Cummins QSB 4.5 Connecting Rod Parts & Components

The connecting rod assembly is a critical link in your Cummins QSB 4.5 engine, transferring the linear motion of the piston into the rotational motion that powers your vessel or equipment. Maintaining these components to factory specifications is essential for performance, durability, and reliability—especially in demanding marine and industrial applications where the QSB 4.5 excels.

Below you’ll find a detailed overview of connecting rod components available for the QSB 4.5 platform, including bearings, bushings, and cap bolts. This section also covers the difference between fractured and non-fractured rod designs, standard and oversize bearing options, and key considerations when servicing or rebuilding your engine.

Bearing Sets for Cummins QSB 4.5 Connecting Rods

Standard Size Bearings for Non-Fractured Rods

Standard-size connecting rod bearings are designed for engines with crankshaft journals that meet original factory dimensions and tolerances. These bearings restore a smooth, low-friction surface between the connecting rod and crankshaft, ensuring proper oil film formation and minimizing wear under heavy loads.

Commonly used in QSB 4.5 engines that have not undergone crankshaft grinding, standard bearings are the go-to choice during routine overhauls or preventative maintenance. Non-fractured rods in earlier Cummins B Series and QSB engines use a two-piece bearing shell, with upper and lower halves installed into the rod and cap.

Typical Applications:

• Mid-life overhauls for commercial fishing vessels

• Preventative maintenance on harbor tugs and push boats

• Agricultural equipment with extended operating hours

Oversize Bearings for Non-Fractured Rods (0.25 mm and 0.50 mm)

Oversize bearings are used when crankshaft journals have been reground to restore roundness and eliminate scoring or pitting. The oversize designation refers to the additional bearing material needed to match the reduced crankshaft diameter.

• 0.25 mm Oversize Bearings: Ideal for journals with minimal wear that require only light grinding.

• 0.50 mm Oversize Bearings: Suitable for crankshafts that need a deeper grind to remove heavy scoring or heat damage.

Using the correct oversize bearing ensures optimal oil clearance, reducing the risk of bearing failure and extending engine life.

Standard and Oversize Bearings for Fracture-Split Rods

Later-model Cummins QSB 4.5 engines often feature fracture-split connecting rods. This manufacturing technique creates a perfectly matched mating surface between the rod and cap by intentionally breaking the cap from the rod during production. While stronger and more precise, these rods require bearings specifically designed for the fracture-split geometry.

Available Sizes:

• Standard

• 0.25 mm Oversize

• 0.50 mm Oversize

Fracture-split bearings provide the same benefits as their non-fractured counterparts but are manufactured to match the unique shape of the rod bore.

Cummins QSB 4.5 Connecting Rod Bushing

The connecting rod bushing supports the piston pin, allowing the piston to pivot smoothly as the rod moves through its stroke. Over time, bushings can wear, leading to increased clearance, knocking noises, and uneven loading on the piston and crankshaft.

For the QSB 4.5 engine, bushings are made from high-strength bronze or similar alloys, ensuring resistance to galling and scoring. Replacing the bushing during an overhaul is critical for maintaining proper piston alignment and preventing side loading that could damage the cylinder walls.

Connecting Rod Cap Bolts

Early-Style Bolts for Non-Fractured Rods

These bolts secure the connecting rod cap to the rod body in engines equipped with traditional non-fractured rods. They are designed to handle extreme tensile loads without stretching, ensuring the rod and cap remain perfectly aligned under combustion pressure.

Bolts for Fracture-Split Connecting Rods

Fracture-split rods use specialized bolts that are engineered to match the precise geometry of the fractured mating surfaces. Using the correct bolt type is essential—mixing bolt styles between rod designs can cause misalignment, bearing failure, and catastrophic engine damage.

Importance of Choosing the Right Connecting Rod Components

Servicing the connecting rod assembly on your Cummins QSB 4.5 engine isn’t just a matter of replacing worn parts—it’s about ensuring proper clearances, material compatibility, and installation torque. A mismatch in bearing size, bolt type, or bushing fit can lead to premature wear or engine failure.

Best Practices for Connecting Rod Service:

1. Measure crankshaft journals with a micrometer before selecting bearing size.

2. Always replace connecting rod bolts when servicing rods to ensure proper clamping force.

3. Press-fit bushings using precision equipment to avoid distortion.

4. Lubricate all bearing surfaces with assembly lube during installation.

5. Torque bolts to Cummins factory specifications using a calibrated torque wrench.

Marine & Industrial Applications for the QSB 4.5 Connecting Rod Assembly

The Cummins QSB 4.5 engine is widely used in:

• Commercial fishing vessels

• Passenger ferries

• Tugboats and push boats

• Agricultural harvesters and irrigation pumps

• Industrial generators and construction equipment

In all of these applications, the connecting rod assembly is subjected to continuous high loads and must operate flawlessly for thousands of hours between overhauls. Diesel Pro Power supplies OEM-spec parts to ensure your engine’s internal components meet or exceed original performance standards.