So, my CB750 engine is a late K0, mfg date 2/70. Thus, it has the early cam support design with only one bolt holding the rocker arm shaft. Note the undrilled location where bolts are added in the later design.
Here's the later design (this is a K3) - note the additional bolts (not installed in this pic) to lock the rocker shaft in place.
My understanding is that this was done to reduce valve train noise.
Now, it's my understanding that the earlier design has a certain friction advantage over the later design in that the shaft is theoretically free to spin under the rocker arms, however looking closely at my rocker shafts they have a groove cut across them, rather than all the way around as in the later shaft:
Upper: Early Shaft
Lower: Later Shaft
So, the earlier shaft is, in fact, locked in place and will not rotate, which is supported by the wear pattern on the shaft - one can see where there's some work polishing on the shaft from the rocker arm (note, left side of shaft has been polished already).
The later shaft, in addition to being able to rotate freely so long as the additional bolts are not used, also have those extra oiling grooves, which catch and distribute the meager oil that gets delivered to this are via splash oiling. Correct me if I'm wrong, but all the oil that the rocker arms get come from oil landing in the machined holes on the shoulders of the rocker arms. The later shaft's oil grooves align with these so a small resevoir of oil would form here making for better lubrication of the shafts.
So, I'm currently thinking that the way for me to go is to polish up the newer shafts and use them with my older cam holders. No bolts to hold it in place and a full groove to allow the shaft to rotate, plus better oiling to boot.
Sound right?
mystic_1
