Timing belts are typically only used on overhead camshaft engines. Timing belts are used to synchronize the crankshaft with the camshaft, similar to a timing chain on an overhead valve (pushrod) engine. Unlike a timing belt, a timing chain will normally last the life of the engine without needing service or replacement. Timing belts use raised teeth to mesh with sprockets to operate the valvetrain of an overhead camshaft engine.
Whenever a vehicle with an unknown service history comes into your repair facility or is recently purchased, here are some points that should be asked to help prevent costly engine damage:
Engines, chain-or belt-driven, can be classified as either free-running or interference, depending on what would happen if the piston-to-valve timing were disrupted. A free-running engine is designed with enough clearance between the pistons and valves to allow the crankshaft to rotate (pistons still moving) while the camshaft stays in one position (several valves fully open). If this condition occurs normally, no internal engine damage will result. In an interference engine, there is not enough clearance between the pistons and valves to allow the crankshaft to turn without the camshaft being in time.
An interference engine can suffer extensive internal damage if a timing belt fails. The piston design does not allow clearance for the valve to be fully open and the piston to be at the top of its stroke. If the belt fails, the piston will collide with the valve and will bend or break the valve, damage the piston, and/or bend a connecting rod. When this type of failure occurs, the engine will need to be replaced or disassembled for further internal inspection; either choice costing many times that of replacing the timing belt.
The average replacement interval for a timing belt is approximately 60,000 miles (96,000km). If, however, the timing belt is inspected earlier or more frequently than suggested, and shows signs of wear or defects, the belt should be replaced at that time.
Inspect both sides of the timing belt. Replace the belt with a new one if any of the following conditions exist:
If none of these conditions exist, the belt does not need replacement unless it is at the recommended interval. The belt MUST be replaced at the recommended interval.
Removal & Installation
- Remove all necessary components for access to the upper and lower timing belt outside covers, then remove the covers.
- Align the camshaft timing belt pulley with its timing marks. The crankshaft and camshaft marks are straight up.
- Remove the resonator and the timing belt outside cover.
- Remove the tensioner stud and loosen the tensioner bolt.
Remove the tensioner spring and damper, then remove the timing belt.
WARNINGAfter the timing belt is removed never turn the camshaft or the crankshaft. Interference may occur between the pistons and the valves causing component damage.
- Remove the tensioner and the tensioner plate.
Install the timing belt tensioner plate and tensioner. Only hand-tighten the tensioner bolt.
NOTEBe sure that the lug on the tensioner plate is inserted into the hole on the tensioner.
- Be sure the tensioner plate and the tensioner move uniformly. If they do not move together remove the tensioner and the tensioner plate and reinsert the plate lug into the tensioner hole.
- Check the camshaft sprocket to verify that it has not moved.
- Check the crankshaft alignment by verifying that the punch mark on the timing belt pulley is aligned with the arrow on the oil pump case.
Remove the cylinder head cover.
NOTEThis is to permit the free rotation of the camshaft. When installing the timing belt on the pulleys, the tensioner spring force should correctly tension the belt. If the camshaft does not rotate freely the belt will not be correctly tensioned.
- With the timing marks aligned, hold the tensioner plate up by hand and install the timing belt on the pulleys so there is no slack on the drive side of the belt.
- Turn the crankshaft 2 rotations clockwise. Confirm that the timing marks are still properly aligned.
- If the belt is free of slack and the alignment marks are correct tighten the tensioner stud to 84-96 inch lbs. (9-12 Nm). Tighten the tensioner bolt to 17-21 ft. lbs. (24-30 Nm).
- Install the timing belt upper and lower outside covers. Tighten the timing cover bolts to 84-96 inch lbs. (9-12 Nm).
Install all remaining components in the reverse order of the removal procedure.
- Remove all necessary components for access to the timing belt covers, then remove the covers.
Loosen but do not remove the tensioner bolt.
CAUTIONAfter the timing belt is removed, never turn the camshaft and crankshaft independently. This engine is an interference engine and if the camshaft or crankshaft is turned beyond a certain point, damage to the valves could occur.
- Loosen the timing belt tensioner adjusting bolt and pivot nut. Apply pressure to the tensioner to loosen the timing belt, and remove the timing belt from the camshaft and crankshaft sprockets.
- Remove the timing belt tensioner, tensioner plate and tensioner spring.
- Install the timing belt tensioner, plate and spring. Hand-tighten the tensioner bolt and stud only at this time.
- Turn the camshaft sprocket clockwise and align the timing marks.
- Turn the crankshaft clockwise, using a 17mm wrench to crank the timing belt sprocket bolt.
- Align the punch mark on the timing belt sprocket with the arrow mark on the oil pump.
- With the timing marks aligned, remove any slack from the drive side of the belt. Tighten the tensioner bolt to 16-20 ft. lbs. (22-28 Nm).
- To allow the belt to be free of any slack, turn the crankshaft clockwise 2 full rotations. Confirm that the timing marks are aligned.
- Install the timing cover and tighten the bolts to 84-96 inch lbs. (9-12 Nm).
- Install all remaining components in the reverse order of the removal procedure.