Tools Required

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. Refer to

   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.

   in General Information.
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 line up with the holes in the timing chain housing.



4. The crankshaft sprocket keyway should point upwards and line up 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 sub-section General Information.
7. Ensure that all of the slack in the timing chain is above the tensioner assembly.
8. Remove the timing chain tensioner.
9. The timing chain must be disengaged from any wear grooves in the tensioner shoe in order to remove the shoe. Slide a screwdriver blade under the timing chain while pulling the shoe outward.

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

10. If difficulty is encountered in removing the timing chain tensioner shoe, use the following procedure in order to remove the intake camshaft sprocket:

10.1.

Lower the vehicle.

10.2.

Hold the intake camshaft sprocket with the J 39579 and remove the sprocket bolt and washer.

10.3.

Remove the washer from the bolt and rethread the bolt back into the camshaft by hand (the bolt provides a surface to push against).

10.4.

Remove the intake camshaft sprocket. Use a three-jaw puller in the three relief holes in the sprocket.




11. Remove the tensioner assembly retaining bolts and tensioner.

Important: The timing chain and the crankshaft sprocket must be marked 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.

12. Mark the crankshaft sprocket and the timing chain outer surface.
13. Remove the timing chain.
14. Clean the old sealant off of the bolt with a wire brush.
15. Clean the threaded hole in the camshaft with a round nylon bristle brush.
16. Inspect the parts for wear. Replace the parts as necessary.

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

Notice: Failure to follow this procedure could result in severe engine damage.




1. Install the intake camshaft sprocket onto the camshaft with the marked surface showing.
2. Install the intake camshaft sprocket retaining bolt and washer.

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

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.

3. Use Adhesive/Sealant Compound GM P/N 12345493 or equivalent on the camshaft sprocket bolt.
4. Install the J 36800 through the holes in the camshaft sprockets into the holes in the timing chain housing in order to position the camshaft for correct timing.
5. If the camshafts are out of position and must be rotated more than 1/8 turn in order to install the alignment dowel pins, use the following procedure:

5.1.	The crankshaft must be rotated 90 degrees clockwise off of the TDC in order to give the valves adequate clearance to open.

5.2.	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.

6. Install the timing chain over the exhaust camshaft sprocket, around the idler sprocket and around the crankshaft sprocket.



7. Set the camshaft sprockets at the timed position. Use the following procedure in order to install the timing chain:

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

7.2.	Use the J 39579 in order to rotate the intake camshaft sprocket counterclockwise enough to slide the timing chain over the intake camshaft sprocket.

7.3.	Release the J 39579 . The length of the chain between the two camshaft sprockets will tighten.

7.4.	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.

8. Leave the alignment dowel pins installed.
9. Raise and support the vehicle. Refer to sub-section General Information.
10. With the slack removed from the chain between the intake camshaft sprocket and the crankshaft sprocket, the timing marks on the crankshaft and the cylinder block should be aligned. If the marks are not aligned, move the chain one tooth forward or rearward, remove the slack and the recheck marks.




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

11. Reset the timing chain tensioner assembly:

11.1.

Insert the tensioner plunger assembly into the tensioner housing.

11.2.

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

11.3.

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

11.4.

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




12. 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.



13. Loosely install the tensioner assembly and bolts to the timing chain housing.
14. Install the timing chain tensioner shoe on the stud.
15. Apply hand pressure to the timing chain tensioner shoe until the locking tab seats in the groove in the stud.
16. 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.

17. Release the timing chain tensioner plunger.

17.1.

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.

17.2.

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

17.3.

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

18. Remove J 36800 from the camshaft sprockets.
19. 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.



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

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