the S engine family, manufactured by Toyota and designed in conjunction with Yamaha. While the block is iron, the cylinder head is made of aluminium alloy. The pent-roof combustion chambers are complemented by a cross-flow intake and exhaust layout. The spark plug is located in the center of the combustion chamber. The firing order is 1-3-4-2, with cylinder number 1 adjacent to the timing belt. The 3S-GE was designed to be light, the first iteration 3S-GELU weighing in at a low . The forged crankshaft, located within the crankcase, rotates on five aluminium alloy bearings and is balanced by eight weights. Oil holes are located in the middle of the crankshaft to provide oil to the connecting rods, bearing, pistons and other moving components. The intake manifold has four independent ports and benefits from inertia build up to improve engine torque at low and medium speeds. A single timing belt drives the intake and exhaust camshaft. The cam journals are supported on five points between the valve lifters of each cylinder and on the front of the cylinder head, and are lubricated by an oiler port located in the middle of the camshaft. The pistons are made from an aluminium alloy, designed to withstand high temperatures. An indentation is incorporated into the piston head to prevent the pistons from hitting the valves, should the timing belt break (this is not true of the later BEAMS - an acronym which stands for Breakthrough Engine with Advanced Mechanism System - motors). This is commonly referred to as a "non-interference" engine. Piston pins holding the pistons in place are locked by snap rings. The "Outer Shim Type System" allows for the replacement of the shims without the need to remove the camshaft. To adjust the valve clearance, adjust the shims above the valve lifters. The first compression ring and the oil ring are made of steel, the second compression ring is made of cast iron. Compression rings 1 and 2 prevent exhaust leakage from the combustion chamber while the oil ring works to clear oil off the cylinder walls, preventing excessive oil from entering the combustion chamber. An oil pan baffle is used to ensure that there is sufficient oil available in the oil pan. There are five generations of the 3S-GE, which were used in the Toyota Celica, Toyota Corona, MR2, Caldina, RAV4, and Altezza. All 3S-GE engines had a displacement of