Timing Chain: Service and Repair

Lower Engine:

Timing Chain "Timed Position":

Tensioner Spring And Retainer:

Timing Chain Hydraulic Tensioner:

SPECIAL TOOLS REQUIRED (or equivalents)
^ J-36013, Camshaft sprocket wrench.
^ J-36008, Camshaft timing alignment pins.
^ J-36589, Timing chain tensioner spacer.

CAUTION: Before removing the timing chain, read the entire procedure for removal and installation. Failure to follow these procedures could result in severe engine damage.

REMOVE OR DISCONNECT
1. Engine front cover, refer to Timing Cover / Service and Repair.
2. Rotate crankshaft clockwise (as viewed from front of engine / normal rotation) until the camshaft sprockets timing dowel pin holes line up with the holes in the timing chain housing.
a. The mark on the crankshaft sprocket should line up with the mark on the cylinder block.
b. The crankshaft sprocket keyway should point upwards and line up with the centerline of the cylinder bores. This is the "Timed" position.

3. Timing chain guides.
4. Raise the vehicle.
5. On early production vehicles, gently pry off timing chain tensioner spring retainer and remove spring (these parts may be discarded).
6. Make sure all the slack in the timing chain is above the tensioner assembly, then remove the chain tensioner shoe.

NOTE: 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. If difficulty is encountered in removing the chain tensioner shoe, proceed as follows:
a. Lower the vehicle.
b. Hold the intake camshaft sprocket with J-36013 or equivalent and remove the sprocket bolt and washer.
c. Remove the washer from the bolt and rethread the bolt back into the camshaft by hand (the bolt provides a surface to push against).
d. Remove intake cam sprocket using a three-jaw puller in the three relief holes in the sprocket.

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

7. Tensioner assembly retaining bolts and tensioner.

WARNING: Tensioner piston is spring loaded and could come out causing personal injury.

8. Chain housing to block stud (48).
9. Timing chain.
10. Inspect parts for wear and replace as required. Some scoring of the timing chain shoe and guides is normal.

INSTALL OR CONNECT
1. Clean the threaded hole in the camshaft and the old sealant off of the bolt.
2. Use GM P/N 12345493 or equivalent on camshaft sprocket bolt. Install intake sprocket and using J-36013, torque to 70 Nm (52 lbs ft) (if removed).
3. J-36008 or equivalent through holes in camshaft sprockets into holes in timing chain housing (this positions the camshafts for correct timing). If the camshafts are out of position and must be rotated more than 1/8 turn in order to install the alignment dowel pins:
a. The crankshaft MUST be rotated 90° clockwise off of TDC in order to give the valves adequate clearance to open.
b. Once the camshafts are in position and the dowels installed, rotate the crankshaft COUNTER CLOCKWISE back to top dead center.

CAUTION: Do not rotate the crankshaft clockwise to TDC, valve or piston damage could occur.

4. Timing chain over exhaust camshaft sprocket around idler sprocket and around crankshaft sprocket.
5. Remove the alignment dowel pin J-36008 from the intake camshaft. Using J-36013 rotate the intake camshaft sprocket counter clockwise enough to slide the timing chain over the intake camshaft sprocket, then release J-36013. The length of chain between the two camshaft sprockets will tighten. If properly timed the intake cam 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 and raise the vehicle.
7. With slack removed from chain between intake cam sprocket and 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 slack and recheck marks.

8. Chain housing to block stud (48) and torque to 26 Nm (19 lbs ft).

NOTE: Two styles of tensioner are used. One with a spring post (early production), and one without a spring post (late production). Both styles are identical in operation and are interchangeable. The early production spring and retainer are not needed, DO NOT REINSTALL.

9. Reload timing chain tensioner assembly to its "zero" position as follows:
a. Assemble restraint cylinder, spring and nylon plug into plunger. Index slot in restraint cylinder with peg in plunger. While rotating the restraint cylinder clockwise, push the restraint cylinder into the cylinder until it bottoms. Keep rotating the restraint cylinder clockwise but allow the spring to push it out of the plunger. The pin in the plunger will lock the restraint in the loaded position.
b. Tool J-36589 onto plunger assembly.
c. Plunger assembly into tensioner body with the long end toward the crankshaft when installed.

10. Tensioner assembly (54) to chain housing. Recheck plunger assembly installation, it is correctly installed when the long end is toward the crankshaft.
11. Timing chain tensioner bolts (70) and tighten to 13 Nm (115 lbs in).
12. Tensioner shoe (51) and shoe retainer.
13. Remove J-36589 and squeeze plunger assembly into tensioner body to unload the the plunger assembly.
14. Lower the vehicle enough to reach and remove the alignment dowel pins.
15. Rotate the crankshaft clockwise (normal rotation) two full rotations. Align crankshaft timing mark with mark on cylinder block and reinstall alignment dowel pins. Alignment dowel pins will slide in easily if engine is timed correctly.

CAUTION: If the engine is not correctly timed, severe engine damage could occur.

16. Three timing chain guides.
17. Crankshaft oil slinger.
18. Engine front cover, refer to Timing Cover / Service and Repair.
19. Start the engine and inspect for oil leaks.