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Old 07-18-2011, 08:20 AM   #42
ontic OP
Joined: Jul 2008
Location: Melbourne
Oddometer: 1,070
front end update,

Finally, this morning, my 320mm rotor arrived from Germany so this afternoon I was able to begin figuring out an adapter bracket.
Now, I have read in quite a few places that with these forks there are problems when one attempts to fit a 320mm rotor on a 21 inch wheel.
As far as I could find out there was no stock part (ie caliper bracket) to do this, and I had also read of interference between the rotor and the wheel, with fabbing required and even grinding the back of the caliper?
anyway, what the hell, I wanted a big rotor so I thought I would give it a go.

What I ended up scoring on ebay (for very little) was a caliper bracket for a 21 inch rotor from a slightly later KTM that had USD forks yet still took the same brembo two pot caliper.
So, it would fit my caliper, but of course having a different bolt spacing it would not fit my fork lower properly. I had no idea what would be required to make it work, or if it would work, but it seemed worth a try.

Here is this later 320mm caliper bracket bolted up with the new rotor in place positioning the caliper in the best possible position... head scratching time.

Originally I was planning on measuring up and making from scratch some kind of relocator bracket to reposition the caliper and its bracket into a good position for the rotor. Then, considering how close to ideal position the caliper sat by using the lower hole in this bracket, and looking at my materials at hand, I thought of something else.

I happened to have also bought off ebay another of these same calipers but this time with a bracket for a much smaller rotor, suited again to a later KTM with USD forks- it had the same spacing for the mount to the forks.
I got the idea to use this second caliper bracket on top in what might be described as a rather inelegant solution...
something like this but with the end cut off and a new bolt hole for my upper fork mount

so, with the need for little more than a hacksaw, a grinder and some files and sand paper and drills I set to work.

Off with the end and then I had to do a fare bit of grinding and filing the underside to get it to fit snugly into the shape of the WP extreme fork lower (I did not want to muck around with the fork lower itself at all)

after a few hours of fiddling and fettling I got it together in a solution that may not look all that great but is very solid (possibly stronger than stock) and really quite simple.
That top bolt is spaced/shimmed between the brackets with an odd collection of bits that I will probably be replaced with a one peice sleeve.

here you can sort of see the position of the pads on the rotor.
this is the lower end of the pads- as can be seen the pads go right to the edge of the rotor

the top edge of the pads I have swung in a bit further to spread the load a bit wider over the rotor. It does not seem posible to get this caliper (with or without the bracket) deep enough onto the rotor to use all of the intended braking surface. I doubt this will be a problem but welcome any comments about this.

This is really as deep as I could get them onto the rotor without modifying the caliper- and even this took a little bit of filing on the caliper bracket in the rotor slot to get the most out of it,
all hard to explain and I don't have good pictures to do it for me.
If anyone is interested in the specifics just ask,

finally the comparison
old verses newer

All up I am not sure if it is 'interesting' or just plain fugly!

Whatever the case it feels like I could belt it with a BFH and it wouldn't go anywhere.

Next is just waiting for the new triples... unless I get impatient and decide to try this out by modifying the current KTM triples to fit.
1974 R90/6
1981 R80G/S
1994 XLR250R
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