There are too many variables to consider regarding break-in. Since model engines are hard to burn up, they can be ran at full power with little run time. Some motorcycles can withstand or even benefit from the same treatment, some can't without sticking a piston. Large jetski engines can be raced with little run time if the piston fit is extra loose, otherwise they need a long careful break-in. At the other extreme, an airplane or farm tractor may need to run 100 hours at full power before they settle in.