A strange one this, but it's why I haven't been able to try my new oil cooler 'sinks' lately. During my XB's recent MOT, the tester spotted some light scoring on the r/h chrome fork slider. Not serious enough for the seal to fail, but worth looking at.
I cleaned the dust seal, which revealed nothing so as a precaution I took the fork leg off to check inside and do a fluid change. While dismantling I noticed that the upper caliper bolt fixing hole housing (say that while drunk) had a crack in it just where the surround narrows (bad design?).
Particular to my XB is that I suspect that there was a minor casting fault around this point from new, but I never looked at it too deeply. The alloy cracked just along the ridge of this. Another thing I observed is that there is a step inside the bolt holes about 2mm from the bottom. The bolt heads seem to be too big to seat on the base and would appear to rest on this step. Can that be normal?
Whatever, I gave the leg to my friendly local bike engineer who has machined out and alloy-welded the damaged area. His view is that the bolts have been over tightened and he showed me the subtle squashing of the alloy seat against the harder materials, which in turn makes the bolt shafts tighten in the hole over time.
My last assembly of the front end is what did for the r/h fork casting. Mind you I have rarely used the full recommended torque of 35 lbs ft. Could the manual may be wrong or is it my torque wrench.
We looked at some other bikes in the shop with Showa forks. A Ducati 900 Superlight or similar had a plain bolt hole housing with no step inside and more importantly nearer half an inch of alloy surrounding the bolt shaft, unlike the puny looking XB housing. I am left wondering if my XB fork leg was just machined wrong to start with or are all XBs the same? One thing I do know is that my XBs caliper has been on and off the bike many times due to tyre, head bearing, and wheel bearing changes from all the miles I have done over 8 years. Maybe other owners have not experienced this because they change all the above consumables together?
I am now contemplating having the bolt heads narrowed by a very small amount to miss or stop pressing so hard against the step (the local chap has a machine to do this). The bolt holes also need to be reamed out a fraction for the bolts to fit correctly again. I am concerned about seating the bolts on thin alloy hole bases, but equally having the bolts rest on the 1/2mm step or being wedged so tight inside it can only produce adverse outward stress?
Maybe I should have the holes totally welded up to the top and re-drilled and machined, but I don't want to have too much heat put into this casting. I will use minimum torque and locking compound for a change. Has anyone else experienced the same issue?