Here's another 'metric' that you can use: the top edge of the top pressure plate of the clutch should be even height with the ends of the clutch basket fingers. The lifter can reach it if it is within +/-0.5mm from dead-equal height, leaving you some adjustment afterward.
his all came about because Honda was sensitive to the magazines of the 1970s complaining about the shifting clutch engagement point of the clutch lever on the CB500-4. the long clutch rod that went thru that engine was steel, while the cases were aluminum alloy: the cases spread about 1mm in width as the engine heats up, while the clutch rod only extended 0.2mm (at 200 degrees F). The result was that the lever had to be adjusted to 0 clearance when cold to get 0.5" (6mm) slack at full temperature. In the CB550, the clutch lifter was grafted into the existing cases and the top pressure plate thickened a little bit, and the disengagement direction was changed to push from the right side instead of from the left, so the total change-for-heat difference at the lever became less than 2mm after warmup. But...this also reduced the available lift distance to less than 5mm total travel because of the shape of the little lifter cam and the lack of space to make it bigger without redesigning major parts of the engine. While it was a clever fix at the time, it does leave the stack height of the clutch as a critical dimension.
All this info is lost to modern vendors, though, as they just sell stuff without doing research on whether it will actually WORK in the bikes. This is much, much different from the Honda community of the last century! We're really fortunate to have this SOHC4 forum so we can get this info out to those who love these bikes as much as we who rode them since 1969.
