A contractor reported a disturbing, loud metallic clunking noise coming from the undercarriage of a SANY SY215C excavator. The noise occurred every time the upper structure swung past the 90-degree position on either side. The operator initially suspected a failing swing bearing or a loose counterweight bolt.
The technician inspected the swing bearing by measuring the backlash (gear clearance) and checking the mounting bolts, all of which were tight. The counterweight mounting points were also secure. The noise seemed to be coming from the track frame area. The technician then examined the track tensioning system.
The SY215C uses a grease-type track adjuster with a large recoil spring to absorb shock. The adjuster yoke, which holds the front idler, is bolted to the track frame. Upon close inspection, the technician found that the two large bolts securing the adjuster yoke were sheared, and the remaining bolts had stretched. The recoil spring assembly was slightly loose within its housing.
When the excavator swung, the centrifugal force caused the heavy recoil spring assembly to shift laterally inside the frame, hitting the side of the track frame rail. The cyclic nature of the noise (linked to the swing) was due to the momentum shift. The "metal-on-metal" sound was the spring housing impacting the frame.
The repair involved extracting the broken bolts and tapping new threads. High-strength grade 12.9 bolts were used with thread-locking compound. The adjuster was re-torqued to the specified high tension. The track tension was then readjusted using grease. Upon retesting, the clunking noise was completely eliminated.
