Cummins QSL Connecting Rods & Bearing Sets

The Cummins QSL engine is a powerful mid-range diesel platform that has earned a reputation for long service life, durability, and efficiency in both marine and industrial applications. A critical part of that reliability comes from the connecting rod assemblies and rod bearings that transfer combustion force from the piston to the crankshaft. Without properly fitted and well-maintained connecting rods, the engine’s performance and longevity can be compromised.

At Diesel Pro Power, trusted by over 40,000 satisfied customers worldwide, we provide a complete catalog of connecting rods, rod bearings, and related hardware for Cummins QSL engines. Our inventory includes standard-size bearing sets, oversize bearings for rebuilt crankshafts, and OEM-quality connecting rod bolts designed to withstand the stress and heat of high-output diesel operation.

This section serves as a comprehensive reference and buying guide for Cummins QSL connecting rod parts, designed to help operators, mechanics, and fleet managers make the right choice for every rebuild, repair, or preventative maintenance job.

The Role of Connecting Rods in Cummins QSL Engines

The connecting rod is one of the hardest-working components inside a diesel engine. Each rod links a piston to the crankshaft, converting the up-and-down motion of combustion into the rotational force that drives the engine’s output shaft.

In the QSL series, connecting rods must withstand extreme levels of stress:

• High combustion pressure from turbocharged operation.

• Thermal cycling caused by continuous load variations in marine propulsion, power generation, or industrial duty cycles.

• Shear and bending forces as the crankshaft rotates under torque loads.

To maintain this strength, Cummins QSL rods are manufactured from high-strength forged steel and paired with precision-machined bearing surfaces. These bearings provide the smooth, low-friction interface required for reliable operation over thousands of hours.

Bearing Sets for Cummins QSL Engines

Properly fitted bearing shells are essential to prevent excessive wear between the connecting rod and the crankshaft journal. Cummins designed multiple bearing sizes to accommodate new builds, rebuilds, and re-machined crankshafts.

Standard Size Bearing Sets

Standard-size bearing sets are used in engines with crankshafts that remain within original factory tolerances. These consist of an upper and lower bearing shell that service one connecting rod.

• Designed for new or lightly used crankshafts.

• Provide excellent oil film retention for long service life.

• Ideal for standard rebuilds where machining is not required.

Oversize 0.25 mm Bearing Sets

When crankshafts are re-ground to remove scoring or wear, an oversize bearing set is required. The 0.25 mm oversize bearing set allows mechanics to pair a newly machined journal with precision-fit shells, restoring original oil clearance.

• Suited for engines undergoing light to moderate crankshaft reconditioning.

• Maintains factory oil clearance tolerances.

• Ensures proper lubrication film under all load conditions.

Oversize 0.50 mm Bearing Sets

For crankshafts that require more extensive machining, the 0.50 mm oversize bearing set is available. This allows the QSL engine to remain in service even after heavier wear or damage has been corrected.

• Built for severely worn crankshafts that have been ground undersize.

• Provides full restoration of connecting rod bearing surfaces.

• Extends the usable life of major components, reducing replacement cost.

Connecting Rod Bolts & Cap Screws

Every Cummins QSL connecting rod is secured with high-tensile cap screws, sometimes referred to as connecting rod bolts. These fasteners hold the rod cap tightly to the rod body, ensuring consistent clamping force around the bearing shells.

• Manufactured from heat-treated alloy steel.

• Designed to resist stretching and fatigue failure under repeated high load cycles.

• Must be replaced during every major overhaul to maintain proper bolt stretch and torque retention.

Neglecting to replace rod bolts during a rebuild can lead to bearing cap separation, catastrophic bearing failure, or crankshaft damage. Diesel Pro Power stocks genuine-quality bolts that meet or exceed Cummins specifications for the QSL series.

Common Causes of Connecting Rod Wear in Cummins QSL Engines

Even with proper lubrication, Cummins QSL connecting rods and bearings face wear over time. Understanding these causes helps mechanics make informed choices when servicing or rebuilding engines.

1. Oil Contamination
   Dirt, soot, or fuel dilution can break down the oil film protecting bearings. This causes scuffing and eventual bearing failure.

2. Improper Torqueing of Rod Bolts
   Incorrect torque or reuse of overstretched bolts can result in cap movement, leading to uneven bearing wear.

3. Overheating
   High operating temperatures can reduce oil viscosity, allowing metal-to-metal contact between bearings and crank journals.

4. Excessive Engine Loads
   Continuous overloads in marine propulsion or generator sets place additional stress on connecting rods, accelerating fatigue.

5. Inadequate Rebuild Practices
   Skipping replacement of bearings or bolts during overhauls often leads to premature failures.

Best Practices for Servicing Cummins QSL Connecting Rods

To maximize engine life, Cummins and Diesel Pro Power recommend strict adherence to OEM service proceduresduring rebuilds:

• Always inspect crankshaft journals for scoring, taper, or out-of-round wear before selecting bearing size.

• Replace bearings as sets—never mix new with old.

• Install new connecting rod bolts with proper torque sequence and angle.

• Check oil clearance with plastigage to confirm correct fit.

• Pre-lubricate bearings before engine startup to avoid dry friction.

• Balance rods during rebuilds to maintain even firing smoothness.

Applications of Cummins QSL Engines

The QSL platform powers a wide variety of marine and industrial applications where durability is critical. Its 9-liter displacement and 4-valve per cylinder design make it a favorite for operators requiring a balance of torque and fuel economy.

Marine Applications

• Commercial fishing vessels.

• Workboats and tugboats.

• Ferries and passenger transport vessels.

• Recreational yachts requiring mid-range marine diesel power.

Industrial & Power Generation Applications

• Stationary power generators.

• Construction equipment including cranes and excavators.

• Agricultural machinery.

• Oilfield and mining support vehicles.

In all these roles, reliable connecting rods and bearing assemblies ensure that the QSL engine can operate under continuous load without failure.

Why Choose Diesel Pro Power for QSL Connecting Rod Parts?

When it comes to sourcing Cummins QSL connecting rod bearings and hardware, operators need more than just parts—they need a trusted supplier who can ensure accuracy, quality, and global delivery.

Diesel Pro Power offers:

• OEM-equivalent quality bearings and bolts.

• Worldwide shipping for marine and industrial operators.

• Expert technical support to assist with part selection.

• A proven track record with over 40,000 satisfied customers.

Every component is backed by our commitment to durability, precision, and long service life.