Assuming that you don't have the supercharged engine:

Document ID# 216078
1998 Pontiac Bonneville
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Drive Belt Replacement VIN K
Removal Procedure
The accessory drive belt controls all engine-mounted accessories. All driven
accessories rigidly mount to the engine. A spring-loaded belt tensioner
maintains the drive belt tension. A belt squeak, occurring when starting or
stopping the engine, it has not effect on belt durability. The drive belt
tensioner can control the belt tension over a broad range of belt length.
However, there are limits to the tensioner's compensation ability. When
using the tensioner outside of its operating range, poor tension control
and/or damage to the tensioner may occur.

Remove the following components. Refer to Engine Mount Replacement (further
down this page).

The engine mounting bracket lower nut.
The engine mounting bracket lower stud.
The engine mounting bracket lower spacer.
Remove the belt.

Installation Procedure
Install the belt. Refer to Engine Mount Replacement in order to install the
following components:
The engine mounting bracket lower nut.
The engine mounting bracket lower stud.
The engine mounting bracket lower spacer.

Document ID# 216113
1998 Pontiac Bonneville
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Engine Mount Replacement
Removal Procedure
Tools Required
J 28467-360 Engine Support Fixture

Caution
Before servicing any electrical component, the ignition key must be in the
OFF or LOCK position and all electrical loads must be OFF, unless instructed
otherwise in these procedures. If a tool or equipment could easily come in
contact with a live exposed electrical terminal, also disconnect the
negative battery cable. Failure to follow these precautions may cause
personal injury and/or damage to the vehicle or its components.

Disconnect the negative battery cable.
Install the J 28467-360 .
For Engine Code 1, remove the ignition module. Set the module aside.
Remove the accessory drive belt. Refer to Drive Belt Replacement .
For Engine Code 1, remove the supercharger drive belt tensioner.
Remove the power steering pump. Set the power steering pump aside. Refer to
Power Steering Pump Replacement in Power Steering System.
Remove the torque axis engine mount.
Remove the nuts from the engine mount bracket.
Remove the studs from the engine mount bracket.
Remove the torque axis engine mount bracket.

Installation Procedure

Install the torque axis engine mount bracket.
Install the studs to the engine mount bracket.

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.

Install the nuts to the engine mount bracket. Tighten
Tighten the upper nut to 30 N·m (22 lb ft).
Tighten the lower nut to 70 N·m (52 lb ft).
Install the torque axis engine mount.
Install the power steering pump. Refer to Power Steering Pump Replacement in
Power Steering System.
For Engine Code 1, install the supercharger belt tensioner. Refer to Drive
Belt Tensioner Replacement .
For Engine Code 1, install the ignition module.
Install the accessory drive belt. Refer to Drive Belt Replacement .
Remove the J 28467-360 .
Connect the negative battery cable.