GMC 12638172 Camshaft,Intake

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The camshaft bearing caps are marked with numbers and letters, with a raised arrow indicating the front of the engine. This procedure requires special tools, such as timing chain holding tools (EN 48383-2 and EN 48383-3), to be used; otherwise, you have to remove the timing chain cover in order to properly attach the chain to the lower sprockets. Disconnect battery cable first. Then remove valve covers, power steering fluid reservoir, lower intake manifold for 2008 and earlier models, Camshaft Position (CMP) sensors, camshaft position actuator solenoid valves, and high pressure fuel pump for 2009 and later models if working on left side camshafts. Rotate the engine until flats on camshafts face up. Loosen actuator bolts while holding camshafts with wrench checking end play of the camshaft. Securely install timing chain holding tool (EN 48313) at appropriate points so that it securely holds the timing gears in place then remove camshaft actuator bolts and separate actuators from them. Put these caps into a named box and unscrew their bolts gradually but in reverse sequence following tightening pattern. Inspect all camshafts for wear and measure all bearing journals and lobes. Clean and inspect block's bearings for the cams. Lubricate camshaft properly while positioning it correctly during installation and tightening cap bolts in proper sequence is necessary as well. Do this same thing with other cylinder head cams. Finally, do everything listed above backwards only now changing oil; install new oil filter before starting engine.

Begin by disconnecting the battery cable, removing the valve covers, power steering fluid reservoir, lower intake manifold (for 2008 and earlier models), Camshaft Position (CMP) sensors, camshaft position actuator solenoid valves, and, for 2009 and later models, the high-pressure fuel pump (if working on the left side camshafts).