Examine the bearing surfaces and the surfaces of the cam lobes; surface scratches, if very shallow, can be removed by rubbing with a fine emery cloth or an oilstone, while any deep scoring will necessitate a new camshaft. If the bearings are worn, they can be extracted using a suitable tool, such as GM tool set No. J-6098, which is designed for this purpose, and it will be necessary to drive out the camshaft rear plug from the back. New bearings are installed using the same tool set, ensuring to align the cam bearing oil holes according to the manufacturer's instructions supplied with the installation/removal tool.