Check the bearing surfaces and the surface of the cam lobes; light pitting or scratching may be smoothed with fine emery cloth or an oil stone, but if the camshaft is deeply scored a new one will be necessary. Camshafts should be mounted on V-blocks and employed with a dial gauge to measure camshaft lobes lift and run-out and exclude camshafts that do not meet the stipulated camshaft lobe lift and run-out. Use a micrometer to measure the journal diameters; it is mandatory to scrap any camshaft which does not conform to the above limits. In the case where either camshaft bearings are worn out or in some conditions damaged, then they have to be replaced; it can be done by having to detach the crankshaft but maintaining cylinder heads and pistons. To avoid getting damaged, the connecting rod bolts should be taped before the removal of the crankshaft and the connecting rods should also be taped to the side of the engine to minimize on interference when removing the bearings. Take out the camshaft rear cover from the top of the cylinder block. Bearing can be removed using GM tool part number J-6098 or a like bearing remover / installer tool according to the instructions. The same set of tools is used to set the camshaft bearings where, for instance, the front and the rear bearings help in centering the remainder of the bearings so that the oil hole in the bearings will match the oil hole in the block. Remove any debris, oil or old gasket material from the camshaft rear cover, then give the cover a layer of RTV or any other equivalent sealant with 1/8 in x 3mm diameter around the sealing surface before fixing the cover on the engine block. Finally, reinstall the crankshaft.
