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
3.0L (Vg30de) Engine
- Remove all necessary components for access to the front timing covers, then remove the covers.
- Set the No. 1 cylinder on Top Dead Center (TDC) of the compression stroke.
- The automatic belt tensioner is oil damped and spring operated. Install a 6mm bolt to hold the tensioner back against the spring and release tension on the belt.
Remove the auto-tensioner and timing belt.
WARNINGDo not rotate the crankshaft or camshaft separately because the pistons will strike the valves causing engine damage.
- Confirm that the No. 1 cylinder is at TDC of the compression stroke.
- Align the marks on the camshaft and crankshaft sprockets with the marks on the rear belt cover and oil pump housing.
- With the arrows on the timing belt pointing towards the front, align the white lines on the timing belt with the marks on the sprockets and install the belt.
To prepare the auto-tensioner for installation, perform the following:
- Remove the bolt holding the tensioner in position.
- Use a vise to adjust the gap between the tensioner arm and pusher body to 0.160 in. (4mm).
- Install the bolt again to hold the arm in this position. Do not try to use the bolt to adjust the gap or the threads will be damaged.
- Install the auto-tensioner, push it towards the belt to just take up the slack, then tighten the bolts finger-tight.
Before adjusting the timing belt tension, the slack must be properly distributed:
- Turn the crankshaft 10 degrees clockwise and tighten the tensioner bolts and nut to 12-15 ft. lbs. (16-21 Nm). Do not push the auto-tensioner hard or the belt will be adjusted too tight.
- Turn the crankshaft 120 degrees ( 1 / 3 turn) counterclockwise.
- Loosen the tensioner bolts and nut 1 / 2 turn and move the tensioner body away from the timing belt as far as it will move.
- Turn the crankshaft clockwise to TDC again.
- Push the tensioner against the belt with a force of 13 lbs. (59 N) using a spring scale or similar tool and tighten the bolts again to 12-15 ft. lbs. (16-21 Nm). The pressure specification is important and a special spring scale tool, J-38387, is available to measure the tensioner force.
To check the timing belt tension:
- Turn the crankshaft 120 degrees ( 1 / 3 turn) clockwise, then turn counterclockwise and return the engine to TDC.
- Prepare a steel plate that is approximately 3 / 8 in. (10mm) wide and longer than the width of the belt.
- Set the plate on the timing belt between two camshaft sprockets and push against the plate with a force of 11 lbs. (49 N). Note the belt deflection.
- Repeat the procedure between the other camshaft sprockets and between the exhaust sprockets and idler/tensioner pulleys. There will be a total of four measurements.
- Add the deflection measurements and divide by four. The average deflection must be 0.240-0.280 in. (6-7mm). If belt tension is not correct, start the entire adjustment procedure again.
- Confirm the auto-tensioner mounting nuts are tightened to 12-15 ft. lbs. (16-21 Nm) and remove the auto-tensioner stopper bolt.
- After 5 minutes, measure the clearance between the tensioner arm and the pusher. It should be 0.138-0.205 in. (3.5-5.2mm).
- Be sure all the sprocket timing marks are correctly aligned. Install the timing belt covers and tighten the bolts to 24-38 inch lbs. (3-5 Nm).
- Install all applicable components.