You've only solved a problem successfully, when you actually have tried all available ways on how to not solve a problem quite as successfully. This time the grub-screw modification as illustrated on quite a few SR500/XT500 forums. Whilst the solution is technically sound, it will only prevent the rockers shafts from lifting in their bores, but not from spinning, which is the original reason, why the bores wear out.
So let's turn that engine to TDC, remove the oilfeed to the rocker shafts and measure just how far in from the mating surface I drilled those holes last time. (8mm on both) and get those shafts.
Transfer those 8mm onto the shafts and with a new carbide endmill, make a flat on the rocker shaft.
Which brings us to the star of the show: M6x10 grub screw DIN916 (flat tip/no tip) as shown in the top right, which is in contrast to its tipped brethren on the left. Even though in theory the tipped version will be less likely to work itself loose it has no means to prevent the shaft from rotating. Given the not unrealistic concern regarding the grub screw coming loose: bolt adhesive has been invented already.
For the rear screws (yes, two stacked on top of each other) a cheap allen key from a well known furniture house had to be shortened on the long leg.
From a technical point of view, now this 2J4 head has reached the same level of rocker shaft retention as the later 48T mode. From here onwards, wear should only occur between rocker and shaft and judging from what I've heard these thanks to a good material combination and plenty of lubrication should last quite a while, before a replacement is due.
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