Tools Required

Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

Notice: The timing chain on the LD9 (VIN T) Twin Cam Engine is not to be replaced with the timing chain from any other model year. The timing sprockets are different on the Twin Cam engine and the shape of the links matches the sprockets. Engine damage may result if the wrong timing chain is used. The timing chain and the crankshaft sprocket must be marked so that they are reinstalled in the same side facing out at the time of reassembly.

1. Disconnect the negative battery cable.
2. Remove the engine front cover. Refer to Engine Front Cover Replacement .
3. Rotate the crankshaft clockwise (as viewed from the front of the engine, normal rotation) until the camshaft sprocket timing dowel pin holes align with the holes in the timing chain housing.



4. Set the crankshaft sprocket keyway pointing upwards. Align with the centerline of the cylinder bores. This is the timed position.
5. Remove the timing chain guides.
6. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
7. Ensure that all of the slack in the timing chain is above the tensioner assembly.
8. Remove the timing chain tensioner bolts and the tensioner.



9. Remove the tensioner shoe. Use a small locking ring plier in order to engage the hole in the locking tab and remove the shoe from the stud.




Notice: Do not attempt to pry the sprocket off the camshaft or damage to the sprocket or chain housing could occur.

Important: Mark the timing chain and the crankshaft sprocket prior to removal. If the chain or the crankshaft sprocket is installed with the wear pattern in the opposite direction, noise and increased wear may occur.

10. Mark the crankshaft sprocket and the timing chain outer surface.
11. Remove the timing chain.
12. Lower the vehicle.



13. Holding the intake camshaft sprocket with J 39579 , remove the sprocket bolt and washer.
14. Remove the washer from the bolt and rethread the bolt back into the camshaft.
15. Using a 3-jaw puller and the relief holes in the sprocket, remove the intake camshaft sprocket.
16. Repeat this procedure for the exhaust camshaft sprocket.
17. Clean the old sealant from the bolt with a wire brush.
18. Clean the threaded hole in the camshaft with a round nylon bristle brush.
19. Inspect the parts for wear. Replace the parts as necessary.

Some scoring of the timing chain shoe and the guides is normal.

20. Replace the timing chain shoe or guides if the scoring exceeds 1.12 mm (45 in).

1. Use Adhesive/Sealant Compound GM P/N 12345493 or equivalent on the camshaft sprocket bolt.

Install the intake and exhaust camshaft sprockets onto the camshafts with the marked surface showing.

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

2. Install the retaining bolts and washers to the intake and exhaust camshaft sprockets.

Tighten
Tighten the bolts to 70 N·m (52 lb ft) while holding the sprockets with the J 39579 .

3. Install the J 36800 through the holes in the camshaft sprockets into the holes in the timing chain housing. This will position the camshaft for correct timing.
4. If the camshafts are out of position (you must rotate the camshaft more than 1/8 turn in order to install the alignment dowel pins), use the following procedure:

4.1.	Rotate the crankshaft 90 degrees clockwise off of the TDC in order to give the valves adequate clearance to open.

4.2.	Once the camshafts are in position and the dowels installed, rotate the crankshaft counter clockwise back to the top dead center.





Notice: Do not rotate the crankshaft clockwise to TDC. Valve or piston damage could occur.

Important: The side of the timing chain that was marked during removal must be showing when the chain is installed.

5. Install the timing chain over the exhaust camshaft sprocket, around the coolant pump, and around the crankshaft sprocket.

5.1.	Remove the alignment dowel pin from the intake camshaft.

5.2.	Using the J 39579 , rotate the intake camshaft sprocket counterclockwise enough in order to slide the timing chain over the intake camshaft sprocket.

5.3.	Release the J 39579 . The length of the chain between the 2 camshaft sprockets will tighten.

5.4.	If properly timed the intake camshaft alignment dowel pin should slide in easily. If the dowel pin does not fully index, the camshafts are not timed correctly and the procedure must be repeated.

6. Leave the alignment dowel pins installed.
7. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
8. The timing marks on the crankshaft and on the cylinder block should be aligned when the slack is removed from the chain linking the intake camshaft sprocket and the crankshaft sprocket. If the marks are not aligned, move the chain one tooth forward or rearward, remove the slack and re-examine the marks.




Important: Use the following steps in order to reset the timing chain tensioner assembly to the zero position.

9. Reset the timing chain tensioner assembly.

9.1.	Insert the tensioner plunger assembly into the tensioner housing.

9.2.	With the tensioner plunger fully extended, turn the complete assembly upside down on a bench or other flat surface.

9.3.	With the plunger face against the workbench, press firmly on the bottom of the tensioner housing.

9.4.	Compress the plunger until the plunger is seated flush in the tensioner.




10. Check the plunger to make sure the plunger is out of the cylinder at the correct dimension. The correct dimension for the plunger to extend out of the cylinder is 1.7 mm (0.07 in) maximum.



11. Loosely install the tensioner assembly and bolts to the timing chain housing.
12. Install the timing chain tensioner shoe on the stud.
13. Apply hand pressure to the timing chain tensioner shoe until the locking tab seats in the groove in the stud.
14. Tighten the timing chain tensioner bolts. Do Not overtighten.

Tighten
Tighten the bolts to 10 N·m (89 lb in).





Important: If the timing chain tensioner is not released from the installation position, engine damage will occur when the engine is started.

15. Release the timing chain tensioner plunger.

15.1.

Using a flat blade screwdriver, cotter pin remover, or similar tool, press firmly against the face of the timing chain tensioner plunger.

Important: If the timing chain tensioner cannot be depressed, the plunger is not properly reset and the procedure for resetting the timing chain tensioner should be repeated.

15.2.

Depress the timing chain tensioner plunger until the plunger is bottomed out in the bore of the timing chain tensioner.

15.3.

Release the tensioner plunger. the plunger should press firmly against the back of the timing chain tensioner shoe.

16. Remove J 36800 from the camshaft sprockets.
17. Rotate the crankshaft clockwise 2 full rotations. Align the crankshaft keyway with the mark on the cylinder block, and reinstall the alignment dowel pins. The pins should slide in easily if the engine is timed correctly.



18. Install the timing chain guides.
19. Install the engine front cover. Refer to Engine Front Cover Replacement .
20. Connect the negative battery cable.

Tighten
Tighten the bolt to 16 N·m (12 lb ft).