Complex sentence: These transverse forces are tolerable in a smaller engine; a larger engine's much greater forces would cause an intolerable degree of wear on the piston and cylinder, as well as increasing overall friction in the engine.
Split into simpler sentences: These transverse forces are tolerable in a smaller engine. A larger engine's much greater forces would cause an intolerable degree of wear on the piston and cylinder, as well as increasing overall friction in the engine.