The reason that the moving engine components (rods, crankshaft and pistons) need to be lubricated is because they move at high speeds with a lot of friction. If the oil doesn’t lubricate these moving parts adequately, they will quickly begin to wear out and cause problems with the engine’s operation. This usually manifests as a loud tapping or knocking noise that indicates worn bearings and loose or misaligned internal components. Another sign that your engine needs a rebuild is if the oil in your engine is contaminated with excessive amounts of sludge. This is waste oil mixed with coolant and thickened by excessive friction.
Before you start the actual rebuild, it’s a good idea to remove all the accessories, wiring and hoses from the engine. Be sure to support the vehicle on jack stands so that it doesn’t move during the disassembly process. Next, carefully remove the battery to prevent electrical accidents during disassembly. Use a clean rag to wipe away any oil and grease residue on the surface of the engine block, then use a micrometer or tape measure to check clearances and tolerances and replace parts that are out of spec. Be careful when working with the crankshaft, as it can be easily damaged by incorrect handling. Apply assembly lube to all critical components before reassembling. Be careful not to skip any steps in the rebuild process, as doing so could damage your engine before it ever starts up. Tighten bolts and nuts to manufacturer specifications and carefully align timing marks before finishing the job.