Note: To perform this procedure, you must have the original camshaft locking tool GM#J-44221 or its equivalent.
Removal
1. Set the engine to a position where the first piston is at TDC (see chapter 2B). Remove the valve cover (see subsection 4) and front engine cover (see subsection 6).
2. Move the chain tensioner and fix it by inserting a drill into the hole.
3. Remove the upper chain guide (see illustration).
7.3. Unscrew the two marked bolts and remove the upper chain guide
4. Remove the exhaust camshaft drive device (see illustration). When the bolt tightening force is weakened, it is necessary to fix the camshaft by grasping it with an open-end wrench by the hexagonal section (see illustration).
7.4a. The exhaust camshaft drive device is secured with a designated hexagon socket bolt in the head
7.4b. When the sprocket bolt tightening force is weakened, it is necessary to fix the camshaft by grasping it with an open-end wrench at the designated hexagonal section
5. Remove the intake camshaft sprocket (see illustration), then disconnect from the crankshaft sprocket and remove the chain. When the sprocket bolt tightening force is weakened, it is necessary to fix the camshaft by grasping it with an open-end wrench by the hexagonal section, as during the operation described in the previous paragraph.
7.5. Intake camshaft sprocket bolt
6. Remove the two service hole plugs located on the front of the cylinder head (see illustration).
7.6. Using a hex wrench, remove the marked service hole plugs located on the front of the cylinder bolt head
7. Unscrew the bolt of the drive chain tensioner shoe (right), as well as the chain guide bolt (left), then remove the shoe and guide. Remove the tensioner (if it is supposed to be replaced).
8. Remove the crankshaft sprocket.
Installation
Note: to match the original position of the chain, every seventh link is darker in color.
9. If necessary, install the tensioner and tighten it to the required torque.
10. Install the shoe and guide and tighten their bolts to the required torques.
11. Install two service hole plugs and tighten them to the required torque.
12. Make sure the first piston is still at TDC, then install the camshaft locking tool. The cams located at the front of the camshafts should be facing up, and the grooves located on the rear camshaft shanks should also be facing up (see illustration).
7.12. When the first piston is at TDC (on the compression stroke) The grooves located on the rear shanks must face upward and be parallel to the upper plane of the cylinder head (The grooves are used to connect the blocking device)
13. Install the crankshaft sprocket, then place the chain on the intake camshaft sprocket so that the dark chain link aligns with the mark on the sprocket.
14. Pass the chain through the cylinder head and place it on the crankshaft sprocket, aligning the mark on the sprocket with the dark link.
15. Install the sprocket on the intake camshaft.
Note: To align the sprocket with the camshaft pin, you may have to remove the locking tool and rotate the shaft slightly.
Install the locking device.
16. Raise the drive chain and guide the exhaust camshaft drive unit to its original location, making sure that the mark on the unit sprocket is aligned with the dark chain link.
17. Install the drive unit onto the intake camshaft without fully tightening the bolt.
Note: To align the sprocket with the camshaft pin, you may have to remove the locking tool and rotate the shaft slightly.
18. Turn the exhaust camshaft drive clockwise (when viewed by an observer positioned in front of the device) before stop _
Caution: Drive unit should be installed in full advance position (turned all the way clockwise), otherwise engine damage may occur.
Tighten the bolt to the required torque.
19. Tighten the intake camshaft sprocket bolt to the required torque.
20. Remove the drill from the tensioner, then remove the camshaft locking device.
21. Using the marks, make sure that the timing of the gas distribution mechanism is aligned (see illustrations).
7.21a. When the chain is installed correctly (when the first piston is at TDC on the compression stroke) The mark on the intake camshaft sprocket should align with the dark link...
7.21b....as well as a mark on the exhaust camshaft drive unit (the mark on the sprocket should also align with the dark link)
22. The remainder of the assembly is performed in the reverse order of removal.