Komatsu/17A-30-48461/D155 Track Tensioning Cylinder Assy
Product Specifications
Komatsu D155A6 Dozer Track Tensioning Cylinder Assembly: A Comprehensive Overview
The Tension Cylinder Assembly, commonly referred to as the Track Tensioning Cylinder or Hydraulic Track Adjuster, is a critical component on the undercarriage of the Komatsu D155A6 bulldozer. Its primary function is to maintain the correct tension (tightness) in the track chain, which is essential for the machine's performance, efficiency, and longevity.
1. Function and Purpose
The tension cylinder serves two main purposes:
Maintain Optimal Track Tension: It applies a precise amount of force to the idler (front idler wheel), pushing it forward to take up slack in the track chain. Correct tension prevents:
Derailment: Loose tracks can easily jump off the rollers and sprockets.
Excessive Wear: Both loose and overtightened tracks cause accelerated wear to the track chain, links, bushings, sprockets, and rollers. Loose tracks can "whip" and cause impact damage, while tight tracks increase friction and heat.
Loss of Efficiency: A loose track consumes more power due to internal slippage and reduces traction and pushing power.
Increased Fuel Consumption: The engine works harder to overcome the inefficiencies of a poorly tensioned track.
Act as a Shock Absorber: The assembly incorporates a pre-charged nitrogen gas chamber that acts as a spring. It allows the idler to move rearward slightly when the track hits an obstruction (e.g., a rock or log), absorbing the impact shock. This protects the entire undercarriage and mainframe from excessive stress and potential damage.
2. Key Components of the Assembly (Assy)
The assembly is more than just a cylinder; it's an integrated system. Its main components are:
Cylinder Barrel: The main body that houses the piston and contains the hydraulic fluid.
Piston and Piston Rod: The rod is connected to the idler. Hydraulic pressure pushes the piston forward to tension the track.
Grease Fitting (Zerk Fitting): The point where a grease gun is attached. Grease is used as the hydraulic medium to push the piston.
Check Valve (Grease Valve): A one-way valve that allows grease to be pumped into the cylinder but prevents it from flowing back out. This locks the tension in place.
Release Valve (Pressure Release Valve): A bleeder valve that, when loosened, allows grease to be released from the cylinder, thereby reducing track tension for maintenance or track removal.
Nitrogen Gas Chamber (Accumulator): A sealed chamber separated from the hydraulic (grease) side by a floating piston or diaphragm. This chamber is pre-filled with dry nitrogen gas to a specific pressure.
3. Location on the Komatsu D155A6
The D155A6 has two tension cylinder assemblies—one for each track. They are located at the front of the undercarriage, inside the track frame, and are directly connected to the front idler. The piston rod pushes against the idler yoke, which moves the idler forward or backward.
4. Operation and Working Principle
The operation is a elegant combination of hydraulics (grease) and pneumatics (nitrogen):
Tensioning (Adding Grease):
To increase tension, a grease gun is attached to the grease fitting.
As grease is pumped in, it forces the hydraulic piston forward.
The piston rod pushes the idler forward, stretching the track chain and removing slack.
The check valve closes, trapping the grease and holding the idler in its new position.
Shock Absorption:
When the track encounters a large obstacle, the force tries to push the idler backward.
This force is transferred to the piston, which pushes against the column of grease.
The grease, being incompressible, transfers this force to the floating piston.
The floating piston compresses the nitrogen gas in the accumulator chamber. Nitrogen is compressible and acts like a spring, absorbing the energy of the impact.
Once the obstacle is passed, the expanding nitrogen gas pushes the floating piston back, returning the idler to its original position.
De-tensioning (Releasing Grease):
For track removal, repair, or to reduce overtightening, the release valve is slowly loosened.
This allows grease to escape, which lets the nitrogen gas pressure push the idler rearward, relaxing the track tension.
Caution: This must be done slowly and carefully as hot, high-pressure grease can be ejected violently.
5. Importance of Nitrogen Gas Charge
The nitrogen pre-charge is a critical specification. Using compressed air is strictly prohibited because:
Moisture: Air contains moisture that can cause internal corrosion and, in freezing conditions, ice formation which can lock up the cylinder.
Oxygen: The oxygen in air supports combustion, creating a fire hazard if a leak occurs near a hot surface and the oil/grease ignites.
Consistency: Nitrogen provides a stable, inert, and predictable medium for shock absorption.
6. Common Failure Modes and Symptoms
Loss of Nitrogen Charge: The most common failure. Symptoms include a very stiff track with no shock absorption (the track feels "tight" all the time) and the idler won't move when hitting obstacles, leading to a harsh ride and potential damage.
Worn Seals: Leaking grease from the cylinder rod or a leaking check/release valve indicates failed seals, leading to an inability to hold tension.
Damaged Cylinder Rod: Scratches or scoring on the polished rod surface will damage seals and cause leaks.
Stuck or Clogged Valves: The check valve can become clogged with hardened grease, preventing tensioning.
7. Maintenance and Servicing
Regular Inspection: Check track tension daily according to the operator's manual (typically measuring sag at the top of the track between the carrier roller and the sprocket).
Correct Tensioning: Always use high-quality, high-pressure grease. Pump grease in small increments and measure sag frequently to avoid overtightening.
Nitrogen Recharge: If shock absorption is lost, the assembly must be removed and serviced by a qualified technician. The nitrogen chamber must be recharged to Komatsu's specified pressure (which requires special tools and safety procedures).
Seal Replacement: If grease is leaking, the assembly should be rebuilt with a genuine Komatsu seal kit to ensure compatibility and longevity.
Regular Inspection: Check track tension daily according to the operator's manual (typically measuring sag at the top of the track between the carrier roller and the sprocket).
Correct Tensioning: Always use high-quality, high-pressure grease. Pump grease in small increments and measure sag frequently to avoid overtightening.
Nitrogen Recharge: If shock absorption is lost, the assembly must be removed and serviced by a qualified technician. The nitrogen chamber must be recharged to Komatsu's specified pressure (which requires special tools and safety procedures).
Seal Replacement: If grease is leaking, the assembly should be rebuilt with a genuine Komatsu seal kit to ensure compatibility and longevity.
