Quote Originally Posted by jmg8550 View Post
Also wondering if motorcycles need oil with zinc to help protect the bearings. Modern oils don't have the zinc additives, and older engines need it or the bearings will be destroyed.
The zinc is needed to prevent gear teeth from galling in bikes that use a shared oil supply between engine and transmission (most modern bikes). Diesel oils work well in most applications, but have reduced shear resistance at very high rpm compared to engineered motorcycle specific oils, leading to more rapid viscosity loss at elevated rpm (over 10000 or so).