Late DOHC engines do not need to remove the timing belt and front oil seal housing to remove the oil pump, just remove the lower oil pan, disconnect the large oil supply pipe, and then remove the oil pump; although the oil pump drive chain would need to be removed first to check. Start by taking out the timing belt and crankshaft sprocker, then the lower oil pan, then the timing belt tensioner, tensioner pulley, tensioner lever and idler pulley. In SOHC engines and early DOHC engines, loosen the oil pump mounting bolts, remembering that the bottom four bolts are reached by removing the lower oil pan opening and then unscrewing the oil pump housing of the front of the engine. In the case of later DOHC engines where the oil pump is driven by a chain, remove the front oil seal housing, oil pump drive chain cover and long oil supply tube making sure that the O-rings remain attached to the tube. Indicate the drive chain and lower sprocker to ensure that they are reinstalled correctly, loosen the bolt on the oil pump sprocker, part the lower drive sprocker and oil pump shaft, and disassemble the oil pump with the short supply tube, including the removal of the O-ring. Detach the drive chain to the upper sprocket and eliminate it, and clean all the parts and check on wear or damage, and when needed, replace it. To install onto SOHC and early DOHC engines, clean all mating surfaces, apply RTV sealant, position the oil pump housing gasket and install the oil pump with the lubrication of the oil seal lip to avoid dry starts. Bolts of the oil pump housing are tightened, the rest of the parts are assembled in the same order, including the addition of oil and coolant, starting the engine, and inspecting the oil pressure and leaks, and then rechecking the level of the engine oil. In the case of further DOHC engines, new O-rings are fitted on the short supply tube, the drive chain is engaged around upper sprocket, the oil pump sprocket must be aligned with the drive chain, the retaining bolt is installed, the long supply tube O-rings are replaced and final components are fitted in reverse order, adding oil and coolant, starting the engine and checking oil pressure and leaks and repeating the check on the engine oil level.