They say that imitation is the sincerest form of flattery, in this case it is copying but I hope Daywalker is still flattered.
Whilst flicking through Performance Bikes one month, reading about how great all the Jap and I-tie stuff was (again), Son of Grenade commented on how tidy radial calipers looked and it was this that sowed the seed in my mind.
Daywalker had told me about his plans for grafting a GSXR front end onto his S1 (or maybe S3) some time ago, and had posted about it
here and had been busied for some time pulling all the bits together. I was also interested to read that
OF had done the same, so you could say I am copying him too, however my installation is a little different to retain the Buell (fork) trail.
Daywalker pointed me in the direction of a complete front end minus wheel and fender (cue clip round the ear from my dad - I really meant mudguard...) from a 2007 GSXR 600 K6/K7, after lots of umm-ing and arr-ing and a few glasses of wine in a restaurant in Menorca, I clicked the Buy-It-Now button.
They came with calipers, a top yoke, clip ons and all controls, however the sliders were pitted and with the help of BeGay and the passing of two months I managed to get another set of sliders. This enabled me to strip and rebuild the forks (with some of my RC30 fork seals - yes the GSXR, RC30 and X1 share the same fork seals).
The forks are 53mm diameter at the bottom yoke (1mm smaller than the X1 Showas), 50mm at the top yoke (4mm smaller than X1 Showas) and a 41mm slider diameter (same as the X1 Showas). More importantly, they are the same length as the X1 Showas. Plenty of details
here, some dimensions are better measured yourself, for example, as we will see later, the centreline of the gap in the calipers.
The yokes from the GSXR look OK on a GSXR, but I wanted to retain the bars and mount for the clocks, so Keeper of Stumpy helped me out with some M2 yokes which I thought I would bore out to fit the new stanchions.
The M2 yokes have 43mm holes and they are the same forgings as the S1 and X1 which have 54mm holes, so an ideal starting point for a new set of forks of smaller diameter stanchions.
I already had a set of made to measure 320mm EBC Pro-Lites with Buell PCD from another concept I was planning to use, and currently in use on another forum member's bike.
I chose 320 as the standard 340s are just too much, unnecessary mechanical advantage, unnecessary inertia, unnecessary gyro effects and makes it a pain in the arse to get the the front wheel off. In hindsight, I should have chosen 310mm discs as that is what the GSXR donor bike uses.
My plan was to use these discs with the Buell front wheel (I want to keep it Buell as much as I can - besides I have a posh front wheel), so the design objective was to get the (radial) calipers to line up with the discs.
The disc to disc centreline on my front wheel was measured as 124.2mm, the gap to gap centreline between brake calipers on the GSXR forks was measured as 130.5mm. This meant that to mate the GSXR forks with the Buell wheel, the GSXR fork centres needed to be reduced by the difference, from 206.3mm to 200mm. Comparing that to the Buell centres of 195mm told me I needed to bore the M2 yokes 2.5mm off centre. With the GSXR stanchion 53mm in diameter at the bottom, compared to the Buell stanchion 54mm (5mm loss in radius), this meant I would be eating 2mm into the meat at the edge of the yoke which seemed a little much.
The calipers themselves give a 2mm clearance either side of the disc. I have decided to eat 1mm into that clearance by bringing the caliper in a further 1mm, the change in bore centre reducing to 1.5mm. This means I am only eating into the yoke material 1mm.
The top yoke is not a problem, the stanchions are 50mm diameter there, way under the 54mm of the Buell stanchions, and hence a 1mm change in centre line of the bore still has an extra 1mm margin over the S1/X1 yoke.
A quick chat with the legend that is my old man to reserve his Bridgeport milling machine yielded the question, 'Are the stanchions parallel to the steerer tube?', something I had not considered, but a check was performed using a bottom yoke with the steerer tube removed (this was swapped with Daywalker for a fried breakfast) and a top yoke whereby all holes lined up (they are all the same size 2x43mm for the stanchions and 1x1" for the steerer tube), I also PMed Spondon440 to confirm.
I bored the yokes...
Then did a trial fit (note the faded stanchions from the California sunshine - I'll get these anodised over the winter)...
The next thing to think about was how to get the big fat 25mm GSXR axle (sorry dad, I meant spindle) to fit the wheel after it had been designed for the 20mm spacer (over the 17mm axle). Well easy, just needed to swap the 6204 bearing out for a 6005 (same as XB), fashion a new inter bearing spacer up from a bit of 25mm ID 6082T6 tube from EBay and fashioned up some spacers to centre the wheel. The bearing size will obviously put me in the same position as the XB front wheel with regards to bearing life but I can live with that. The spindle is still a little long and needs about 6.3mm to be cut off the end.
Next job was to strip and rebuild the calipers:
Always worth doing cos you never know what gunge you will find...
As I said earlier, the calipers and yokes are there to service 310mm discs, cue new spacers:
The next challenge was how to make the headlamp brackets fit... I made up some top hat sleeves for the 50mm and 48mm diameters on the fork stanchions from some more EBay 6082T6.
*** PICTURE TO FOLLOW ***
Then I screwed it all together...
Yet to try it as Albert is busy beavering away making my new exhaust system....
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