Replacing the Engine Block on a Caterpillar 920 Wheel Loader with a 3304 Diesel: Compatibility, Identification, and Practical Advice

[MikePhua]

Introduction: When a Block Fails, the Loader Waits
The Caterpillar 920 wheel loader, equipped with the venerable 3304 diesel engine, has earned its reputation for reliability and straightforward mechanics. But when the engine block itself becomes compromised—whether due to cracking, internal damage, or catastrophic failure—finding a replacement becomes a nuanced challenge. This article explores the process of sourcing a compatible block, decoding serial and arrangement numbers, and ensuring a successful rebuild using existing components.
Understanding the 3304 Engine Platform
The CAT 3304 is a four-cylinder, direct-injection diesel engine used across a wide range of Caterpillar equipment, including loaders, graders, and generators. Known for its robust cast iron block and mechanical simplicity, the 3304 comes in several configurations:

• Naturally aspirated or turbocharged
  
• Industrial, marine, and generator variants
  
• Multiple arrangement numbers based on application-specific components
  

Key specifications:

• Displacement: 7.0 liters (427 cubic inches)
  
• Bore x Stroke: 4.75" x 6.00"
  
• Power output: 85–125 HP depending on configuration
  
• Compression ratio: ~16:1
  
• Dry weight: ~1,100 lbs (block only)
  

Terminology Clarification
- Engine Serial Number (ESN): Unique identifier for each engine, typically stamped on the block
- Arrangement Number: A Caterpillar-specific code that defines the combination of components used in a particular engine build
- Short Block: An engine block with crankshaft, pistons, and connecting rods, but no cylinder head or accessories
- Long Block: A more complete assembly including the cylinder head and valve train
- Core Matching: Ensuring that a replacement block matches the original engine’s configuration for bolt patterns, oil passages, and mounting points
Compatibility Challenges: Matching Blocks by Serial and Arrangement
In one real-world case, a user sought to replace a damaged 3304 block with a used unit. The original engine had serial number 48V47511 and arrangement number 6A7360. The candidate replacement had serial number 48V19586 and arrangement number 6A7362. While the serial number prefix (48V) confirmed both engines were from the same family, the differing arrangement numbers raised concerns.
What matters most:

• The casting number on the block itself (often more reliable than arrangement number)
  
• Whether the oil passages, mounting bosses, and accessory ports match
  
• If the replacement block was used in a similar application (e.g., wheel loader vs. generator)
  
• Whether the crankshaft, camshaft, and timing gear compatibility is preserved
  

Caterpillar’s arrangement numbers often differ by minor component changes—such as fuel pump type, oil pan shape, or flywheel housing. In many cases, a block with a different arrangement number can be used if the core casting is identical and the user plans to reuse all original components.
Recommended Steps for Block Replacement
To ensure a smooth swap:

• Inspect the casting number on both blocks—this is usually cast into the side of the block and is more definitive than arrangement number
  
• Compare oil gallery plugs, coolant ports, and mounting bosses
  
• Confirm crankshaft journal dimensions and bearing compatibility
  
• Reuse original cylinder head, fuel system, and accessories if possible
  
• Replace all gaskets, seals, and wear components during reassembly
  
• Flush oil passages and inspect for cracks using dye penetrant or magnetic particle testing
  

If uncertain, consult a Caterpillar dealer or engine rebuilder with access to technical bulletins and cross-reference databases.
Field Anecdote: A Loader Saved by a Generator Block
In a Swedish logging operation, a 920 loader suffered a cracked block due to a winter freeze. The operator sourced a 3304 block from a decommissioned generator set. Though the arrangement number differed, the core casting matched. After swapping the oil pan and flywheel housing, the engine was rebuilt using all original loader components. The machine returned to service within a week, saving thousands in downtime.
Alternative Sources for Replacement Blocks
Options include:

• Salvage yards specializing in Caterpillar equipment
  
• Generator sets with low-hour 3304 engines
  
• Marine engine rebuilders (verify corrosion and saltwater exposure)
  
• Remanufactured short blocks from certified rebuilders
  
• Online marketplaces with verified casting numbers and photos
  

Always verify:

• Block is free of cracks, corrosion, and excessive wear
  
• Cylinder bores are within spec or ready for sleeving
  
• Main bearing saddles are undamaged
  
• Oil and coolant passages are clean and unobstructed
  

Preventive Measures to Avoid Future Block Damage
To extend engine life:

• Use proper coolant mix and maintain freeze protection
  
• Monitor oil pressure and temperature regularly
  
• Avoid overloading or overheating the engine
  
• Replace worn engine mounts to reduce vibration stress
  
• Drain coolant during long-term storage in freezing climates
  

Conclusion: Matching Metal with Confidence
Replacing a 3304 engine block in a Caterpillar 920 loader is a task that blends mechanical skill with investigative diligence. While serial and arrangement numbers provide clues, the true compatibility lies in the casting and configuration. With careful inspection, reuse of original components, and attention to detail, a replacement block can restore the loader to full working order—proving once again that even old iron can be reborn with the right hands and the right match.