1. Engine Service Limits

A. Engines may be rebored to the manufacturer’s first standard overbore, not to exceed 0.020 inch (0.508 mm). Sleeving is allowed to repair to the standard bore. Only OE-type standard or first overbore pistons of the same configuration and of the same or greater weights are permitted. No interchange between cast and forged pistons is allowed.

B. Valve seats and guides in older engines originally designed for leaded fuel may be only substituted with alternate components if the dimensions are the same as those of the standard components.