09-25-2025, 11:27 AM
The D4H Series II and Its Engine Evolution
The Caterpillar D4H Series II dozer was introduced in the late 1980s as part of CAT’s push to modernize its mid-size track-type tractors. Built for grading, site prep, and forestry work, the D4H Series II featured an elevated sprocket design, improved operator ergonomics, and a hydrostatic transmission that allowed seamless directional changes. At its core was the CAT 3204 engine—a naturally aspirated four-cylinder diesel producing around 90 horsepower.
The 3204 was known for its simplicity and reliability, but some operators sought more torque and durability, especially in demanding applications. This led to interest in retrofitting the larger CAT 3304 engine, a turbocharged inline four-cylinder with a longer stroke and higher output, commonly found in larger machines like the 955L track loader and early D5 models.
Comparing the 3204 and 3304 Engines
While both engines share similar architecture, they differ in key dimensions and performance characteristics:
Challenges in the Engine Swap
Retrofitting a 3304 into a D4H Series II involves several mechanical and logistical hurdles:
Recommended Steps and Precautions
To ensure a successful swap:
Performance Gains and Operational Impact
Once installed, the 3304 delivers:
Field Anecdote and Practical Insight
In Shanghai, a contractor retrofitted a 3304 into a D4H used for landfill compaction. The original 3204 struggled with wet clay and trash piles, often bogging down mid-pass. After the swap, the machine handled the terrain with ease, and cycle times dropped by 20%. The only drawback was increased fuel cost, which was offset by faster job completion.
Conclusion
Swapping a CAT 3204 for a 3304 in the D4H Series II dozer is a bold move that can yield substantial performance gains—but it demands careful planning, fabrication, and system upgrades. For operators working in high-torque environments or seeking extended engine life, the 3304 offers a proven solution. With the right tools and mechanical insight, this retrofit transforms the D4H into a more capable and resilient machine.
The Caterpillar D4H Series II dozer was introduced in the late 1980s as part of CAT’s push to modernize its mid-size track-type tractors. Built for grading, site prep, and forestry work, the D4H Series II featured an elevated sprocket design, improved operator ergonomics, and a hydrostatic transmission that allowed seamless directional changes. At its core was the CAT 3204 engine—a naturally aspirated four-cylinder diesel producing around 90 horsepower.
The 3204 was known for its simplicity and reliability, but some operators sought more torque and durability, especially in demanding applications. This led to interest in retrofitting the larger CAT 3304 engine, a turbocharged inline four-cylinder with a longer stroke and higher output, commonly found in larger machines like the 955L track loader and early D5 models.
Comparing the 3204 and 3304 Engines
While both engines share similar architecture, they differ in key dimensions and performance characteristics:
- Displacement: 3204 = 4.2L, 3304 = 5.4L
- Bore and stroke: 3204 = 105 x 127 mm, 3304 = 114 x 152 mm
- Horsepower: 3204 = ~90 hp, 3304 = ~125–140 hp (depending on turbo and governor)
- Weight: 3304 is approximately 200 lbs heavier
- Mounting: Bellhousing and motor mounts differ slightly
- Cooling: 3304 requires larger radiator and fan shroud clearance
- Fuel system: 3304 uses a different injection pump and governor linkage
Challenges in the Engine Swap
Retrofitting a 3304 into a D4H Series II involves several mechanical and logistical hurdles:
- Bellhousing compatibility: The transmission input shaft and bolt pattern may not align without an adapter plate or custom machining.
- Motor mounts: The frame rails may require modification or new brackets to accommodate the longer block.
- Cooling system: The original radiator may be undersized for the 3304’s heat output, especially if turbocharged. Upgrading to a D5-style radiator is recommended.
- Throttle linkage: The governor arm and cable routing differ between engines and must be reconfigured.
- Exhaust routing: The turbo outlet may interfere with the hood or firewall, requiring custom piping.
- Electrical connections: Temperature and oil pressure sensors may use different threads or voltages.
Recommended Steps and Precautions
To ensure a successful swap:
- Source a complete 3304 engine with flywheel, clutch housing, and accessories
- Measure frame clearance and hood dimensions before removal
- Use OEM torque specs for all mounting bolts and couplings
- Upgrade the cooling system with a high-flow water pump and larger core
- Install new motor mounts with vibration isolators
- Rewire sensor leads and test voltage compatibility
- Flush fuel lines and install a new filter rated for higher flow
Performance Gains and Operational Impact
Once installed, the 3304 delivers:
- Improved torque for pushing and ripping
- Better throttle response under load
- Reduced stalling in soft or uneven terrain
- Higher hydraulic output due to increased RPM stability
Field Anecdote and Practical Insight
In Shanghai, a contractor retrofitted a 3304 into a D4H used for landfill compaction. The original 3204 struggled with wet clay and trash piles, often bogging down mid-pass. After the swap, the machine handled the terrain with ease, and cycle times dropped by 20%. The only drawback was increased fuel cost, which was offset by faster job completion.
Conclusion
Swapping a CAT 3204 for a 3304 in the D4H Series II dozer is a bold move that can yield substantial performance gains—but it demands careful planning, fabrication, and system upgrades. For operators working in high-torque environments or seeking extended engine life, the 3304 offers a proven solution. With the right tools and mechanical insight, this retrofit transforms the D4H into a more capable and resilient machine.
