used:
Image
  • 2" PVC plastic tube with one side cut. (so it fits over the fork)
  • Then I bent some .060" sheet metal as a spacer and to help spread the force
  • Then a 2" x 3" nipple (it has a smooth surface on the inside)

Every inch I would find the low spot, reset the deflection gauge, and mark the high spot.

I would deflect the fork about .200" for 30 seconds at the high spot. That would take out about 0.005" I took a few times to do this, and I actually over bent it by .012" but I was able to get it back to 0.003"

I am so happy!! I was hoping to get it under 0.010", but 0.003" is awesome!
I almost hope the other fork is bent!! (JK)
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Re: DIY: How to straighten Forks

Postby 97catintenn » Mon Dec 01, 2008 6:32 pm

I take it that the old woodsman method didn't work?

Sometimes, it takes two hands...

Image
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Re: DIY: How to straighten Forks

Postby tristanbadger » Mon Dec 01, 2008 6:37 pm

Maybe Franko just didn't have the required orange cat handy? :dunno

I had mine fixed by a shop, and they used a hydraulic ram but the principles are the same - find the problem spot and overbend so that the at-rest position is straight.

Big kudos for putting together a rig to get this done yourself. I'd considered it the realm of the professionals, but obviously with a bit of thought and some clever engineering, you've managed to get it done very well.

Thanks for the pics and how-to. Superb! :ok

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Re: DIY: How to straighten Forks

Postby Franko » Tue Dec 02, 2008 1:17 am

97catintenn wrote:I take it that the old woodsman method didn't work?

Tell me more about this method... Do I need to buy a cat??? :)
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Re: DIY: How to straighten Forks

Postby midlife_crisis » Wed Dec 03, 2008 7:29 am

Franko wrote:
97catintenn wrote:I take it that the old woodsman method didn't work?

Tell me more about this method... Do I need to buy a cat??? :)
That particular cat is not for sale, but the local pound (where he used to live) usually has several. :angel He insists on helping on just about any job I undertake. As you can see, he got bored with the low-tech low-accuracy handlebar straightening process. :p

Of course, the fork tube was the tool in that process. :lol

Great fork tube how-to, though. I love that stuff. :ok
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Re: DIY: How to straighten Forks

Postby Riceburner » Thu Dec 04, 2008 4:55 pm

Good on ya Frank. With the new front end the Viffer will stop like a Cat.

Thanks for adding to the knowledge base here.
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Re: DIY: How to straighten Forks

Postby thesnowgod » Thu Dec 04, 2008 7:37 pm

Very nice work. Added to Master list!
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Re: DIY: How to straighten Forks

Postby Franko » Sun Dec 07, 2008 11:59 pm

The second fork tube was bent .024".
I put it in the jig and deflected it .212" against the bend for 1 minute.
That left me with .006"... I am happy with that and I polished the tube, and put it together.

Either this is easy to do, or I am really, really lucky. :)
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