Grove RT620 Boom Cylinder Replacement and Crane Revival

[MikePhua]

The Grove RT620 and Its Place in Crane History
Grove Manufacturing Company, founded in 1947 in Pennsylvania, became a global leader in mobile hydraulic cranes by the 1970s. Known for pioneering rough terrain crane designs, Grove introduced the RT series to meet the demands of off-road lifting in construction, mining, and energy sectors. The RT620, launched in the late 1980s, was part of Grove’s mid-capacity lineup, offering a blend of compact mobility and robust lifting power.
With a rated lifting capacity of 20 tons and a boom length extending up to 75 feet, the RT620 was designed for versatility. It featured a four-section hydraulic boom, a Cummins diesel engine, and full-time four-wheel drive. By the mid-1990s, Grove had sold thousands of RT620 units across North America, the Middle East, and Southeast Asia, particularly to contractors working in oilfields and remote infrastructure projects.
Boom Cylinder Function and Failure Modes
The boom cylinder is a critical component in any hydraulic crane. On the RT620, it controls the elevation of the boom, allowing precise lifting angles and load positioning. A failure in this cylinder can render the crane inoperable or dangerously unstable.
Common failure modes include:

• Internal seal degradation leading to hydraulic bypass
  
• Rod scoring or pitting from debris or corrosion
  
• Bent cylinder rods due to overload or side loading
  
• External leaks from cracked end caps or worn fittings
  

Terminology notes:

• Hydraulic bypass: A condition where fluid leaks past internal seals, reducing pressure and movement.
  
• Rod scoring: Surface damage on the cylinder rod that compromises seal integrity.
  
• Side loading: A force applied perpendicular to the cylinder’s axis, often causing bending or misalignment.
  

In Alberta, a contractor reported that his RT620’s boom would drift downward under load. After inspection, the boom cylinder was found to have a torn piston seal, allowing fluid to bypass internally. Replacing the seal restored full lifting capability.
Sourcing Used Boom Cylinders and Rebuild Options
Finding a used boom cylinder for the RT620 can be challenging due to limited production and aging fleets. However, several strategies can improve success:

• Contact crane salvage yards specializing in Grove equipment
  
• Search for compatible cylinders from RT58 or RT740 models with similar bore and stroke dimensions
  
• Consult hydraulic rebuild shops for custom re-rod and reseal services
  
• Join regional contractor networks for surplus part exchanges
  

Recommended specifications to verify:

• Bore diameter: typically 5 to 6 inches
  
• Stroke length: approximately 60 to 70 inches
  
• Mounting style: clevis or spherical bearing
  
• Rod diameter: 2.5 to 3 inches
  
• Operating pressure: up to 3,000 psi
  

In Texas, a crane rental company refurbished an RT620 boom cylinder by machining a new rod and installing high-temperature Viton seals. The rebuild cost $3,800—less than half the price of a new OEM cylinder—and extended service life by 5 years.
Hydraulic System Considerations During Replacement
Replacing a boom cylinder requires careful attention to hydraulic cleanliness and system integrity. Contaminants introduced during installation can damage pumps, valves, and other actuators.
Best practices:

• Flush hydraulic lines before connecting new cylinder
  
• Use lint-free cloths and caps during disassembly
  
• Replace inline filters after installation
  
• Bleed air from the system by cycling the boom slowly
  
• Monitor fluid temperature and pressure during initial operation
  

Terminology notes:

• Inline filter: A device placed in the hydraulic circuit to trap particles and protect components.
  
• Bleeding air: The process of removing trapped air from hydraulic lines to prevent erratic movement or cavitation.
  

In Indonesia, a port operator replaced a boom cylinder and neglected to flush the lines. Within weeks, the main control valve began sticking due to debris contamination. A full system flush and valve rebuild were required, costing over $6,000.
Structural and Safety Checks After Cylinder Replacement
Once the boom cylinder is installed, structural integrity and safety systems must be verified. The RT620’s boom relies on synchronized movement and load monitoring to prevent tipping or overextension.
Checklist:

• Inspect boom welds and pivot pins for cracks or wear
  
• Test load moment indicator (LMI) for accuracy
  
• Verify boom angle sensor calibration
  
• Grease all pivot points and wear surfaces
  
• Conduct a full load test under supervision
  

In Florida, a contractor performed a boom cylinder swap and skipped the LMI calibration. During a lift, the system failed to warn of overload, resulting in a boom tip fracture. The incident led to a costly repair and a safety audit.
Operator Stories and Field Wisdom
In New Mexico, a utility crew revived an RT620 that had sat idle for six years. The boom cylinder was seized, and the seals had hardened. After sourcing a used cylinder from a retired RT58 and adapting the mounts, the crane returned to service and was used to install transmission poles in rugged terrain.
In South Africa, a mining firm rebuilt their RT620’s boom cylinder using locally sourced chrome rod and imported seals. The machine was then deployed for underground shaft construction, where its compact footprint and lifting precision proved invaluable.
Conclusion
The Grove RT620 remains a respected workhorse in the rough terrain crane category. While boom cylinder failure can sideline operations, strategic sourcing and careful installation can restore functionality and extend the crane’s life. With proper hydraulic hygiene, structural checks, and calibration, even aging units can continue lifting with confidence. The legacy of the RT620 lives on in job sites where reliability and adaptability still matter most.