1990 Mitsubishi Eclipse Balance Shaft Drive Belt Replacement Cost

The term “Drive Belt” is a generic term used to describe a set of belts that are used to drive engine accessories. The most common drive belts are the alternator belt, power steering pump belt, and air conditioning compressor belt. Some engines use balance shafts to balance internal rotational forces from the engine. While most are driven by timing chains or the timing belt, some have dedicated drive belts known as 'balance shaft drive belts'.

While the engine is running, the crankshaft pulley is constantly spinning. This provides an opportunity to drive other mechanisms by means of a belt. Much like the timing belt or timing chain, the balance shaft belt will wrap around the balance shaft and crankshaft, and secure to toothed gears on both shafts. This causes the balance shaft to rotate at the same speed as the crankshaft, and always remain synchronized.

If the balance shaft belt breaks, there may be strange rubbing or grinding noises from the front of the engine. This is because the timing belt is likely chewing through the balance shaft drive belt as it is likely resting on the teeth of the timing belt. If it is not changed immediately, the engine will being running roughly, and vibration will be evident throughout the vehicle. As a worst-case scenario, internal engine damage may occur due to the balance shaft belt dislodging the timing belt or other timing components. The check engine light will illuminate on the dashboard in the event of total failure or breakage of the balance shaft belt and the vehicle may not start or stay running.

It is not recommended to drive a vehicle suspected of timing component damage, and the balance shaft belt and tensioner are responsible for the timing of the balance shaft to the engine. If the vehicle will run, operating the vehicle may result in damage or total failure to the engine.

Each manufacturer specifies the interval for balance shaft drive belt replacement for each model and year of vehicle produced. Strict adherence to the service intervals will help prevent the occurrence of balance shaft drive belt failure.

If a technician suspects the balance shaft drive belt may be broken, removal of the timing or front cover will allow the technician to determine the accuracy of this suspicion. Also, the technician will ensure proper alignment and operation of the pulley system for the balance shaft belt to determine if there is a more serious problem.

At a minimum, replacement involves removal of the timing cover, balance shaft belt tensioner, balance shaft belt, and the balance shaft belt pulley. The balance shaft belt tensioner is typically attached by one bolt, but installation requires the proper amount of tension to be applied to the balance shaft belt and idler pulley retaining bolt. Once all components are replaced, the timing components can be installed onto the engine, and the engine will be tested for proper operation and balance shaft timing before additional components are replaced.

Since this service requires removal of the balance shaft belt and timing cover, it is recommended to replace the timing belt, water pump and possibly front seals at the same time, unless they have been recently serviced. This is much more cost effective than returning for the same service after a partial service interval has elapsed.

It may be necessary for the motor mounts to be removed from the vehicle, as well as engine cooling fans, the radiator, and all engine accessories. This may include components like the alternator, A/C compressor, mounting brackets, coolant or fuel lines, and any other component that interfere with access to the timing cover or front cover.

Since balance shaft belt replacement necessitates the removal of timing components, it is not recommended for the DIY mechanic to attempt this task. A thorough knowledge of internal engine components, engine timing, accessory systems, and several specialty tools are required to properly perform this repair.