Custom Fighters - Custom Streetfighter Motorcycle Forum banner
1 - 4 of 4 Posts

·
Registered
Joined
·
72 Posts
Discussion Starter · #1 ·
Just a quick one, a mini project if you will.

First thing I did was knock up a big lever press, just using junk I have stashed away for just such days :lol:


You can see it is opened right over itself in this pic, the lever travels through 180 degrees ( and then some more) to allow the pushing block right out of the way of the fork leg, with out the need to hold it off the leg.

Its worth noting rawl bolts are your friend and this will need fastening down.

There is a V block at either end of the steel bed, I made these out of thick wood, but steel would be better - i didnt have and suitable steel so went with wood.



A magnetic based dial indicator is set up on the leg and the leg turned 360 degrees to find the high spot, I took about 5 measurements down each leg length to find the "middle" of the bend. The middle of the bend is positioned directly under the pushing block with the high spot facing up.



The block lowered onto fork, only move the dial indicator as little as possible and zero it, it wants to be as close to the bend as possible and still able to read the fork leg.



Now you push like mad and hope you've made your lever long enough!

I counted the dial round as I pushed by leaning over it, but it would be a lot easier if an assistant could read them out to you!

When measuring the run-out, you turn the fork leg until the indicator is at its highest reading, take a note then turn to its lowest reading and take a note. The run out is half the difference between the two:
Example

Indicator reads 0.10mm and 0.78mm you have a difference of 0.68mm - the total run out would be 0.34mm

This is why its easier to zero your indicator each time.

I started by bending an equal amount in the opposite direction. I had approx 0.8mm of runout so I pushed the leg 0.8mm the other way.
This made NO DIFFERENCE

SO i went to 1.6mm NO difference...

I just kept increasing by 1 mm until i could measure the bend as being reduced. This didnt happen until I had applied 7.5mm of travel in the opposite direction of the bend! And i still had some to go!

In the end I think I applied around 8.4mm travel against the bend, but I am unsure how much of this is due to the wooden V blocks ( they will compress under strain ) and how much is the natural "spring" of the tube - so go careful and ALWAYS measure twice.

When the bend is almost out, you will have to move the pushing block right out of the way and measure right at the arc of the bend to check run out.

When you think your finished, transfer the V-blocks, leg and dial indicator to a known flat surface ( kitchen worktop etc) and re-measure the leg, I took a good 5 or 6 around the bent area, a measurement each end and a couple in between.

Your run-out is always the highest one, if you have 0.5mm run out in the middle and 0.01mm near the end the run-out is 0.5mm

Both of my stanchions were bent, I got one to 0.05 -0.06 ish mm and the other is about 0.03mm

** DISCLAIMER This post is for information purposes only, professional services are advised.
If you follow ANY information in this post it YOUR responsibility to check its safe and ride-able.
I did it to see if it could be done - I am not guaranteeing it is safe for use afterwards
 

·
Administrator
Joined
·
50,498 Posts
very inventive mate ,I can forsee other uses fer that wee contraption .
 
G

·
Nicely done fella, I have done similar using a hydraulic pipe bender a shimmed former & v blocks on moped forks & found it pretty easy as you can bend it a little at a time with no effort, not sure I'd use my idea on forks from a high powered bike though as I'd always wondering if I got it right
 

·
UnicycleMode
Joined
·
7,580 Posts
:cfrocks:



Reminds me I have a set of bent GSXR1100 RSU's that I deemed "junk" long ago... I think it's time to pull them out of storage and get rid of the slight tweak in the legs and bolt them up to my Bandit. Was half way through a stem swap when I discovered the bend in them sliding the forks back in the bottom triple for a length test for the new stem. Crushed me to have to give up the forks on the project... there is hope yet!
 
1 - 4 of 4 Posts
Top