Timing Chains and Timing Belts

The timing chain or timing belt connects the crankshaft to the camshaft and keeps them perfectly synchronized. This is one of the most critical components in the engine because if the timing relationship between the crankshaft and camshaft is lost, the valves and pistons can collide and destroy the engine internally.

Timing chains are metal roller chains similar to a heavy-duty bicycle chain. They are durable and typically last the life of the engine if oil changes are maintained. However, they do stretch over time as the chain links and pins wear. A stretched timing chain retards cam timing — the camshaft falls slightly behind where it should be relative to the crankshaft. Symptoms include a rattle from the front of the engine at startup, reduced power, poor fuel economy, and timing-related fault codes. Chain-driven engines also have chain tensioners — either hydraulic or spring-loaded — that keep the chain tight. A failed tensioner allows the chain to slap and can cause the chain to jump teeth.

Timing belts are reinforced rubber belts with teeth that mesh with sprockets on the crankshaft and camshaft. They are lighter and quieter than chains but they wear out and must be replaced at the manufacturer's specified interval — typically 60,000 to 105,000 miles. This is not a suggestion. A timing belt that breaks while the engine is running causes immediate loss of power steering and power brakes — the vehicle becomes very difficult to control.