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Caterpillar’s Giant Earthmovers of the 1960s and 70s
The Caterpillar 660 and 666 scrapers were among the most powerful and visually imposing earthmoving machines of their time. Developed during the late 1960s and early 1970s, these twin-engine scrapers were designed for high-volume hauling in mining, highway construction, and large-scale land development. The 660 featured a tractor-scraper configuration with a single engine, while the 666 was a tandem-powered unit with engines at both the front and rear, delivering exceptional traction and load capacity.
The 666 scraper, in particular, became iconic for its massive size and distinctive sound, powered by two Caterpillar diesel engines—often D343 or D398 V8s—each producing over 400 horsepower. These machines were capable of hauling over 50 cubic yards of material in a single pass, making them ideal for long-haul, high-speed operations.
Tire Sizing and Configuration Variants
One of the most debated aspects of the 660 and 666 scrapers is their tire configuration. Factory specifications typically listed:
Terminology Clarification
Operators who ran 660s and 666s in the Upper Peninsula mines during the 1970s recall their sheer power and reliability. At the Tilden and Empire Mines, these machines moved overburden and ore with relentless efficiency. One mechanic remembered working on emergency generators powered by D398s at the concentrator, noting that nothing matched the deep, rhythmic chug of those engines.
In Alaska, during the pipeline boom of the mid-70s, contractors nicknamed their fleet “Hoover Movers,” referencing the Virginia-based company that ran a mix of aging but dependable equipment. Despite the wear and tear, morale was high, and even breakdowns were met with laughter and camaraderie.
Model Building and Historical Preservation
The scale and presence of the 666 inspired enthusiasts to build detailed steel models. One builder crafted a replica with realistic paint, tire tread, and articulation. While sourcing accurate model tires proved difficult, the effort captured the spirit of the machine. Collectors often debate tire accuracy, but most agree that the essence of the 666 lies in its proportions and mechanical detail.
Recommendations for Restoration and Display
For those restoring or modeling these machines:
The Caterpillar 660 and 666 scrapers represent a golden era of mechanical earthmoving. Their tire configurations, engine setups, and field adaptations reflect both engineering intent and contractor ingenuity. Whether preserved in photos, models, or memories, these machines continue to inspire admiration for their scale, sound, and service in shaping the land.
The Caterpillar 660 and 666 scrapers were among the most powerful and visually imposing earthmoving machines of their time. Developed during the late 1960s and early 1970s, these twin-engine scrapers were designed for high-volume hauling in mining, highway construction, and large-scale land development. The 660 featured a tractor-scraper configuration with a single engine, while the 666 was a tandem-powered unit with engines at both the front and rear, delivering exceptional traction and load capacity.
The 666 scraper, in particular, became iconic for its massive size and distinctive sound, powered by two Caterpillar diesel engines—often D343 or D398 V8s—each producing over 400 horsepower. These machines were capable of hauling over 50 cubic yards of material in a single pass, making them ideal for long-haul, high-speed operations.
Tire Sizing and Configuration Variants
One of the most debated aspects of the 660 and 666 scrapers is their tire configuration. Factory specifications typically listed:
- Front steering axle: 18.00x25 bias ply or radial
- Drive axle: 37.5x39 bias ply or radial
- Scraper axle: 37.5x51 for high-speed haul applications
Terminology Clarification
- Bias Ply Tire: A tire constructed with layers of fabric cords at alternating angles, offering durability but less flexibility than radial designs.
- Radial Tire: A tire with cords running perpendicular to the direction of travel, providing better heat dissipation and longer tread life.
- Scraper Axle: The rear axle supporting the bowl or pan of the scraper, often bearing the heaviest load during hauling.
Operators who ran 660s and 666s in the Upper Peninsula mines during the 1970s recall their sheer power and reliability. At the Tilden and Empire Mines, these machines moved overburden and ore with relentless efficiency. One mechanic remembered working on emergency generators powered by D398s at the concentrator, noting that nothing matched the deep, rhythmic chug of those engines.
In Alaska, during the pipeline boom of the mid-70s, contractors nicknamed their fleet “Hoover Movers,” referencing the Virginia-based company that ran a mix of aging but dependable equipment. Despite the wear and tear, morale was high, and even breakdowns were met with laughter and camaraderie.
Model Building and Historical Preservation
The scale and presence of the 666 inspired enthusiasts to build detailed steel models. One builder crafted a replica with realistic paint, tire tread, and articulation. While sourcing accurate model tires proved difficult, the effort captured the spirit of the machine. Collectors often debate tire accuracy, but most agree that the essence of the 666 lies in its proportions and mechanical detail.
Recommendations for Restoration and Display
For those restoring or modeling these machines:
- Use 37.5x39 tires for general accuracy, unless replicating high-speed haul variants.
- Consider dual tire setups on the drive axle for added realism.
- Reference CPH #3 manuals from 1973 for original specifications.
- Use sound clips of D398 engines to enhance display authenticity.
The Caterpillar 660 and 666 scrapers represent a golden era of mechanical earthmoving. Their tire configurations, engine setups, and field adaptations reflect both engineering intent and contractor ingenuity. Whether preserved in photos, models, or memories, these machines continue to inspire admiration for their scale, sound, and service in shaping the land.
