Importance of Proper Lubrication
Lubrication is a critical maintenance component in heavy machinery, ensuring smooth operation by reducing friction and wear between moving parts. Quality lubricants safeguard engines, transmissions, gears, bearings, and hydraulic systems, directly influencing machine longevity, reliability, and performance.
Prioritizing High-Quality Lubricants

• Many operators and fleet managers prefer to invest in premium base lubricants like Shell Rotella for diesel engines, Shell greases for high-load pivot points, and Shell hydraulic oils for reliable system performance.
  
• Beyond these core lubricants, some specialized components benefit from targeted, higher-grade products due to their extreme operating conditions.
  

• Gear Oils: Gears experience high pressures and sliding contact, often needing extreme pressure (EP) additives and specific viscosity grades to minimize wear and prevent pitting.
  
• Wheel Bearing Grease: Bearings demand greases with superior adhesion and water resistance to prevent contamination-related failures.
  
• Hydraulic System Fluids: High-performance hydraulic oils with anti-foam and anti-wear additives maintain system efficiency and longevity.
  
• Extreme Temperature Greases: Components exposed to severe heat or cold require specially formulated greases that maintain viscosity and lubrication properties.
  

• Heavy-duty construction equipment often operates in harsh environments with dirt, moisture, and heavy loads, necessitating robust lubricant protection.
  
• Choosing lubricants matching OEM specifications and regional climate conditions ensures optimal performance.
  
• Ensuring lubricant compatibility across different system components prevents chemical reactions or additive degradation.
  

• Establishing and following rigorous lubrication schedules based on OEM recommendations.
  
• Using calibrated equipment to apply the correct lubricant volume and pressure.
  
• Employing contamination control measures such as clean grease fittings, desiccant breathers, and regular oil analysis.
  
• Training maintenance personnel to understand lubrication nuances reduces risks of over- or under-lubrication.
  
• Maintaining detailed lubrication records facilitates tracking and planning preventive maintenance.
  

• Extreme Pressure (EP) Additives: Chemicals in gear oils enhancing load-carrying capabilities.
  
• Viscosity: Measure of fluid thickness affecting flow and film strength.
  
• Calibrated Grease Gun: Tool adjusted to dispense precise lubricant volumes.
  
• Desiccant Breather: Device preventing moisture and particulates entering reservoirs.
  
• Compatibility: Ability of different lubricants to mix without degradation.
  

The 322L Excavator and Its Legacy
The Caterpillar 322L hydraulic excavator was part of Cat’s L-Series lineup introduced in the late 1990s, designed to meet growing demand for mid-sized machines with enhanced hydraulic control and durability. With an operating weight of approximately 49,000 pounds and a 6-cylinder 3116 turbocharged diesel engine producing around 150 horsepower, the 322L was widely adopted in infrastructure, quarrying, and forestry applications.
Caterpillar Inc., founded in 1925, has consistently led the global earthmoving market, with millions of machines sold across continents. The 322L was particularly popular in North America and Europe, with thousands of units delivered between 1997 and 2002. Its robust undercarriage and modular final drive assembly made it a favorite among contractors seeking long-term reliability.
Sprocket Bolt Failures and Their Root Causes
One recurring issue reported by owners involves the sprocket bolts that secure the drive sprocket to the final drive hub. In several cases, threads within the hub were stripped, either due to improper torque application or poor surface preparation during installation.
Common causes include:

• Overtorquing or undertorquing: Using impact wrenches without torque control can stretch or loosen threads.
  
• Paint contamination: Failing to remove factory paint from mating surfaces reduces friction and leads to bolt loosening.
  
• Surface irregularities: Uneven contact between sprocket and hub can cause bolt shear or misalignment.
  
• Reuse of bolts: Some manufacturers recommend replacing bolts after each removal due to thread fatigue.
  

• Final Drive Hub: The component that transmits torque from the hydraulic motor to the sprocket.
  
• Torque Turn Bolts: Fasteners that require a specific torque followed by a measured angular turn to achieve proper preload.
  
• Thread Inserts: Reinforcement sleeves installed into stripped holes to restore thread integrity.
  

• Clean all mating surfaces thoroughly, removing paint and debris.
  
• Inspect bolt holes for concentricity and depth.
  
• Use anti-seize or thread locker based on manufacturer guidance.
  
• Torque bolts in a star pattern to ensure even preload.
  
• Recheck torque after initial operation to confirm stability.
  

• Check bolt torque every 250 hours or after heavy-duty operation.
  
• Remove paint from new sprockets before installation.
  
• Replace bolts if signs of thread stretch or corrosion appear.
  
• Use calibrated torque wrenches and follow OEM specifications.
  
• Inspect contact surfaces with a straightedge for flatness.
  

• Install torque-angle monitoring tools for critical fasteners.
  
• Use color-coded bolt kits to track replacements.
  
• Apply surface conditioning discs to mating areas before assembly.
  

Security System Overview
The Caterpillar 310 mini excavator incorporates an advanced security system designed to protect machinery from unauthorized use. This system often uses a numeric security code or passcode to enable startup. Typically, machines come factory-set with default codes, such as "1111," which operators may change for enhanced security.
Common Passcode Problems

• Users sometimes reset or disable security settings without fully understanding consequences.
  
• If the passcode is changed or disabled incorrectly, the machine may lock out, preventing startup.
  
• Default passcodes (like 1234 or the last four digits of the serial number) may no longer work after changes.
  
• Locked-out machines require authorized software access or dealer intervention to reset security codes.
  

• Security codes are linked to the machine's Engine Control Module (ECM) and operator interface.
  
• Modern Cat machines use electronic keys, Bluetooth keys, or numeric code pads to enhance security.
  
• Changing passcodes without backup or documentation can result in lockout, often requiring costly dealer service for reset.
  

• Operators have reported locked machines after disabling the security prompt in settings.
  
• Attempts to use common default codes including "1234," "9992," or serial number extensions often fail post-change.
  
• Dealer service visits may come with high charges (e.g., $960) for passcode recovery or ECM resets.
  
• Advice includes securely recording any new passcodes immediately and avoiding disabling the security system unless confident.
  

• Always document security code changes in a secure location.
  
• If locked out, contact authorized Caterpillar dealerships or certified technicians who can reset codes via official diagnostic tools.
  
• Avoid attempting unauthorized bypass methods which may void warranties or damage systems.
  
• In cases of frequent operator turnover, consider passcode management policies ensuring smooth transitions.
  

• ECM (Engine Control Module): Controls engine functions and security settings.
  
• Security Passcode: Numeric code required for machine startup authorization.
  
• Locked Out: State where machine refuses to start without correct passcode.
  
• Dealer Diagnostic Tools: Official software and hardware used to manage and reset machine codes.
  
• Bluetooth Key: Wireless electronic key replacing traditional ignition keys.
  

The JD 323E and Its Market Position
The John Deere 323E compact track loader was introduced in the early 2010s as part of Deere’s E-Series lineup, designed to meet Tier 4 emissions standards while improving operator comfort and hydraulic performance. With a rated operating capacity of 2,230 pounds and a tipping load of 6,400 pounds, the 323E was positioned as a mid-range machine ideal for grading, material handling, and attachment-driven tasks.
John Deere, founded in 1837, has long been a dominant force in agricultural and construction equipment. By the time the 323E entered production, Deere had already sold hundreds of thousands of compact loaders globally. The E-Series was developed to compete directly with offerings from Caterpillar, Bobcat, and Case, with emphasis on cab ergonomics, joystick control, and auxiliary hydraulic versatility.
Key Features and Configuration Options
The 323E came standard with electrohydraulic joystick controls, a pressurized cab with heat and air conditioning, and a vertical lift path for improved reach at full height. Buyers could configure the machine with a general-purpose bucket, pallet forks, or high-flow hydraulics for demanding attachments.
Terminology:

• Vertical Lift Path: A loader arm design that maintains a straight upward trajectory, ideal for truck loading and pallet handling.
  
• Electrohydraulic Joystick: A control system that uses electronic signals to actuate hydraulic valves, offering smoother and more precise operation.
  
• High-Flow Hydraulics: An optional system delivering increased fluid volume for attachments like mulchers, planers, and snow blowers.
  

• Track condition: Look for cracking, delamination, or excessive wear on the lugs.
  
• Hydraulic couplers: Check for leaks, corrosion, and proper engagement.
  
• Cab electronics: Test all switches, gauges, and joystick responsiveness.
  
• Engine compartment: Inspect belts, filters, and fluid levels for signs of neglect.
  
• Service history: Request maintenance records, especially for hydraulic fluid changes and filter replacements.
  

• Install a hydraulic quick coupler for faster attachment swaps.
  
• Add LED work lights for improved visibility in low-light conditions.
  
• Use foam-filled tires or track inserts for puncture resistance in demolition work.
  

• Smooth joystick control with minimal lag
  
• Strong lifting capacity for its size class
  
• Quiet cab with effective HVAC
  
• Reliable engine performance, especially with regular maintenance
  

• Change engine oil every 250 hours
  
• Replace hydraulic filters every 500 hours
  
• Inspect track tension monthly
  
• Clean radiator and oil cooler fins weekly in dusty environments
  

The Kobelco 250, a powerful and versatile tracked excavator, is widely used in construction, excavation, and demolition projects. However, like any piece of heavy machinery, it can experience issues that impact its performance. One of the common problems operators encounter with the Kobelco 250 is a weak left track. This issue can significantly affect the machine’s overall efficiency and may even lead to additional mechanical problems if not addressed promptly.
Overview of the Kobelco 250 Excavator
The Kobelco 250 is part of the SK-250 series of crawler excavators. Known for its durability, fuel efficiency, and advanced hydraulic technology, the SK-250 has been a popular choice for operators working in tough conditions. With a powerful engine and hydraulic system, the Kobelco 250 is capable of tackling heavy lifting and digging tasks.
The machine's crawler track system, which is crucial for mobility and stability, is composed of two independent tracks powered by hydraulic motors. These tracks are essential for the excavator to function efficiently, providing balance and enabling movement across uneven terrain.
What Causes Weak Tracks on the Kobelco 250?
When a weak left track is noticed, it typically points to a few potential issues within the system. These issues can stem from mechanical problems, hydraulic failures, or wear and tear on critical components. Understanding the possible causes is the first step in diagnosing the issue.
1. Hydraulic Motor Problems
The hydraulic motor powers the track system and ensures that both tracks move in unison. If the left track is weak, it may indicate a problem with the hydraulic motor on the left side.

• Solution: Inspect the hydraulic motor for signs of damage or wear. Check for leaks, unusual noises, or vibrations that could indicate a failing motor. A hydraulic motor that is not functioning properly may require a full replacement or repair.
  

• Solution: Check the hydraulic pump and valves for blockages, leaks, or damage. Ensure that the hydraulic fluid levels are correct and that there is no contamination. If the system is not delivering the correct amount of fluid, repairs or replacements may be necessary.
  

• Solution: Inspect the track tension on both sides. Ensure that the left track is properly tensioned according to the manufacturer’s specifications. If the track is too loose, adjust the tension; if it's too tight, loosen it slightly to allow for better movement.
  

• Solution: Check the final drive for any signs of damage or wear. Look for leaks in the drive assembly or unusual noises during operation. If the final drive is damaged, it may need to be repaired or replaced.
  

• Solution: Inspect both tracks for signs of wear, particularly the left side. If the track is excessively worn, it may need to be replaced. Regular maintenance, including track inspection and lubrication, can help extend the lifespan of the tracks.
  

• Solution: Inspect the drive sprocket and idlers for signs of damage or misalignment. If necessary, replace the damaged components to restore proper function.
  

• Solution: Ensure the hydraulic fluid is at the correct level and free of contaminants. If the hydraulic motor appears damaged, it may need to be replaced.
  

• Solution: Adjust the track tension according to the manufacturer’s specifications. Proper tension is crucial for the effective operation of the tracks.
  

• Solution: If the final drive is damaged, it may need to be rebuilt or replaced to restore the functionality of the tracks.
  

• Solution: Replace any excessively worn tracks to ensure the excavator operates efficiently and evenly.
  

• Solution: Replace any worn or damaged sprockets or idlers to restore proper track movement.
  

Engine and Power

• The John Deere 444E is powered by a 4-cylinder, 4.5-liter turbocharged diesel engine delivering approximately 95 to 100 horsepower.
  
• This engine balances fuel efficiency with power, enabling the loader to perform diverse heavy-duty tasks effectively.
  

• Equipped with a 4-speed powershift transmission featuring a torque converter for smooth shifting and power delivery.
  
• Hydraulic flow rates can reach up to about 39 gallons per minute, supporting various attachments and loader functions.
  
• Wet-disk power brakes with a parking brake system enhance braking performance for operator safety.
  

• Bucket capacities vary from 1.63 to 2.38 cubic yards, allowing flexibility for different materials and job types.
  
• Breakout force ranges from approximately 15,000 to 18,000 pounds, offering strong digging and pushing capability.
  
• Tipping loads range around 13,000 to 14,500 pounds depending on bucket and configuration, ensuring machine stability under load.
  

• Operating weight is roughly 19,000 lbs, providing ground stability with an articulated frame for tight turns.
  
• Overall length with bucket on ground is about 20 feet 8 inches.
  
• Width over tires measures approximately 7.3 feet, while height to cab top is near 10.4 feet.
  
• Ground clearance close to 1.4 feet enhances maneuverability on uneven terrain.
  

• ROPS-certified cab with canopy improves operator safety and comfort.
  
• Available outfitted with either manual or optional hydraulic quick coupler systems, improving attachment changes.
  
• Controls include single or dual lever options with features such as automatic return-to-dig and boom height control.
  

• Inboard planetary final drives provide robust drivetrain durability.
  
• Extensive parts availability and rapid shipping support minimize downtime.
  
• Operator and maintenance manuals provide guidance for troubleshooting and preventive maintenance.
  

• Tipping Load: Maximum load before stability loss occurs.
  
• Breakout Force: Force bucket applies to penetrate or move material.
  
• Powershift Transmission: Transmission with automatic clutch engagement for smooth shifts.
  
• Wet-Disc Brakes: Braking system immersed in oil for cooling and durability.
  
• Quick Coupler: Attachment system allowing rapid, tool-free swaps.
  
• ROPS: Rollover Protective Structure for safety.
  

The John Deere 160C, a mid-sized crawler excavator, has been a trusted workhorse for construction, demolition, and excavation tasks. However, like all machinery, the 160C may encounter issues from time to time, with one of the most concerning being the illumination of the engine warning light on the dashboard. This indicator can be triggered for a variety of reasons, and understanding the underlying causes, as well as how to address them, is crucial for maintaining the machine’s performance and avoiding costly repairs.
History of the John Deere 160C
The John Deere 160C is part of the C-Series of excavators, known for their robust design and reliability. Introduced in the early 2000s, these machines were developed to offer a balance between power, efficiency, and operator comfort. With its powerful engine and advanced hydraulics, the 160C has been widely used in applications ranging from heavy-duty digging to fine grading work.
The C-Series models, including the 160C, were designed with a focus on fuel efficiency, ease of maintenance, and lower emissions. These machines became popular in the market due to their solid construction and adaptability to various tasks, offering both smooth performance and long-lasting durability in demanding environments.
What Does the Engine Warning Light Indicate?
The engine warning light on a John Deere 160C is an essential part of the machine’s diagnostic system. It is designed to alert the operator when something is wrong with the engine, transmission, or other critical systems. While the exact cause of the warning light can vary, it typically signals an issue that requires attention to avoid further damage to the engine or related components.
The engine warning light can be triggered by a variety of factors, including:
1. Low Engine Oil Pressure:
Low engine oil pressure is one of the most common causes of the engine warning light illuminating. If the oil pressure drops too low, it can lead to insufficient lubrication of the engine components, causing excessive wear or even failure.

• Solution: Check the engine oil level and top it off if necessary. If the oil level is fine, consider changing the oil filter or inspecting for oil leaks.
  

• Solution: Check the coolant level and top it off if needed. Inspect the cooling system for leaks, and ensure the radiator is clean and free from debris.
  

• Solution: Inspect and replace the fuel filter if it is clogged. Check the fuel pump and lines for any signs of damage. Use high-quality diesel fuel to avoid contamination.
  

• Solution: Inspect all wiring and electrical connections for signs of wear, corrosion, or loose connections. Check the battery and alternator for proper function.
  

• Solution: Regularly inspect and clean or replace the air filter to ensure optimal airflow to the engine.
  

• Solution: Use a diagnostic tool to retrieve the error codes from the machine’s onboard computer. This will help pinpoint the specific issue, whether it’s related to the engine, transmission, fuel system, or electrical components.
  

• Solution: Ensure the fluids are at the proper levels and replace any dirty or clogged filters.
  

• Solution: Repair any leaks and ensure all connections are secure. Clean any debris or dirt buildup that could affect performance.
  

• Solution: Check the alternator output and ensure the battery is fully charged. Inspect the wiring and connectors for any signs of damage.
  

Overview
The Caterpillar 246C is a compact skid steer loader equipped with a driver alert system designed to notify operators of machine issues and safety warnings. Sometimes, operators experience a problem where the driver alert light activates, preventing the machine from starting or cranking, causing operational delays.
Common Symptoms

• Battery voltage appears normal (e.g., ~13 volts after charging).
  
• Machine powers on with electrical systems active.
  
• Driver alert light illuminates continuously.
  
• Engine fails to crank or start despite apparent electrical power.
  

• Battery or Electrical System Issues: Even with a good voltage reading, battery health or wiring faults could cause warning signals.
  
• Faulty or Stuck Driver Alert System: The alert module may detect faults in sensors or system components, triggering shutdown as a safety feature.
  
• Interlock or Safety Switch Engagement: Certain protective switches (e.g., door switches, parking brake) may prevent engine start if improperly engaged.
  
• ECM (Engine Control Module) Faults: Malfunctions in the ECM or communication faults with components may result in start lockout.
  
• Sensor Failures: Engine temperature, oil pressure, or hydraulic sensors not providing correct signals can trigger alert states.
  
• Fuse or Relay Problems: Blown fuses or bad relays interrupting startup circuit.
  

• Verify battery condition via load and cranking amps testing.
  
• Inspect all wiring harnesses for damaged or corroded connections.
  
• Check operator safety switches such as seat belt sensor, door interlocks, and parking brake.
  
• Scan ECM for fault codes using Caterpillar diagnostic tools or compatible readers.
  
• Inspect fuses and relays related to ignition and engine control.
  
• Reset driver alert system if possible following machine-specific procedures.
  

• Regular electrical system inspections during scheduled maintenance.
  
• Ensuring all safety switches are clean, properly adjusted, and functioning.
  
• Following manufacturer-recommended diagnostic procedures when alert light activates.
  
• Keeping updated with software or firmware revisions for ECM.
  

• Driver Alert System: Monitor warning system alerting operator of faults or hazards.
  
• ECM (Engine Control Module): Electronic unit controlling engine management functions.
  
• Interlock Switch: Safety device preventing operation under unsafe conditions.
  
• Fuse and Relay: Electrical components that protect or switch circuits.
  
• Diagnostic Trouble Codes (DTCs): Stored fault codes used in troubleshooting.
  

The Oliver OC-4 crawler tractor, originally produced in the mid-20th century, remains a popular choice for collectors and heavy equipment enthusiasts. Known for its rugged design and durability, the OC-4 was widely used in farming, construction, and utility work. Like any vintage machinery, maintaining the OC-4 involves understanding the specific oils and lubricants required for optimal performance, particularly when it comes to its differential brake system. This guide provides an in-depth look at the recommended oil for the differential brake of the Oliver OC-4, its importance, and tips on maintaining your machine.
History of the Oliver OC-4
The Oliver OC-4 was manufactured by the Oliver Corporation, which was well-known for producing tractors and other agricultural machinery. Produced between the 1940s and 1960s, the OC-4 was part of the Oliver 4-series crawler tractors. The OC-4 was built with a diesel engine, designed for tough tasks like heavy-duty plowing, road building, and excavation. Over time, it became a popular choice in many industries, and even today, enthusiasts appreciate its vintage design and reliable performance.
The OC-4 was a versatile machine, often used in tough agricultural conditions but also capable of handling construction and industrial workloads. Its simple design made it easy to repair and maintain, a characteristic that has allowed it to endure in the used equipment market even decades after production ceased.
Importance of the Differential Brake System
The differential brake on the Oliver OC-4 plays a critical role in controlling the movement and steering of the crawler tractor. As with other track-driven machines, the OC-4 uses the differential brake to manage the machine’s turning radius and provide greater maneuverability, especially in tight spaces.
The differential brake system works by applying pressure to the brakes on one side of the machine, allowing it to pivot around the opposite side. When properly maintained, the system ensures smooth operation, reduces wear and tear on other components, and improves the overall efficiency of the vehicle. However, to keep the differential brake working optimally, choosing the right oil and maintaining it regularly is essential.
What Oil Should Be Used for the Differential Brake?
For the differential brake system of the Oliver OC-4, it is crucial to select the correct type of oil. The oil plays a key role in ensuring smooth brake function and preventing overheating or excessive wear. Here are the important considerations when choosing oil for this component:
1. Type of Oil:
For the differential brake of the OC-4, a high-quality, heavy-duty gear oil is recommended. Specifically, oils with an SAE 90 or 80W-90 viscosity grade are typically used. These oils offer the right balance of lubrication and resistance to pressure, ensuring that the differential brake components remain protected under the demanding loads of operation.

• Recommended Oil: SAE 90 or 80W-90 gear oil.
  
• Oil Additives: Consider oils with limited-slip additives to help prevent wear on the friction plates.
  

• Synthetic Oil: Provides better stability and high-temperature performance.
  
• Conventional Oil: Generally sufficient for older machines, as it is less likely to damage vintage components.
  

• Oil Change Frequency: Every 500 to 1,000 hours.
  
• Signs of Oil Contamination: Darkening of the oil, increased noise or vibration from the differential.
  

• Solution: Drain old oil, inspect brake components for wear, replace seals if necessary, and refill with the correct oil.
  

• Solution: Use the correct oil viscosity and ensure that oil levels are maintained. If overheating persists, inspect the brake components for damage or excessive wear.
  

• Solution: Inspect seals and gaskets regularly, and replace any that appear worn or damaged. Ensure the housing is free from cracks and other damage.
  

• Regularly check oil levels and ensure that the correct oil is used in the differential brake.
  
• Inspect the brake components (shoes, drums, and seals) for wear and replace them as necessary.
  
• Replace the oil filter if your OC-4 is equipped with one to ensure clean oil circulates through the system.
  
• Perform oil changes on time, especially if the tractor is used in harsh conditions like wet or muddy environments.
  
• Test the brake system periodically by engaging the differential brakes and checking for smooth operation.
  

Machine Description
The Komatsu RC-100, also known as the PC 100 series excavator, is a well-regarded medium-sized excavator designed for a broad range of construction and excavation work. It is favored for its balance of power, hydraulic efficiency, and versatility in digging, lifting, and demolition tasks.
Engine and Power

• Equipped with an engine delivering approximately 81 horsepower, providing sufficient power for heavy-duty site work.
  
• The engine complies with industry standards for fuel efficiency and emissions, supporting longer operational cycles.
  

• The hydraulic system features a maximum flow rate close to 248 liters per minute, ensuring smooth boom and bucket operation.
  
• Relief valve pressure is typically around 2,500 psi, managing hydraulic pressures within safe and efficient limits.
  

• Operating weight stands near 11,100 kilograms (about 24,460 pounds), balancing stability with mobility.
  
• Track gauge is roughly 1,960 mm and track length about 3,300 mm, contributing to stability during digging and lifting operations.
  
• Overall machine length measures approximately 7,170 mm with a tail swing radius around 2,130 mm aiding in maneuvering confined spaces.
  

• Maximum digging depth reaches up to 5,000 mm, supporting a variety of excavation depths.
  
• Bucket capacity is approximately 0.67 cubic meters, ideal for medium-scale earthmoving tasks.
  
• The lifting capacity is roughly 5,300 kilograms, enabling effective material handling.
  

• The fuel tank capacity holds about 230 liters, supporting extended jobsite activity with fewer refueling stops.
  
• Hydraulic tank capacity of about 145 liters (with 100 liters in the hydraulic oil tank) ensures ample fluid for sustained hydraulic performance.
  
• Regular maintenance points are accessible for quick service and reduce machine downtime.
  

• The RC-100 suits construction, site development, trenching, and demolition.
  
• Its dimensions and power make it effective in urban or confined areas requiring precise operation.
  
• Often chosen for jobs requiring a blend of excavating strength and maneuverability.
  

• Track Gauge: Distance between the left and right tracks influencing stability.
  
• Hydraulic Flow Rate: The volume of hydraulic fluid delivered to the actuators per minute.
  
• Relief Valve Pressure: Safety limit controlling maximum hydraulic pressure.
  
• Operating Weight: Total machine weight including fluids and attachments.
  
• Tail Swing Radius: The distance the rear of the machine moves during rotation.