CAT 259D Engine Rebuild and the Realities of V3307 Overhaul

[MikePhua]

The CAT 259D and Its Compact Powerhouse
The Caterpillar 259D compact track loader is part of CAT’s D-series lineup, designed for high performance in confined spaces. With:

• Rated operating capacity: 2,900 lbs
  
• Net power: 73.2 hp
  
• Engine: CAT 3.3B (Kubota V3307 turbocharged diesel)
  

This machine became a favorite among contractors and landscapers for its vertical lift design, two-speed travel, and ergonomic cab. The engine, though branded by CAT, is a Kubota V3307—a proven four-cylinder platform used across agriculture, construction, and industrial sectors.
Head Gasket Failure and Cylinder Scoring
A common issue with the V3307 is head gasket failure, which can lead to:

• Coolant intrusion into combustion chambers
  
• Overheating and white exhaust smoke
  
• Cylinder wall scoring due to coolant wash or debris
  

In one case, two cylinders showed light scoring. While compression wasn’t drastically affected, long-term reliability was at risk.
Rebuild Options and Oversized Components
Rebuilding the V3307 often involves boring cylinders and installing oversized pistons. Key steps include:

• Measuring cylinder taper and out-of-round
  
• Boring and honing to +0.5 mm or +1.0 mm
  
• Installing matched oversized pistons and rings
  
• Replacing bearings, valve seals, and oil pump
  
• Verifying timing gear backlash and oil clearance
  

This approach is common in agricultural rebuilds, where durability outweighs cost.
Aftermarket Kit Quality and Supplier Reliability
Rebuild kits vary in quality. While some suppliers offer complete kits, experienced mechanics prefer:

• Agkits: Known for consistent tolerances
  
• Reliance Power Parts: Trusted in ag and industrial sectors
  

Critical components to inspect:

• Piston alloy and skirt coating
  
• Ring tension and material
  
• Gasket composition (MLS preferred)
  
• Bearing oil groove design
  
• Valve guide metallurgy
  

One operator rejected a cheaper kit due to poor ring gap consistency and mismatched valve seats.
Engine Identification and Cross-Reference Confusion
The CAT 3.3B and Kubota V3307 are mechanically identical but differ in branding. To avoid confusion:

• Use engine serial number (e.g., FTL0246)
  
• Cross-reference casting numbers
  
• Consult Kubota industrial manuals for specs
  
• Verify turbo model and oil routing
  

Some rebuilders have successfully used Bobcat S650 kits, which share the V3307T engine.
Rebuild Challenges and Field Anecdotes
Compact loaders pose unique challenges:

• Tight engine bays and proprietary fasteners
  
• Dust and oil buildup around turbo and intake
  
• Lack of clear documentation for CAT-branded engines
  

One Alberta operator rebuilt his V3307 in a garage using a homemade stand and borrowed bore gauge. His biggest hurdle? Finding a head gasket with the correct turbo oil return port.
Preventive Measures and Long-Term Reliability
To extend engine life:

• Change oil every 250 hours (15W-40 diesel oil)
  
• Use OEM filters with anti-drainback valves
  
• Pressure test coolant system annually
  
• Replace thermostats and radiator caps every 1,000 hours
  
• Inspect turbo for shaft play and leaks
  

Recommended coolant: CAT ELC or equivalent silicate-free extended-life coolant.
Conclusion
Rebuilding the CAT 259D’s 3.3B engine—essentially a Kubota V3307—is a demanding but rewarding process. With precision machining, quality parts, and careful assembly, the engine can be restored to full performance. Understanding the nuances of part sourcing, engine identification, and rebuild strategy is key. The 259D remains a compact workhorse, and with a fresh engine, it’s ready for another chapter of hard-earned productivity.