Rebuilding the Belt System on the Caterpillar D4H Dozer with the 3204 Engine

[MikePhua]

The D4H and Its Mechanical Legacy
The Caterpillar D4H is a mid-sized crawler dozer introduced in the 1980s, designed for grading, land clearing, and light earthmoving. It was powered by the Cat 3204 engine—a naturally aspirated four-cylinder diesel known for its simplicity and reliability. With an operating weight of around 10 tons and a drawbar horsepower rating near 90 hp, the D4H became a staple in forestry, roadwork, and utility fleets across North America and beyond.
The 3204 engine was widely used in multiple Caterpillar platforms, including loaders, graders, and agricultural tractors. Its belt-driven accessory system—comprising the fan, alternator, and water pump—was designed for ease of service but required precise belt sizing and alignment to maintain cooling and electrical performance.
Understanding the Belt Layout
The D4H’s front accessory drive system uses a multi-belt configuration:

• A matched set of two belts drives the fan and alternator
  
• A separate single belt powers the water pump
  

Terminology annotation:

• Matched Belt Set: Two belts of identical length and tension used together to distribute load evenly across pulleys.
  
• Fan Pulley: A driven wheel mounted to the engine’s fan hub, responsible for circulating air through the radiator.
  
• Water Pump Pulley: A wheel connected to the impeller shaft of the water pump, circulating coolant through the engine block and radiator.
  

The fan and alternator belt set is identified by Caterpillar part number 4W-8729. These belts are designed to operate in tandem and must be replaced together to avoid uneven wear or slippage. The water pump belt is part number 8N-3113, a single V-belt that connects the crankshaft pulley to the pump.
Installation Tips and Belt Routing
When installing or replacing belts on the D4H:

• Always loosen the alternator and water pump mounting bolts to relieve tension before removal
  
• Route the fan and alternator belts first, ensuring they sit evenly in the pulley grooves
  
• Install the water pump belt last, verifying that it does not interfere with the fan belt path
  
• Use a belt tension gauge to confirm proper deflection—typically 1/2 inch of play under moderate thumb pressure
  

Recommendations:

• Replace belts every 1,000 operating hours or annually, whichever comes first
  
• Inspect pulleys for rust, scoring, or misalignment before installation
  
• Avoid mixing belt brands or types—matched sets must be identical in construction and length
  
• After installation, run the engine at idle for 10 minutes and recheck tension
  

Common Issues and Field Repairs
Operators have reported several recurring issues with the D4H belt system:

• Belt squeal during cold starts, often due to under-tensioned alternator belts
  
• Premature belt wear caused by misaligned pulleys or worn bearings
  
• Overheating traced to a slipping water pump belt, especially under heavy load
  

In one case, a forestry crew in British Columbia experienced repeated belt failures during winter operations. After inspecting the fan hub, they discovered a bent pulley flange that caused uneven belt wear. Replacing the pulley and switching to OEM belts resolved the issue.
Sourcing and Compatibility
While aftermarket belts are available, Caterpillar’s OEM parts offer superior fit and longevity. The 4W-8729 matched set is manufactured to precise tolerances, ensuring synchronized operation of the fan and alternator. The 8N-3113 water pump belt is reinforced for high-temperature environments and resists stretching under load.
If OEM belts are unavailable, use the following specifications:

• Fan/Alternator belts: Matched V-belts, 39.5–40 inches in length, 1/2 inch width
  
• Water pump belt: Single V-belt, approximately 42 inches in length, 1/2 inch width
  

Always verify belt dimensions against pulley spacing and tensioner range before installation.
Preventative Maintenance and Long-Term Reliability
To extend the life of the D4H’s belt system:

• Clean pulleys and belt surfaces during every oil change
  
• Check belt tension monthly, especially in high-vibration environments
  
• Replace tensioner bushings and mounting bolts every 2,000 hours
  
• Keep a spare matched belt set and water pump belt on board for field emergencies
  

In dusty or abrasive environments, consider installing a belt guard or shroud to reduce debris accumulation. Belt failure in remote areas can lead to overheating and electrical loss, so proactive maintenance is essential.
Conclusion
The Caterpillar D4H’s belt-driven accessory system is a straightforward but critical component of its cooling and charging architecture. With proper belt selection, installation, and tensioning, operators can ensure reliable performance from the 3204 engine—even in demanding conditions. Whether clearing land or grading roads, a well-maintained belt system keeps the D4H running cool, charged, and ready for work.