3978818 XCMG GR2605 motor grader crankshaft bearing

Technical Parameters

• Part No.：3978818 (C3978818), Upper Main Bearing
• Brand：Cummins / DCEC
• Type：Crankshaft Main Bearing, STD Size
• Material：Steel-backed Al-Sn alloy
• Dimensions：Standard ID φ76.2mm, Width 30mm, Thickness 3mm
• Lubrication：Center oil hole & distribution groove
• Hardness：Alloy HV 35-45, Steel back HRB 85-95
• Fit Engines：4BT3.9, 6BT5.9, ISBE, ISDE, QSB6.7, B5.9
• Qty：6 per engine (upper)
• Pair Lower：3978820
• Thrust Bearing：3978822
• Cross：3929016 (old No.)

Application Scenarios

• Engines：4BT3.9, 6BT5.9, ISBE, ISDE, QSB6.7, B5.9
• Vehicles：Dongfeng Kinland, Tianjin, 153, Duolika
• Machinery：1–3.5T loaders, excavators, bulldozers, rollers
• Gensets：50–150kW diesel generators
• Location：Cylinder block upper main saddles, 1–6 journals
• Function：Friction reduction, load support, crankshaft alignment

Common Faults & Troubleshooting

1. Wear & Bearing Burnout

• Cause：Insufficient oil, clogged galleries, contamination, overload
• Symptom：Alloy flaking, journal scoring, noise, low pressure
• Fix：Replace 3978818+3978820 set; clean galleries; new oil/filter

2. Alloy Spalling & Chipping

• Cause：Fatigue, heat softening, shock, improper clearance
• Symptom：Localized failure, debris, wear
• Fix：Install OEM 3978818; inspect journal roundness; set 0.05–0.10mm clearance

3. Scoring & Scratching

• Cause：Contaminants, assembly dirt, rough journals, misalignment
• Symptom：Axial scratches, noise
• Fix：Flush lubrication system; polish journals; align properly