One tip for adjusting the timing of a GM engine is to avoid cranking the engine or rotating the cam or crankshaft on interference engines suffering from a broken timing belt. Another tip when working on engines that utilize a timing chain is to replace the crankshaft and camshaft sprockets along with the chain. Three of these components wear as a system and should be replaced as a set.
Many GM Interference engines do not have enough clearance between pistons and valves, and cranking an engine that has suffered from a damaged or broken timing belt may cause further damage. When working with an interference engine, pull the head, and inspect valves and pistons before replacing the timing belt.
The timing mechanism is the system which causes the spark plugs to fire once pistons and valves are in the correct position. The basic process for setting and adjusting the timing are basically the same for most types of engines, although newer vehicles typically employ self-adjusting ignition systems that do not require timing adjustments. Recommended intervals for timing adjustments may vary depending on a vehicle's make and model. Always consult the owner's manual before attempting to adjust ignition timing. Replace timing belts and chains according to the manufacturer's recommendation, or should they be suffering from visible signs of wear and stress.