Sunday, 3 April 2016

Fitting ZX6R yokes onto XV750-ies and TR1-s

My mate Andreas recently asked me for a favour: He had some 2008 Kawasaki ZX6R forks kicking about and wanted to fit them into his XV750. Naively I was assuming he had done his homework beforehand and chosen a set of yokes that would only include a bearing swap to fit...

 So there you have it: XV750 yokes on the left and ZX6R on the right.
After some careful measuring (with a yard stick) it became pretty apparent that this isn't going to be a case of "just" swapping the stems either. More cunningness, i.e. machinery has to be applied.
 Cut off the lower yoke from the stem and roughly trim it to size. Until you end up with this:

The next logical step was to shorten the original ZX6R yoke so it would go into the press with reasonable effort.


Then it was time to press out the stem on the press (with lots of pre-heat) it started to move at around 15 metric tons, which is a lot more than I have ever seen so far on such a job.

 Subsequently it was necessary to machine down the stoke XV750 yoke to fit into the opening on the ZX6R yokes. At this point I feel obliged to say thank you to Yamaha for using some nicely machineable steel on the lower yoke as it was really nice to turn down on the lathe with a new carbide insert. (TCMT16 in case you're curious or trying to gauge the size of my lathe...)

 Unfortunately the intended press fit became a bit more of a push fit and as such wasn't quite up to the job. Modern adhesives to the rescue: Loctite 638 can bridge 0.25mm gaps and carry loads of up 25N/mm2, which is already somewhere in the vicinity of a not so shabby weld. I turned down an old bolt to fit the stem at exactly the height of the yoke, whilst holding it down with the quill of my mill.

 Just to be on the bolts 'n' braces side, I then went about and tapped a M6-thread through both the lower yoke and approx. half of the stem (didn't want the bolt to fall through) and use a little M6 set-screw to pin it down just to be sure.

When I said, nothing fits with these yokes, I literally mean NOTHING. So the next step was to turn up a spacer ring for the upper yoke, so the stem is located properly.

The end-result is pretty convincing though, except for the stock bolt in the upper yoke it looks as stock as it can. 

A little note for the copy cats: Check the clearance of the lower yoke and don't have the stem sit flush in the yoke, but raise it a bit, otherwise you'll end up trimming the lower bearing cup holder on the frame a bit.

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