Cummins 4BTA Crankshaft & Bottom End Components Catalog

The Cummins 4BTA 3.9-liter diesel engine has earned a reputation worldwide for durability, simplicity, and long service life in both marine and industrial applications. At the heart of that reliability is its crankshaft—a precision-machined, high-strength steel component that converts the linear force of the pistons into the rotational torque that drives the vessel, generator, pump, or other equipment.

This catalog is dedicated exclusively to the crankshaft and closely related bottom-end components for the Cummins 4BTA, covering new crankshafts, bearing sets, gasket kits, crankshaft seals, vibration dampers, and other critical supporting parts.

With over 40,000 satisfied customers, Diesel Pro Power has become the go-to source for dependable Cummins engine parts that are in stock and ready to ship worldwide.

Engine Overview

The Cummins 4BTA is a turbocharged, aftercooled four-cylinder diesel engine with a displacement of 3.9 liters (239 cubic inches). Its forged steel crankshaft is designed to handle high cylinder pressures and extended duty cycles. In marine configurations, the 4BTA is prized for fuel efficiency and the ability to run reliably under constant load.

The crankshaft assembly plays a crucial role in engine performance, and the components in this section are designed to OEM specifications to maintain factory balance, oil clearances, and smooth operation.

Complete Crankshaft Assemblies for Cummins 4BTA

New Crankshaft Assemblies

A complete new crankshaft for the 4BTA is the foundation for a major bottom-end rebuild or replacement. These assemblies are precision balanced and machined from high-strength steel, with hardened journals to withstand the constant friction and load cycles of marine and industrial service.

Key Features:

• Forged steel construction for maximum strength

• Precision-ground main and rod journals

• Heat-treated surfaces for wear resistance

• Balanced to factory specifications to reduce vibration

• Ready to install with standard bearing sizes

A new crankshaft is the best choice when damage such as scoring, cracks, or excessive wear makes machining impractical. It is also the preferred solution in high-hour rebuilds where long-term reliability is the priority.

Bearing Sets for Cummins 4BTA

The crankshaft relies on a series of main bearings to support it within the block and rod bearings to connect it to the pistons. Maintaining the correct oil clearance between the journals and bearings is vital for longevity.

Standard Size Crankshaft Bearing Sets

Standard bearing sets are used when the crankshaft journals are still within OEM specifications after inspection. These bearings feature precision-machined surfaces and high-strength overlay materials to handle sustained load.

Applications:

• Routine rebuilds where crankshaft wear is minimal

• Engines where oil pressure and bearing clearances remain within spec

Oversize Bearing Sets (0.25 mm and 0.50 mm)

Oversize bearings are designed for crankshafts that have been reground to restore surface finish and roundness. The oversize measurement compensates for the reduced journal diameter after machining.

When to Use Oversize Bearings:

• Journal wear or scoring has been repaired by grinding

• Oil clearances need to be restored to factory spec

• Preventing metal-to-metal contact and premature wear

All bearing sets in this catalog include both upper and lower halves for a complete replacement across the engine.

Gasket Sets Related to Crankshaft Service

Replacing or servicing the crankshaft often requires removal of the oil pan, timing gear cover, and other lower engine components. This means fresh gaskets are essential to prevent oil leaks after reassembly.

Upper Gasket Sets

Upper gasket sets cover components above the crankshaft centerline, including the cylinder head, intake, and exhaust manifold gaskets. While not always replaced during crankshaft service, many rebuilds include these as part of a comprehensive overhaul.

Lower Gasket Sets

Lower gasket sets are directly relevant to crankshaft replacement, containing the oil pan gasket, timing cover gasket, rear main seal housing gasket, and other lower-engine seals. Using a fresh lower gasket set ensures proper sealing after bottom-end work.

Crankshaft Seal Kits for Cummins 4BTA

Crankshaft seals are critical for keeping engine oil in and contaminants out. They are located at both the front and rear of the crankshaft where it exits the engine block.

Front Crankshaft Seal Kits

The front seal prevents oil leakage at the crankshaft nose where it drives the timing gears and accessories. Our kits include not only the high-quality elastomer seal but also sleeves or dust shields where applicable.

Rear Crankshaft Seal Kits

The rear main seal prevents oil loss between the crankshaft and flywheel housing. In marine and industrial engines, a rear seal failure can lead to significant oil loss and downtime. These kits come complete with the seal and sleeve for a precise fit.

Vibration Dampers for Cummins 4BTA

The vibration damper, sometimes called a harmonic balancer, is mounted to the front of the crankshaft to absorb torsional vibrations. Without it, crankshaft twist and flex can lead to fatigue failure over time.

Benefits of a New Vibration Damper:

• Reduced crankshaft stress under heavy load

• Quieter, smoother operation at various RPMs

• Protection of gears, bearings, and timing components from shock loads

Available in multiple diameters to match your specific 4BTA configuration, each damper is manufactured to precise balance specifications.

Expansion Plug Kits for Cummins 4BTA Blocks

While not directly part of the crankshaft assembly, block expansion plugs (also known as freeze plugs) are often replaced during bottom-end rebuilds. These plugs seal the casting holes used during manufacturing and protect against freeze damage in cold environments.

Replacing them during crankshaft service is a cost-effective preventive step, especially for marine engines exposed to saltwater environments.

Importance of Using Quality Cummins 4BTA Crankshaft Parts

The crankshaft operates under extreme forces—combustion pressure, reciprocating mass inertia, and torsional vibration. Poor-quality components or improper installation can lead to:

• Premature bearing wear

• Oil pressure loss

• Crankshaft cracks or journal scoring

• Catastrophic engine failure

By choosing OEM-specification or better components, operators ensure that the crankshaft remains reliable through thousands of hours of service.

Professional Tips for Cummins 4BTA Crankshaft Service

• Always Measure Journals – Use a micrometer to check journal diameters before selecting standard or oversize bearings.

• Check Oil Clearance with Plastigage – This verifies that clearances are within the 0.0015"–0.0030" range typical for the 4BTA.

• Replace Seals and Gaskets – Any crankshaft service should include fresh seals to prevent future oil leaks.

• Inspect Vibration Damper – Replace if rubber isolator shows cracks, bulges, or separation.

• Balance the Assembly – If the crankshaft, flywheel, or damper is replaced, ensure the rotating assembly is balanced to prevent vibration.