Three common symptoms of a failing timing belt include rattling noises occurring from the front of the engine, retarded ignition timing and plastic chunks found inside the oil pan. A failing timing belt should be quickly replaced as it can cause the entire engine to fail.
When a rattling noise occurs in front of the engine, the belt may be loose or the timing chain may be coming apart. The hood should be opened and the engine inspected before continuing to use the vehicle.
One of the most common signs of a bad belt is when the engine jumps timing. Also referred to as retarded ignition, the engine's start-up sequence will be off. This occurs when the timing belt skips a tooth on the camshaft due to being too loose or stretched.
The most serious symptom revolves around finding plastic chunks inside the oil pan. The plastic chunks will be from the camshaft gears. The camshaft gears are spun by the timing belt. When the belts skips timing it can break off the camshaft pieces, landing some of them into the oil pan. These pieces can then cause the oil pressure in the engine's bottom end to fall. The loss of oil pressure will lead to engine failure and require the motor to be rebuilt.