Track Adjuster Assy 9271451 For Hitachi EX1200-6

A: This problem is often related to seal failure, component loss, or abnormal pressure in the tensioner assembly. You can troubleshoot it by following the steps below:
Check the seal assembly and cylinder for leaks: Observe the connection between the tensioning cylinder piston rod and the housing for signs of grease leakage. If there is leakage, it is usually due to aging or damage of the piston seal, resulting in grease loss in the high-pressure chamber and inability to maintain tension.
Check the buffer spring condition: If no obvious leakage is found, disassemble and inspect the buffer spring for fatigue fracture, deformation, or elasticity loss. Spring failure will directly lead to insufficient preload, especially after heavy load operation, the track will easily loosen quickly.
Check for one-way valve failure: If the tensioner plunger feels "soft" when pressed (can be pushed easily without resistance) and there is no leakage, the one-way valve built into the cylinder may have failed, causing the high-pressure chamber to be connected to the low-pressure chamber, and the grease cannot maintain pressure. The one-way valve component needs to be disassembled and replaced.

A:Inspection and adjustment steps:
Preparation: Park the equipment on a flat and hard ground, turn off the engine and apply the parking brake, safely lift the track side machine body with a jack, and remove the track frame side cover to expose the tensioner assembly.
Tension check: Measure the droop in the middle of the track, or press the middle of the track. For Hitachi EX1200, it is usually appropriate for the track to be lifted 25-30mm. Please refer to the equipment operation manual for the specific value. You can also measure the gap between the track and the sprocket. The normal range is 5-15mm.
Adjustment operation:
When the track needs to be tightened: use a grease gun to inject grease into the tensioner oil filling valve and push the cylinder piston rod out until the standard tension is reached.
When the track needs to be loosened: use a wrench to slowly loosen the drain valve counterclockwise (1-1.5 turns are enough), and tighten the drain valve after the grease is slowly discharged and the track is relaxed to the target state.

A: The most easily overlooked risk is the release of tension from the high-pressure buffer spring. The buffer spring in the tensioner assembly is always highly compressed during operation, storing enormous elastic potential energy. If forcibly disassembled, the spring could instantly pop out, causing serious injury or component damage.

Safe handling methods: Release pressure in advance: Before disassembly, the grease in the cylinder must be completely drained through the oil drain valve to release the hydraulic pressure; for spring preload, the tensioner assembly must be removed as a whole, and the spring must be slowly compressed using a special press. After the tension is completely released, the restraining parts such as the fixing pin or flange can be removed. Professional tools and personnel operation: It is strictly forbidden to use tools such as hammers and crowbars for violent disassembly. The operation must be performed by qualified maintenance personnel using matching tooling (such as spring compressors).

A: Track frequently loose: Often due to hydraulic cylinder seal damage and grease leakage, buffer spring failure, or internal check valve malfunction that cannot maintain pressure;
Piston action stuttering: May be caused by impurities entering the mating surface, parts tolerance exceeding specifications, or mating surface scoring and wear;
Buffer spring failure: Common issues include fatigue fracture and deformation, leading to inability to cushion impact or provide pre-tension force;
Lubricant leakage: Besides damaged hydraulic cylinder seals, loose seals on the oil injection valve and oil drain valve can also cause this.