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MZ145 Excavator Overview
The MZ145 is a mid-size hydraulic excavator designed for general construction, utility trenching, and demolition work. Manufactured by Mitsubishi Heavy Industries in collaboration with other OEMs, the MZ145 features a robust swing system, open-center hydraulics, and a mechanical control layout. With an operating weight around 14 metric tons and a digging depth exceeding 18 feet, the machine balances reach, stability, and transportability. Though not as widely distributed as Hitachi or Komatsu models, the MZ145 has earned a reputation for reliability in fleet operations across Southeast Asia and parts of North America.
Terminology Notes
Operators have reported noticeable swing play in the MZ145, with the boom moving up to 12 inches side-to-side when stationary. This over-swing during operation can reduce precision and increase wear on the swing gear. Initial inspection reveals that the swing motor is mounted on a plate secured by bolts and tack welds, suggesting potential for adjustment. However, the absence of a visible swing brake or resistance mechanism raises questions about the root cause.
Possible Causes and Diagnostic Strategy
In New South Wales, a contractor noticed excessive swing play on his MZ145 after 6,000 hours of operation. He removed the swing motor and inspected the pinion teeth, finding uneven wear. Rather than replacing the entire gear set, he shimmed the motor plate and reduced backlash by 40%. The machine regained acceptable precision for trenching work.
In Oregon, a fleet mechanic traced swing drift to a failed pilot-operated check valve in the swing circuit. Replacing the valve restored brake function and eliminated the over-swing. He emphasized that not all swing systems use mechanical brakes—some rely entirely on hydraulic resistance.
Recommendations for Technicians and Owners
Swing play in the MZ145 excavator can stem from gear wear, hydraulic drift, or lack of braking resistance. While some adjustment may be possible via motor repositioning, the most effective solution often lies in restoring hydraulic lock or replacing worn components. With careful inspection and targeted repairs, operators can regain control precision and extend the life of the swing system.
The MZ145 is a mid-size hydraulic excavator designed for general construction, utility trenching, and demolition work. Manufactured by Mitsubishi Heavy Industries in collaboration with other OEMs, the MZ145 features a robust swing system, open-center hydraulics, and a mechanical control layout. With an operating weight around 14 metric tons and a digging depth exceeding 18 feet, the machine balances reach, stability, and transportability. Though not as widely distributed as Hitachi or Komatsu models, the MZ145 has earned a reputation for reliability in fleet operations across Southeast Asia and parts of North America.
Terminology Notes
- Swing Motor: A hydraulic motor that drives the rotation of the upper structure.
- Turntable Ring Gear: A large gear mounted to the swing bearing, engaged by the swing motor pinion.
- Backlash: The amount of free movement between gear teeth before engagement.
- Swing Brake: A hydraulic or mechanical system that resists movement when the swing function is not activated.
Operators have reported noticeable swing play in the MZ145, with the boom moving up to 12 inches side-to-side when stationary. This over-swing during operation can reduce precision and increase wear on the swing gear. Initial inspection reveals that the swing motor is mounted on a plate secured by bolts and tack welds, suggesting potential for adjustment. However, the absence of a visible swing brake or resistance mechanism raises questions about the root cause.
Possible Causes and Diagnostic Strategy
- Gear Backlash from Wear
Over time, the engagement between the swing motor pinion and the turntable ring gear may develop excessive clearance. This is common in machines with high swing cycles or poor lubrication history.
- Lack of Swing Brake or Hydraulic Lock
If the swing motor lacks a brake valve or hydraulic lock, the upper structure may drift or oscillate under residual pressure. Some systems rely on counterbalance valves or pilot-operated check valves to hold position.
- Motor Mounting Plate Shift
If the swing motor plate was originally designed for adjustment, it may be possible to reduce backlash by repositioning the motor closer to the ring gear. However, tack welds and fixed bolt patterns may limit this option.
- Hydraulic Drift or Valve Leakage
Internal leakage in the swing control valve can allow unintended movement, especially when the machine is off or idling. Checking the hydraulic diagram may reveal a brake valve or lockout circuit.
In New South Wales, a contractor noticed excessive swing play on his MZ145 after 6,000 hours of operation. He removed the swing motor and inspected the pinion teeth, finding uneven wear. Rather than replacing the entire gear set, he shimmed the motor plate and reduced backlash by 40%. The machine regained acceptable precision for trenching work.
In Oregon, a fleet mechanic traced swing drift to a failed pilot-operated check valve in the swing circuit. Replacing the valve restored brake function and eliminated the over-swing. He emphasized that not all swing systems use mechanical brakes—some rely entirely on hydraulic resistance.
Recommendations for Technicians and Owners
- Inspect Swing Gear Engagement: Measure backlash and check for uneven wear.
- Review Hydraulic Schematic: Identify any brake valves, lockout circuits, or counterbalance valves.
- Test for Drift with Engine Off: If the boom moves under gravity, hydraulic lock may be compromised.
- Consider Shimming or Repositioning the Motor: Only if the mounting plate allows safe adjustment.
- Use High-Viscosity Gear Lubricant: Reduces wear and dampens movement in older gear sets.
Swing play in the MZ145 excavator can stem from gear wear, hydraulic drift, or lack of braking resistance. While some adjustment may be possible via motor repositioning, the most effective solution often lies in restoring hydraulic lock or replacing worn components. With careful inspection and targeted repairs, operators can regain control precision and extend the life of the swing system.
