The thing that goes through my mind with this is the pulsating nature of the load imposed upon any bearing inside the camshaft. The total mass to be moved in the valve train for any one valve is about half a kilo. The maximum acceleration imposed by the cam profile is about 200 G. But the situation on the cam shaft is somewhat worse due to the lever nature of the cam follower which can increase the loading by a factor of about two. So at 6,000 rpm the cam end of the cam spindles can be subject to a fluctuating load of about 200 kg. Clearly needle rollers have been used so that they will stand this hammering for some time. As for longevity then it might be a case of "come back Oilite, all is forgiven". I would like to see a long term road test before I ceased to worry about the lifetime of needle rollers in this application.