The 1997-2005 Buick Century Repair Manual by Haynes Manuals, covers models indicated, equipped with V-6 gasoline engines. U.S. and Canadian models.
Book Excerpt: 1997-2005 Buick Century Repair Manual
3.8L V6 ENGINE
Check each rocker arm for wear, cracks and other damage, especially where the pushrods and valve stems contact the rocker arm.
Check the pivot seat in each rocker arm and the pivot faces. Look for galling, street cracks and unusual wear patterns. If the rocker arms are worn or damaged, replace them with new ones and install new pivots or shafts as well.
Make sure the hole at the pushrod end of each rocker arm is open.
Inspect the pushrods for cracks and excessive wear at the ends. Roll each pushrod across a piece of plate glass to see if it's bent (if it wobbles, it's bent).
Lubricate the lower end of each pushrod with clean engine oil or moly-base grease and install them in their original locations. Make sure each pushrod seats completely in the lifter socket.
Apply moly-base grease to the ends of the valve stems, the upper ends of the pushrods and to the pivot faces to prevent damage to the mating surfaces before engine oil pressure builds up.
Coat the rocker arm pivot bolts with moly-base grease. Install the pushrod guide plates, rocker arms, pivots and pivot retainers. Tighten the bolts to the torque listed in this Chapter's Specifications. As the bolts are tightened, make sure the pushrods seat properly in the rocker arms.
Install the valve covers (see Section 4).
3.1L V6 ENGINE
INTAKE MANIFOLD: REMOVAL AND INSTALLATION
UPPER INTAKE MANIFOLD: (PLENUM)
(Refer to illustration 7.8)
Disconnect the cable from the negative terminal of the battery. Caution: On models equipped with the Theftlock audio system, be sure the lockout feature is turned off before performing any procedure which requires disconnecting the battery (see the front of this manual).
Refer to Chapter 4 and relieve the fuel system pressure, then remove the air intake duct and detach the throttle cable and the cruise control cable form the throttle body.
Label and disconnect the hoses and electrical connectors attached to the plenum and throttle body. Partially drain the cooling system before disconnecting the coolant hoses at the throttle body.
Refer to Chapter 6 and remove the EGR valve-to-plenum bolts. On some models it may also be necessary to remove the alternator (see Chapter 5).
Remove the spark plug wires and the ignition coil and module assembly (see Chapter 5).
Loosen the upper intake manifold bolts in the reverse order of the tightening sequence (see illustration 7.8) and remove the upper plenum with the throttle body attached. Remember which ones are studs.
To install the upper manifold, clean the mounting surfaces of the lower intake manifold and the upper plenum with lacquer thinner and remove all traces of the old gasket material or sealant.
Install the new gasket over the lower intake manifold, then install the upper plenum onto the lower intake manifold and tighten the bolts in the recommended tightening sequence (see illustration) to the torque listed in this Chapter's Specifications. The remainder of the installation is the reverse of removal.