GM 12640448 Oil Pump

Remove the timing chains. After noting the installed position, remove the timing chain sprocket from the crankshaft. Remove the oil pump retaining bolts and slide the pump off the end of the crankshaft (Oil pump retaining bolts). Remove the timing chain guide from the oil pump housing then remove the oil pump cover and withdraw the rotors from the pump body. Remove the snap-ring from the side of the pump housing and withdraw the cap, spring and plunger from the oil pump housing. These components are the oil pressure relief valve assembly. Clean the components with solvent, dry them thoroughly and inspect for any obvious damage. Also check the bolt holes for damaged threads and the splined surfaces on the crankshaft sprocket for any apparent damage. If any of the components are scored, scratched or worn, replace the entire oil pump assembly. There are no serviceable parts currently available. If re-using the oil pump, assemble the pressure relief valve components and the rotors to the oil pump housing. Prior to installing the cover, prime the pump by pouring clean motor oil between the rotors. Install the cover and tighten the retaining bolts. Position the oil pump over the end of the crankshaft and align the flats on the crankshaft with the flats on the oil pump drive gear. Make sure the pump is fully seated against the block. Install the oil pump mounting bolts and tighten them to the torque. The remainder of installation is the reverse of removal. Add oil and coolant as necessary. Run the engine and check for oil and coolant leaks. Check the oil pressure.