The powerplant used in Saturn S-Series automobiles was a straight-4 aluminum piston engine produced by Saturn, a subsidiary of General Motors. The engine was only used in the Saturn S-series line of vehicles (SL, SC, SW) from 1991 through 2002. It was available in chain-driven SOHC or DOHC variants. This was an innovative engine for the time using the lost foam casting process for the engine block and cylinder head. Saturn was one of the first to use this casting process in a full-scale high-production environment. Both engine types used the same engine block. Engine block The engine utilized a water-cooled aluminum block. The main bearing caps were made of ductile iron and held in place with two bolts each. The cylinder block bores had interference fit cast iron liners for the piston rings to sit against. The engine block was made from 319.1 aluminum alloy and the liners were made from grey iron. Crankshaft The crankshaft was supported by five main bearings with thrust taken at the middle bearing. 1991 and 1992 engines had a different crankshaft from 1993 and later engines, whose crankshafts had reluctor ring slots advanced ten degrees for easier starting. 1991 to 1998 crankshafts incorporated four counterweights, while those from 1999 to 2002 incorporated eight. Connecting rods and pistons From 1991 to 1998 the connecting rods were forged steel with standard type crank pin bearings. SOHC engines during that period used a dished piston design whereas the twin cam engines used a flat top piston with 2 recesses for the intake valves. Twin cam pistons received several re-designs throughout the production run aimed at reducing oil consumption issues. These included reducing the clearance between the top of the piston and the first compression ring, redesigning the skirts on the pistons and the oiling ports on the bottom of the pistons. For the 1999 model year all pistons were totally redesigned. Both engines used the flat top pistons with 2 valve recesses and featured a new hypereutectic design with coated skirts. Also for 1999 all connecting rods switched to a powder forged design and cracked bearing caps. The piston pins floated in the connecting rod bushings. The pistons were cast aluminum alloy with the piston pins being retained with snap rings. Timing chain The timing chain was hydraulic tensioned and had a ratchet mechanism to keep the chain tight. The timing chain rode on one pivoting