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 is 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
3.0L (VIN R) Engine
- Before servicing the vehicle, refer to the precautions in the beginning of this section.
Remove or disconnect the following:
Negative battery cable
- Rotate the crankshaft clockwise to 60 degrees before top dead center (BTDC).
- Loosen the timing belt tensioner and idler pulleys.
- Remove the timing belt.
- Start at the crankshaft sprocket and install the timing belt with the double dash (TDC) aligned with the marks on the oil pump and on the belt drive gear.
Set the initial timing belt tension as follows:
- Turn the tensioner nut COUNTERCLOCKWISE to full stop, then, turn the nut back until the reference mark is 1 mm (0.003 in) over the flange.
- Tighten the timing belt tensioner locking nut until snug, the locking nut will be tightened to specifications after all final adjustments are made.
- Rotate the engine in the clockwise direction two revolutions stopping at 60 degrees BTDC.
- Inspect the alignment of the reference marks on the camshaft gears with the notches on the rear timing belt cover, as well as, the mark on the crankshaft sprocket and oil pump housing.
If timing belt adjustment IS NOT required, set the final timing belt tension:
- Loosen the timing belt tensioner locking nut.
- Turn the locking nut counterclockwise to full stop, then back until the reference mark is 2-4 mm (0.078-0.157 in) ABOVE the reference mark on the flange.
- Tighten the timing belt tensioner locking nut 15 ft. lbs. (20 Nm).
- Tighten the idler pulley bolts to 30 ft. lbs. (40 Nm).
Install or connect the following:
Crankshaft balancer. Torque the bolts to 15 ft. lbs. (20 Nm).
The 3.4L (VIN X) engine uses a timing chain and camshaft timing belts.
- Disconnect the negative battery cable.
- Disconnect and remove the power steering pump from the pump mounting bracket.
- Remove the left, right and center timing belt covers.
- Rotate the engine clockwise to align the timing marks, TDC on the No.1 exhaust stroke, on the camshaft sprockets and intermediate shaft.
Loosely clamp the two camshaft sprockets on each side of the engine together using clamping pliers or the equivalent. Secure the belt to the right side cam sprocket with a C-clamp and a wide pad on the belt.
NOTEWhen clamping the sprockets no deflection should be noticed. If any deflection is noticed, loosen the clamping devices. DO NOT mar the camshaft sprockets with the clamping device.
- Remove the tensioner side plate retaining bolts from the tensioner and remove the side plate from the actuator and base.
- Rotate the actuator assembly around the arm pivot and out of the base. Removal of the tensioner from the base allows it to extend to its maximum travel.
- Set the actuator aside on a table in a vertical position to allow the oil to drain into the boot end. The tensioner should be allowed to sit for 5 minutes prior to refilling with oil.
Reset the timing belt actuator as follows:
- Straighten out a paper clip or a piece of stiff wire 0.032 in. (0.75mm) diameter to a minimum straight length of 1.85 in. (47mm). Form a double loop in the remaining end.
- Remove the rubber end plug from the rear of the tensioner assembly. This will aid in allowing the oil in the tensioner to escape.
- Hold the tensioner in your hand with the rubber boot end of the tensioner pointing down.
- DO NOT remove the vent plug. Push the paper clip through the center hole in the vent plug and into the pilot hole.
- Insert a small screwdriver into the screw slot inside the end of the tensioner.
- Retract the tensioner by rotating the tensioner plunger in a clockwise direction while pushing the rod tip against a table top.
- Align the screw slot to align with the vent hole, and push the straight section of the wire into the screw slot to retain the plunger in the retracted position.
- If tensioner oil has been lost, fill the tensioner with SAE 5W30 Mobil 1®. Fill the tensioner to the bottom of the plug. The tensioner MUST be fully retracted before being filled with oil.
- If the belt is being reused, mark the direction of rotation on the belt.
- Remove the timing belt tensioner pulley mounting bolt and pulley.
- Remove the timing belt after first removing the C-clamp retaining the belt to the right side camshaft sprocket.
- Remove the Torx® head bolts securing the idler pulleys, if the idlers need to be replaced.
Remove the intermediate shaft sprocket using the following procedure:
- Use a suitable tool to hold the engine from turning.
- Remove the intermediate shaft sprocket mounting bolt and washer.
- Using J-38616 sprocket puller, remove the sprocket from the intermediate shaft.
If the camshaft sprockets need to be removed, proceed as follows:
- Remove the camshaft carrier cover(s).
- Remove the camshaft sprocket clamping pliers.
- Rotate the camshaft being serviced so the flats on the camshaft are face up.
- Install a camshaft hold-down tool J-38613, and tighten to 22 ft. lbs. (30 Nm).
- Remove the camshaft sprocket mounting bolt and washer while holding the camshaft from turning with J-38613 and J-38614.
- Using J-38616 sprocket puller, remove the sprocket from the camshaft.
- Repeat for each camshaft sprocket as necessary.
- Drain the cooling system.
- Disconnect the lower radiator hose from water pump inlet pipe.
- If equipped with a manual transaxle, disconnect the front AIR hose from the AIR pipe.
- Disconnect the heater hose at the front cover.
- Remove the heater pipe bracket mounting bolts at the frame.
- Remove the right front tire and wheel assembly and the right inner fender splash-shield.
- Remove the crankshaft pulley mounting bolts and remove the pulley from the damper.
Remove the crankshaft damper as follows:
- While holding the crankshaft from turning using a suitable tool, remove the damper mounting bolt and washer.
- Install tool J-24420-B and remove the damper from the crankshaft.
- Place an oil catch pan under the oil filter and remove the oil filter.
- Remove the A/C compressor mounting bracket bolts.
- Remove the lower front cover bolts.
- On automatic transaxle vehicles, remove the halfshaft following the recommended procedure.
- Remove the rear alternator bracket.
- Disconnect and remove the starter following the recommended procedure.
- Remove the intermediate shaft drive belt sprocket retaining bolt and remove the intermediate shaft drive belt sprocket using puller J38616.
- Remove the upper alternator mounting bolts.
- Remove the forward light relay center screws and position the relay center aside.
- Disconnect the oil cooler hose from the front cover.
- Remove the water pump pulley.
- Remove the upper front cover bolts and remove the front cover.
- Mark the intermediate shaft sprocket, chain link, crankshaft sprocket and cylinder block for assembly reference. The marks should be made with paint so they won't be lost when the components are removed.
Retract the timing chain tensioner shoe as follows:
- Insert tool J-33875 on both sides of the tensioner.
- Pull on the through-pin in the tensioner arm to retract the spring located in the tensioner arm.
While compressing the spring, use a suitable tool, a cotter pin or nail, and insert the pin in the hole in the tensioner assembly to hold the tensioner compressed. The tool used must be strong enough to hold the tensioner compressed.
NOTEThe timing chain, crankshaft sprocket and intermediate shaft sprocket will be removed at the same time. If, when removing the assembly, the intermediate shaft sprocket does not easily come off the intermediate shaft, rotate the crankshaft back and forth to loosen the intermediate shaft sprocket.
- Install a suitable puller, J-38611 and J-8433.
- Tighten the bolt on the puller and slowly pull the crankshaft sprocket off the crankshaft. Be sure the intermediate shaft sprocket is moving along with the crankshaft sprocket.
- Remove the timing chain and sprockets.
Remove the tensioner mounting bolts and remove the tensioner assembly.
- Install the tensioner assembly and tensioner assembly mounting bolts finger-tight first. Tighten the bolt in the slotted hole first to 18 ft. lbs. (25 Nm), then tighten the remainder of the bolts to 18 ft. lbs. (25 Nm).
- Check to ensure that the crankshaft key is fully seated in the crankshaft cutout and the tensioner assembly is fully retracted.
- Assemble the timing chain, intermediate shaft sprocket and crankshaft sprocket on a work bench. The timing marks made should be in alignment. The large chamfer and counterbore of the crankshaft sprocket are installed facing toward the engine and the intermediate shaft spline sockets are installed facing away from the engine.
- Install the sprocket and chain assembly onto the engine. As the sprockets are installed, parallel alignment must be maintained.
- The crankshaft sprocket will have to be pressed on the final 0.31 in. (8mm). This can be done using J-38612 or an equivalent puller.
- Ensure timing was maintained.
- Remove the retaining pin from tensioner. Clean all gasket surfaces completely.
- Apply GM Sealer 1052080 to the lower edges of the sealing surface of the front cover. Install a new gasket on the front cover.
- Install the front cover on the engine. Apply thread sealant to the large bolts and tighten the bolts enough to pull the front cover against the engine block.
- Install the water pump pulley.
- Connect the oil cooler hose to the front cover.
- Position the forward light relay center and install the mounting screws.
- Install the upper alternator mounting bolt and tighten it to 22 ft. lbs. (30 Nm).
- Install the intermediate shaft drive belt sprocket. The sprocket must lock into the intermediate shaft timing chain sprocket. Install the mounting bolt and washer. While holding the engine from turning, tighten the bolt to 95 ft. lbs. (130 Nm).
- Connect and install the starter. Tighten the starter mounting bolts to 32 ft. lbs. (43 Nm).
- Install the halfshaft following the recommended procedure.
- Install the rear alternator bracket. Tighten the mounting bolt to 22 ft. lbs. (30 Nm) and the mounting stud to 41 ft. lbs. (55 Nm) and the lower bolt to 61 ft. lbs. (83 Nm).
- Install the lower front cover bolts and tighten the small bolts to 18 ft. lbs. (25 Nm).
- Install the A/C compressor mounting bolts and tighten the mounting bolts to 37 ft. lbs. (50 Nm).
- Install a new oil filter.
Install the crankshaft damper as follows:
- Coat the seal contact area on the damper with clean engine oil.
- Align the notch inside the damper with the crankshaft key and slide the damper on until the key is started into the notch.
- Using J-29113 puller, press the damper into position on the crankshaft.
- Install the crankshaft pulley and pulley mounting bolts. Tighten the pulley mounting bolts to 37 ft. lbs. (50 Nm).
- Install the crankshaft damper mounting bolt and washer, and tighten to 78 ft. lbs. (105 Nm).
- Install the right side inner fender splash-shield.
- Install the tire and wheel assembly.
- Tighten the upper front cover small bolts to 18 ft. lbs. (25 Nm) and the large bolts to 35 ft. lbs. (47 Nm).
- Connect the heater hose to the front cover.
- Install the heater pipe bracket mounting bolts.
- If equipped with a manual transaxle, connect the front AIR hose to the AIR pipe.
- Connect the lower radiator hose to the water pump.
- Install the right side cooling fan. Install the upper radiator support.
- Position the torque strut mounting bracket and install the mounting bolts and tighten to 52 ft. lbs. (70 Nm).
- Install the front engine lift hook and tighten the mounting bolt to 52 ft. lbs. (70 Nm).
To install the camshaft sprockets, proceed as follows:
- Wipe the camshaft noses with clean engine oil.
- Install the camshaft sprocket onto the nose of the camshaft.
- Install the lockring and shim ring.
- Install, but DO NOT tighten, the camshaft sprocket mounting bolts at this time.
Install the intermediate shaft sprocket as follows:
- Lubricate the seal contact area on the intermediate shaft sprocket with clean engine oil.
- Slide the sprocket through the intermediate shaft sprocket seal and engage the locking tangs into the sockets of the chain sprocket.
- Lightly lubricate the shaft seal and place it in position on the end of the intermediate shaft.
- Install the intermediate shaft sprocket mounting bolt and washer. Tighten the bolt to 96 ft. lbs. (130 Nm) while holding the crankshaft from turning.
- Install the timing belt idler pulleys and tighten the Torx® bolts to 37 ft. lbs. (50 Nm).
- Install the actuator assembly and side plate. Tighten the actuator mounting bracket bolts to 37 ft. lbs. (50 Nm).
- Install the belt, taking note of direction of rotation if the old belt was used.
- Install the tensioner pulley to the mounting base. Tighten the bolt to 37 ft. lbs. (50 Nm).
- Rotate the tensioner pulley counterclockwise into the belt using the cast square lug on the body and engage the ball end of the actuator into the socket on the pulley arm.
- Remove the tensioner lockpin allowing the tensioner shaft to extend and the pulley to move into the belt.
- Rotate the tensioner pulley counterclockwise, applying 14 ft. lbs. (18 Nm) of torque.
Rotate the engine clockwise three times to seat the belt. Align the crankshaft reference marks during the final rotation to TDC. Do not allow the crankshaft to spring back or reverse its direction of rotation.
NOTEThe timing flats on the camshafts should be 180 degrees apart from the left side to the right side. Both camshafts on the same side should be the same.
To perform the camshaft timing procedure, proceed as follows:
- Rotate the camshaft flats up on the right side camshafts and install a camshaft hold-down tool J-38613, and tighten to 22 ft. lbs. (30 Nm).
- Seat the lockring on the right exhaust and intake camshaft sprockets by threading in the mounting bolt and washer.
Hold the sprocket from turning using tool J-38614.
NOTERunning torque of the bolts before seating should be 55 ft. lbs. (75 Nm).
- If less torque is required, replace the shim ring and lockring.
- If more torque is required, replace the shim ring and lockring and inspect the bolts for burrs.
- Seating of the lockring is accomplished when the edge is flush with the sprocket hub.
- With the lockring seated tighten the bolt to final torque of 81 ft. lbs. (110 Nm).
- Remove J-38613.
- Rotate the engine clockwise one full revolution or any number of odd revolutions. DO NOT rotate the engine backward.
- Be sure the timing mark on the damper aligns with the mark on the front cover.
- Repeat Substeps a through i for the left side.
- Install the camshaft carrier covers.
- Install timing the belt left, right and center covers and retaining bolts.
- Connect the negative battery cable.
- Start the engine and verify proper operation and engine performance.