What is a timing belt?
A timing belt runs between the crankshaft and the camshaft on an overhead cam engine and rotates the camshaft(s) in time with the crankshaft. The belt incorporates cogs that mate with grooved crankshaft and camshaft pulleys. The belt is made from a rubber-like substance and reinforced with fiberglass strands. The timing belt wraps around several smooth idler roller and in some engine designs also drives the engine’s water pump and oil pump. The belt is properly tensioned with a mechanical or hydraulic (oil pressure driven) tensioning device.
Timing belt history
In older overhead valve style engines, the camshaft was located near the crankshaft and driven by a set of gears or a chain. However, when engine designers shifted to an overhead cam design, where the camshaft(s) are located quite a distance from the crankshaft, they felt a chain would have made too much noise. So they opted for a rubber cogged belt. The first designs were made from neoprene/nitrile saturated rubber with fiberglass reinforcement strands. Unfortunately, neoprene is susceptible to damage from heat and oil, both common in an engine. So the early engine versions required timing belt replacement as often as every 60,000 miles. Replacing a timing belt is a labor intensive job and can easily run upwards of $600 to $800. Consumers complained about the high maintenance costs associated with timing belts. Manufacturers responded by changing the design of the timing system and began incorporating more resilient rubber compounds. That increased the life of the belt to 90,000 to 110,000 miles. However, some car makers developed low noise chain-driven overhead cam engines. When properly maintained with regular oil changes, a timing chain can last the life of the vehicle. Under pressure to reduce maintenance costs, many car makers moved to timing chains in the early 2000’s.
Why is it so important to change a timing belt on time?
A timing belt cracks as it wears and cogs can break off the belt. Those missing cogs can cause the crankshaft and camshaft to rotate out of time, and on some “interference engines, can cause catastrophic engine damage as the pistons and valves collide. A broken timing belt can leave you stranded and, depending on engine design, can literally destroy your engine, costing $2,500 to $4,000 to repair.
Posted on by Rick Muscoplat