Richard; lots of work when the original cam end bearings work very well to over 8 thousand RPM’s. It’s the oil pump not getting oil to the cam that causes the problems. Miles Chappell made a cold rolled steel oil pump rod and I had the eccentric on the hub running the oil pump. I is a bullet proof upgrade that will work on every N or Z 600 oil pump. Sleeve the hub and wear is removed, and steel rod (shown in the second pic) will never break. But even if you Line Bore https://ceomachining.com/what-is-line-boring/
and put bearings in the
cam box ends will not stop catastrophic damaged caused by lack of oil to the cam box.
Bill