Cracked Cylinder Heads on the CAT 980B with the 336 V8 Engine

[MikePhua]

The CAT 980B and Its Industrial Legacy
The Caterpillar 980B wheel loader was introduced in the early 1970s as part of CAT’s heavy equipment expansion into high-capacity loading and material handling. Designed for quarry, mining, and large-scale construction operations, the 980B featured a robust frame, planetary final drives, and a high-lift linkage system. With an operating weight exceeding 50,000 lbs and a bucket capacity of up to 6.5 cubic yards, it became a staple in aggregate yards and bulk material terminals.
Caterpillar Inc., founded in 1925, had by then established itself as a global leader in earthmoving equipment. The 980B was powered by the CAT 336 V8 diesel engine—an overhead camshaft design that marked a departure from CAT’s traditional inline configurations. Though powerful, the 336 V8 had a reputation for being temperamental under extreme thermal and mechanical stress.
Understanding the CAT 336 V8 Overhead Cam Engine
The CAT 336 V8 was a naturally aspirated diesel engine with an overhead camshaft (OHC) layout. This design allowed for improved valve timing and higher RPM potential compared to pushrod engines. It featured:

• Eight cylinders in a 90-degree V configuration
  
• Overhead camshaft driven by gears
  
• Wet sleeve cylinder liners
  
• Direct injection fuel system
  
• Cast iron cylinder heads
  

Despite its engineering ambition, the 336 V8 was known for head cracking issues, especially in high-load applications or when cooling systems were neglected.
Terminology Annotation

• Overhead Camshaft (OHC): A valve train configuration where the camshaft is located above the cylinder head, directly actuating the valves.
  
• Wet Sleeve: A removable cylinder liner that is surrounded by coolant, allowing easier rebuilds and better heat dissipation.
  
• Direct Injection: A fuel delivery method where diesel is injected directly into the combustion chamber, improving efficiency.
  
• Casting Stress: Internal tension within metal components caused during manufacturing, which can lead to cracking under thermal cycling.
  

Cracked Cylinder Heads and Their Causes
Cracked heads on the CAT 336 V8 typically occur between the valve seats or around the injector ports. Contributing factors include:

• Overheating due to clogged radiators or failed thermostats
  
• Uneven torque during head installation
  
• Poor coolant maintenance leading to corrosion
  
• Thermal shock from rapid temperature changes
  

In one documented case, a 980B operating in a limestone quarry experienced repeated head failures after a radiator fan clutch seized, causing chronic overheating. The heads were replaced twice before the root cause was identified.
Inspection and Diagnosis
To confirm cracked heads, technicians should:

• Perform a coolant pressure test to detect leaks
  
• Use dye penetrant or magnetic particle inspection on suspect areas
  
• Remove the heads and inspect for visible fractures
  
• Check for combustion gases in the cooling system
  

If cracks are found, replacement is often more practical than repair. Welding cast iron heads is possible but requires preheating, controlled cooling, and post-weld machining—skills not always available in the field.
Replacement and Compatibility Challenges
Finding replacement heads for the CAT 336 V8 can be difficult due to limited production and discontinued support. Options include:

• Salvage yards specializing in vintage CAT components
  
• Custom casting from engine rebuild shops
  
• Retrofitting with compatible heads from similar CAT engines (requires machining and validation)
  

When replacing heads, always:

• Use new head gaskets and torque to spec in proper sequence
  
• Flush the cooling system thoroughly
  
• Inspect block deck for warping or erosion
  
• Replace head bolts if stretch-type fasteners were used
  

Alternative Powertrain Considerations
Given the age and parts scarcity of the 336 V8, some operators consider repowering the 980B with a more modern engine. Popular choices include:

• CAT 3406 inline-six turbocharged diesel
  
• Cummins N14 or ISX series
  
• Detroit Diesel Series 60
  

Repowering requires:

• Custom engine mounts and bellhousing adapters
  
• Rewiring of gauges and sensors
  
• Matching torque converter or transmission input
  
• Cooling system upgrades
  

A contractor in Alberta successfully retrofitted a 980B with a CAT 3406E, gaining improved fuel economy and easier parts access. The project took three weeks and cost under $20,000, including labor.
Preventive Measures and Maintenance Tips
To avoid head cracking in remaining 336 V8 units:

• Maintain coolant levels and quality with regular flushes
  
• Monitor engine temperature with aftermarket sensors
  
• Avoid rapid shutdowns after heavy load cycles
  
• Use proper torque procedures during head installation
  
• Inspect valve lash and injector seating annually
  

In 2023, a fleet manager in Nevada implemented a thermal monitoring protocol for all legacy CAT engines. Within a year, head-related failures dropped by 60%, and engine uptime improved across the board.
Conclusion
The CAT 980B remains a symbol of industrial strength, but its 336 V8 engine presents unique challenges—especially when cylinder heads begin to crack. Whether choosing to repair, replace, or repower, understanding the engine’s design and limitations is key to keeping these machines productive. In the world of heavy equipment, durability is earned not just through steel, but through smart decisions and timely intervention.