A forestry contractor reported that a John Deere 210G LC excavator took 5 seconds to curl the bucket when digging in heavy clay. When the operator tried to curl the bucket, the engine RPM dropped by 300 RPM before recovering.
The technician checked the "Main Pump Pressure" and found it reached the relief pressure of 340 bar, but the flow was low. He focused on the "Bucket Control Valve Block." The bucket circuit uses a "Regeneration Orifice" to allow oil from the rod side to bypass to the piston side for fast curling. He removed the "Bucket Spool End Cap." He found the "Regeneration Orifice" (a small brass jet) was completely blocked by a piece of sealing tape from a previous repair. The blockage forced all the oil through the main spool, causing a severe flow restriction and hydraulic lock.
The "Engine Stumble" was caused by the "Pilot Pump." He tested the pilot pressure at the bucket joystick port. The pressure was 20 bar instead of the specified 40 bar. The pilot pump is a small gear pump attached to the main pump. He removed the pilot pump housing. The "Drive Gear" had sheared off its splines due to a lack of lubrication. The pilot pump was running at 50% capacity, delaying the opening of the main bucket spool, which compounded the flow restriction.
The repair involved clearing the regeneration orifice, replacing the pilot pump assembly, and flushing the system. After reassembly, the bucket curled instantly with no engine stumble.
