GM 12453171 Camshaft Bearing

After removing the camshaft from the engine, clean it with solvent and dry it, then inspect the bearing journals for uneven wear, pitting, and evidence of seizure; if damaged, both the camshaft and bearings will need replacement. Measure the inside diameter of each camshaft bearing, taking two measurements at each bearing, and subtract the bearing journal diameters from the corresponding bearing inside diameter measurement to obtain the oil clearance; excessive clearance necessitates new bearings. Camshaft bearing replacement requires special tools and expertise, so it is advisable to take the block to an automotive machine shop. Check the camshaft lobes for heat discoloration, score marks, chipped areas, pitting, and uneven wear; if the lobes are in good condition and the lobe lift measurements are as specified, the camshaft can be reused. Good used roller lifters can be reinstalled with a new camshaft, and while the original camshaft can be used if new lifters are installed, it is recommended to replace both together, especially for high-mileage engines. For V6 engines, if the balance shaft is to be removed, the balance shaft gear bolt should be removed before the timing chain to hold the shaft while loosening the bolt. Remove the two bolts and the balance shaft retainer at the front of the block, then use a slide-hammer threaded into the front of the balance shaft to knock it out. Inspect the balance shaft and measure the bearing journal diameters; if measurements exceed specifications, replace the balance shaft, bearing, and bushing as a set. The rear bushing, similar to a camshaft bearing, must be installed by a machine shop with the proper tools and alignment. Inspect the balance shaft drive gear and the balance shaft driven gear for signs of wear, pitting, broken teeth, or rough operation, as both gears are serviced only as a set.