The McCulloch BP-399-T Snowmobile Engine and Its Installation

The BP-399-T and other engines of this family were planned as snowmobile and ATV engines with particular regard to balancing. They show shaking forces of 14-30% of those of conventional designs. Engine balance becomes a major factor, wherein vibrational forces should be considered in two classes: those which are symmetrical about the c.g. and cause translations of the c.g. through space, and those forces which are unsymmetrical and cause the body to rotate or rock. The mechanics of design and development are discussed, along with installation problems.