GM 12586532 Camshaft, Intake (Machining)

A special camshaft holding tool (GM# J-44221 or equivalent) is required for this procedure. After removing the cam sprocket, do not rotate the crankshaft to avoid incorrect timing and potential engine damage. Begin by removing the valve cover and the spark plugs to facilitate engine rotation. Rotate the engine until the sprocket alignment marks are aligned with a dark chain link, ensuring the nats at the rear of the camshafts are facing up. Remove the camshaft sprocket bolts and carefully detach the sprockets from the camshafts, taking care not to remove them from the chain and suspending them to prevent the chain from coming off the crankshaft sprocket. Check the camshaft caps for markings and mark them with paint if necessary before removal. Remove the camshaft cap bolts gradually until they can be taken out, then extract the camshafts, keeping them separated to avoid mixing them up. The rocker arms and lash adjusters can be lifted out if needed, and these parts should be laid out in order for reinstallation. After cleaning the camshafts, inspect each for scored journals, heat discoloration, score marks, chipped areas, pitting, uneven wear, damaged locator pin slots, and damaged threads. Measure the bearing journals with a micrometer to check for excessive wear or out-of-round conditions. Compare the camshaft lobe heights by measuring each lobe with a micrometer, recording the measurements for both intake and exhaust lobes separately; if the difference exceeds 0.005 inch, the camshaft should be replaced. If removed, soak the lash adjusters and rocker arms in clean engine oil before reinstalling them in their original locations. Coat the camshaft with clean engine oil and place it in the correct position in the cylinder head, then install the camshaft holding tool. Install all camshaft caps in their original locations and hand tighten them, then evenly tighten the caps to the specified torque, working from the center out. Remove the holding fixture, place the sprockets onto the camshafts, and tighten the bolts to the specified torque. Using a large breaker bar and socket on the crankshaft pulley bolt, rotate the crankshaft 720 degrees and re-check the sprocket and chain alignment, ensuring the darkened links align with the sprocket marks; if resistance is felt while turning the crankshaft, stop immediately to diagnose the issue. Finally, install the spark plugs and the valve cover.

Remove the camshaft cap bolts gradually until they can be taken out.

Clean the lifters thoroughly and check for wear, ensuring the rollers turn freely without excessive play. Used roller lifters cannot be reinstalled with a new camshaft, so always use new lifters with a new camshaft.

If the lobe lift is 0.02 inches less than specified, cam lobe wear has occurred, necessitating a new camshaft.