The engine is a compact, inline 4-cylinder powerplant. The engine block is a special cast iron alloy: the cylinder head and timing case cover are aluminum alloy. The engine is undersquare i.e., the stroke is larger than the bore. With this design, the surface area-to-volume ratio is smaller, which helps minimize hydrocarbons emissions. Five main bearings support the forged steel crankshaft. Forged connecting rods attach the aluminum pistons to the crankshaft. Full floating piston pins are used and are offset on the thrust side to minimize piston slap. Later model engines, in the United States, have the MCA-Jet system which allows better combustion (less emissions) and improved fuel economy through the use of a jet valve in each of the cylinders (see for details).
The overhead camshaft is driven (depending on the year or engine) by the crank through a double-row, roller chain or a cogged rubber timing belt. The cam runs in five bearings (three on the 1410 and 1468cc engines) and operates directly on the rocker arms. Intake and exhaust rockers are mounted on separate shafts. Rockers act directly on the valves, which open and close in a hemispherical combustion chamber formed by a domed combustion chamber and a flat topped piston. The cylinder head is a cross-flow design. The carburetor feeds into the intake manifold on one side of the engine and the exhaust gases are exited through the exhaust manifold on the opposite side of the engine. This design permits much more efficient cylinder head porting (breathing).
A silent shaft engine is also offered. The silent shaft engine incorporates two chain or belt driven counterbalance shafts mounted in the cylinder block. The counterbalance shafts rotate at twice crankshaft speed and in opposite directions to balance out the usual vibration associated with a 4-cylinder engine.