Diesel Engine Parts, Products

1. Product Specifications

• Part Number: 3942749 (Cross-reference: 3964713, 5253888)
• Applicable Engines: Cummins 6CT8.3, QSC8.3, QSL9, ISL 8.9L diesel engines
• Material: High-strength forged steel / ductile iron, heat-treated for wear resistance and durability
• Type: Exhaust rocker arm (lever-style, single-arm)
• Key Dimensions (Typical):
  • Bore diameter (for rocker shaft): Approx. 22 mm
  • Valve stem contact end: Rounded, hardened surface
  • Pushrod contact end: Screw-adjustable ball socket for valve lash setting
• Weight: Approx. 1.2–1.5 kg
• Condition: 100% new OEM/aftermarket replacement
• Warranty: 1 year
• 2. Installation Position
• Location: Mounted on the cylinder head of the engine, inside the rocker arm housing (valve cover area).
• Mounting: Pivots on a rocker shaft (common shaft for all rocker arms).
• End Connections:
  • One end: Contacts the exhaust valve stem tip.
  • Other end: Actuated by a pushrod (from the camshaft lifter).
• Orientation: Positioned above the exhaust valves; in Cummins QSC/ISL engines, it is the shorter rocker arm (distinct from the longer intake rocker arm).
• 3. Function
• Core Role: A lever in the valvetrain that transfers and amplifies motion from the camshaft to the exhaust valves.
• Working Principle:
  1. The camshaft rotates, lifting a pushrod upward.
  2. The pushrod pushes one end of the rocker arm, which pivots on the rocker shaft.
  3. The opposite end presses down on the exhaust valve stem, opening the exhaust valve against spring pressure.
  4. As the camshaft rotates further, the pushrod lowers; the valve spring closes the exhaust valve, and the rocker arm returns to its rest position.
• Key Functions:Timed Exhaust Gas Release: Opens exhaust valves at the correct moment in the 4-stroke cycle to expel burned gases from combustion chambers. Motion Conversion: Converts the camshaft’s rotational motion into linear (up/down) valve motion. Leverage Amplification: Increases cam lift to achieve sufficient exhaust valve opening (lift) for optimal flow. Valve Lash Adjustment: Equipped with an adjustment screw to set and maintain proper clearance (lash) between the rocker arm and valve stem.