Timing is Everything

Real world experience: A mini-truck was cruising a rural road. The engine died mid-shift. One minute it was purring right along, the next minute the only sound was the wind whistling in the open window. Turn on the ignition and nothing, absolutely nothing.

Time's Up
After the truck was dragged to a mechanic, the diagnosis: The timing belt broke; the truck was lucky it occurred with the tranny disengaged or the engine may have received terminal damage. So, what's all the fuss about the timing belt? How could its demise wreak such havoc on the engine and what can be done to avoid this unfortunate automotive surprise?


For those who skipped auto shop class, the timing belt is a nylon-reinforced rubber serpentine belt with square teeth on the inside surface. Its function is to transfer the rotation of the engine crankshaft to the camshaft-the component that moves the piston valves up and down.


Even the non-mechanically minded know the valves admit air and fuel and expel exhaust gases; without functioning valves, your engine is dead in the water. The timing belt, true to its name, governs the precise timing of the opening and closing of the cylinder's valves. By controlling the ignition of the fuel/air mixture, it secondarily controls the motion of the pistons. Unfortunately in the case of a broken belt, the pistons will complete their cycle even with inert valves.

Damage Control
To understand the degree of damage, let's take a quick refresher course in Auto 101 (or at least the class you skipped). When the piston is at the bottom of its travel, the valves are open; as the piston hits its high point, the valves are closed.