GM 12453171 Bearing,Camshaft

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It is important to keep the valve lifters and pushrods in order during the removal and installation of the 4.5L and 4.9L engines.

To determine the extent of cam lobe wear, check the lobe lift before removing the camshaft. Position the number one piston at TDC on the compression stroke. Loosen the rocker arm nuts and pivot the rocker arms sideways. Mount a dial indicator on the engine and position the plunger against the top of the first pushrod. Zero the dial indicator and slowly turn the crankshaft in the normal direction of rotation until the indicator needle stops and begins to move in the opposite direction. Record this figure and repeat the check for each valve. If the cam lobe lift is less than specified, install a new camshaft. Remove the camshaft and remove the intake manifold, rocker arms, pushrods, timing chain, and camshaft sprocket. Remove the balancer shaft drive and driven gears if applicable. Pull the camshaft out carefully, supporting it near the block. After removing the camshaft, inspect the bearing journals for wear and damage. Measure the bearing journals with a micrometer to check for excessive wear or out-of-round conditions. Check the camshaft lobes for discoloration, score marks, chipped areas, and uneven wear. Clean the lash adjusters and check for scuffing, score marks, and uneven wear. If the lash adjusters are worn or damaged, replace them along with the camshaft. For roller lash adjusters, check the rollers for wear and damage. Lubricate the camshaft bearing journals and lobes with moly-base grease or engine assembly lube. Slide the camshaft into the engine, being careful not to scrape or nick the bearings. Install the balancer shaft drive and driven gears if applicable. Install the timing chain and sprockets. Lubricate the lash adjusters with clean engine oil and install them in the block. Finally, change the oil and install a new oil filter before starting and running the engine.

To remove the camshaft, you should first remove the intake manifold, rocker arms, pushrods, timing chain, and camshaft sprocket. If applicable, also remove the balancer shaft drive and driven gears. Carefully pull the camshaft out, supporting it near the engine block.