A highway contractor reported that a BOMAG BW 213 D-5 single-drum vibratory roller had developed a progressive loss of compaction effectiveness over a two-week period. The operator noticed that the machine's characteristic "hum" during compaction passes had become noticeably quieter, and the drum's vibration felt weaker underfoot. Soil that had previously been compacted in four passes now required six or more passes to achieve the same dry density. The front drum's bearing area also ran hot to the touch after extended operation, and a thin film of gear oil was visible around the drum's drive-side bearing housing.
The technician first understood the BW 213 D-5's vibratory drum architecture. The drum contains an "Eccentric Shaft" - a shaft with an off-center weight mass mounted at its center, rotated by a "Drum Vibration Motor" (a hydraulic piston motor mounted inside or adjacent to the drum). As the eccentric shaft rotates, the off-center mass generates the centrifugal force that produces the drum's vibratory compaction action. The eccentric shaft is supported on "Drum Bearings" - large heavy-duty spherical roller bearings housed in bearing blocks at each end of the drum. The drum's interior is partially filled with "Drum Oil" - a specified gear oil that lubricates the bearings and the vibration motor's drive coupling.
He checked the drum's oil level through its inspection plug - the oil level was well below specification, and the oil that drained out was dark and contained visible metallic particles. This indicated the drum's internal lubrication had been failing for some time. He then ran the machine with the vibration function activated and used an infrared thermometer to measure the drum's bearing-housing temperatures. The drive-side bearing housing reached 95°C after 10 minutes of operation (spec maximum is roughly 70°C), confirming bearing distress.
He removed the drum's drive-side bearing housing cover to inspect the bearing. The "Drum Bearing" showed severe distress - the spherical rollers showed flat-spotting and pitting, the raceways showed visible scoring, and the bearing's cage had deformed. The "Drum Vibration Motor Shaft Seal" - the rotary seal that prevents the vibration motor's gear oil from leaking into the drum's bearing cavity - had failed, allowing gear oil to leak out of the drum over time and allowing dust and moisture to migrate in, contaminating the bearings.
The root cause was traced to drum vibration motor shaft seal failure, compounded by missed drum-oil level checks. Drum vibration motor shaft seals are subjected to continuous rotational contact, high temperatures during extended compaction cycles, and to the vibration-induced flexing of the motor shaft during operation. Over extended service, the seal's elastomer had hardened and cracked, eventually failing. The leaking drum oil had reduced internal lubrication, causing bearing distress and the overheating the operator described.
The repair involved replacing both drum bearings with new units, replacing the drum vibration motor's shaft seal with a new unit, thoroughly flushing the drum's interior to remove metallic debris and contaminated oil, and refilling the drum with the specified drum gear oil to the correct level. The vibration motor's internal components were inspected (pistons and cylinder block in good condition), and the motor was reassembled with fresh lubricant. After reassembly and a test cycle, the drum's vibration amplitude was verified with a compaction meter to be within specification, the drum's bearing-housing temperature stabilized at 62°C during a 30-minute loaded test, and no further oil seepage was observed. Drum-oil level checks were added to the machine's 50-hour service checklist, and drum vibration motor shaft seal inspection was added to the annual inspection.
