The 1AZ engine has higher efficiency and fuel economy, low noise and vibration levels, lightweight and compact design, and excellent reliability compared to the predecessor. The exhaust manifold and catalytic converter is one unit. Each fuel injectors has twelve small injection holes (0.18 mm or 0.01 in). The engine equipped with the sequentially injected fuel system. Valve lift is 8.0 mm (0.3-in) for both valve types. Intake valve diameter is 34.0 mm (1.3 in), and for exhaust valve - 29.5 mm (1.2 in). The angle between intake valves and exhaust valves is 27.5 deg. A single-stage roller timing chain drives camshafts. The intake camshaft is equipped with VVT-i system (Toyota variable valve timing system), altering timing by 50 deg. On top of the block, there is aluminum DOHC 16-valve cylinder head. Helical gears are made from polymeric material for the reduction of noise. The applying of balancing shafts was a big step in the reduction of engine vibration. Between first and second bearings there is a gear driven two balancing shafts in the lower aluminum crankcase. The crankshaft is attached to the block by five main bearings. The engine got the forged steel crankshaft, fully balanced by eight counterweights. It features offset cylinder and crank centers. The 1AZ has aluminum cylinder block with cast iron liners.
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