GM 390300 Bearing

Examine the bearing surfaces and the cam lobes; shallow surface scratches can be removed with fine emery cloth or an oil stone, while deep scoring requires a new camshaft. Mount the camshaft on V-blocks and use a dial gauge to measure lobe lift and run-out, rejecting any camshaft that does not meet specified limits. Measure the journal diameters with a micrometer and reject any camshaft that does not meet the specified limits. Worn bearings can be extracted using a suitable tool, such as GM tool set No. J-6098, and it is necessary to drive out the camshaft rear plug from the block. New bearings are installed with the same tool set, ensuring the cam bearing oil holes are aligned: for Small V8, the No.1 bearing hole should have oil holes equidistant from the 6 o'clock position, with No. 2 through No. 4 positioned at 5 o'clock, and the No. 5 bearing oil hole at 12 o'clock; for Mark IV VB, the No.1 through No. 4 oil holes must align with the cam bearing bore oil holes, while the No. 5 bearing bore should be at or near the 6 o'clock position. After installing new bearings, a new camshaft rear plug should be installed flush 1/32 inch below and parallel to the rear surface of the block.