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The Clark 668 and the Rise of Purpose-Built Logging Machines
Clark Equipment Company, founded in 1916 in Michigan, played a pivotal role in the mechanization of forestry. By the 1960s, Clark had become a leading manufacturer of skidders—machines designed specifically for dragging logs from the forest to the landing. The 668 model, introduced during the height of North American logging expansion, was a mid-size articulated four-wheel-drive skidder built for rugged terrain and heavy loads.
The 668 was powered by a Detroit Diesel 4-53 two-stroke engine, delivering around 140 horsepower. Its mechanical transmission, planetary axles, and cable winch system made it a favorite among loggers working in steep, muddy, or snow-covered environments. With a reputation for brute strength and mechanical simplicity, the 668 became a staple in logging operations from Oregon to Ontario.
Terminology Notes
The Clark 668 was built for abuse. Its heavy-duty frame, open cab design, and straightforward hydraulics made it easy to repair in the field. Key features included:
A logger in British Columbia recalled using a 668 in the 1980s to haul cedar in deep snow. The machine never failed to start, even in -20°C, but required daily greasing and frequent cable adjustments. He described it as “a beast with no manners—but it got the job done.”
Common Issues and Restoration Challenges
As surviving units age, several mechanical problems tend to surface:
Preservation and Collector Interest
Vintage skidders like the Clark 668 have gained interest among equipment collectors and forestry museums. Their mechanical purity and historical significance make them ideal restoration candidates. Some owners preserve them for demonstration logging events, while others use them on private woodlots where speed is less important than reliability.
A retired logger in Maine restored his 668 over two winters, repainting it in Clark yellow and rebuilding the winch. He now uses it to pull firewood logs and occasionally displays it at county fairs. “It’s loud, it’s rough, and it’s honest,” he said. “You feel every bolt working.”
Recommendations for Owners and Mechanics
Conclusion
The Clark 668 skidder is more than a machine—it’s a symbol of an era when logging was raw, mechanical, and unforgiving. Its survival into the 21st century speaks to its durability and the skill of those who maintain it. Whether pulling timber in the backwoods or sitting proudly in a restoration yard, the 668 remains a testament to industrial grit and forestry heritage. In the world of logging, some machines fade—but legends like the 668 endure.
Clark Equipment Company, founded in 1916 in Michigan, played a pivotal role in the mechanization of forestry. By the 1960s, Clark had become a leading manufacturer of skidders—machines designed specifically for dragging logs from the forest to the landing. The 668 model, introduced during the height of North American logging expansion, was a mid-size articulated four-wheel-drive skidder built for rugged terrain and heavy loads.
The 668 was powered by a Detroit Diesel 4-53 two-stroke engine, delivering around 140 horsepower. Its mechanical transmission, planetary axles, and cable winch system made it a favorite among loggers working in steep, muddy, or snow-covered environments. With a reputation for brute strength and mechanical simplicity, the 668 became a staple in logging operations from Oregon to Ontario.
Terminology Notes
- Skidder: A forestry machine used to drag felled trees from the cutting site to a central location for processing or transport.
- Articulated Frame: A chassis design that allows the front and rear halves of the machine to pivot, improving maneuverability in tight woods.
- Winch Drum: A rotating spool used to wind cable for pulling logs.
The Clark 668 was built for abuse. Its heavy-duty frame, open cab design, and straightforward hydraulics made it easy to repair in the field. Key features included:
- Detroit Diesel 4-53 engine with mechanical governor
- 4-speed Clark transmission with torque converter
- Rockwell planetary axles for high torque delivery
- Gear-driven winch with mechanical clutch
- Manual steering with hydraulic assist on later models
A logger in British Columbia recalled using a 668 in the 1980s to haul cedar in deep snow. The machine never failed to start, even in -20°C, but required daily greasing and frequent cable adjustments. He described it as “a beast with no manners—but it got the job done.”
Common Issues and Restoration Challenges
As surviving units age, several mechanical problems tend to surface:
- Engine blow-by due to worn piston rings
- Transmission slipping or delayed engagement
- Hydraulic leaks from aged hoses and fittings
- Winch clutch wear causing cable slippage
- Electrical system corrosion in exposed wiring
- Rebuilding the Detroit Diesel with new liners, rings, and injectors
- Replacing transmission seals and torque converter bearings
- Installing modern hydraulic hoses with crimped fittings
- Retrofitting LED lighting and weatherproof switches
- Replacing winch cable and drum bushings
Preservation and Collector Interest
Vintage skidders like the Clark 668 have gained interest among equipment collectors and forestry museums. Their mechanical purity and historical significance make them ideal restoration candidates. Some owners preserve them for demonstration logging events, while others use them on private woodlots where speed is less important than reliability.
A retired logger in Maine restored his 668 over two winters, repainting it in Clark yellow and rebuilding the winch. He now uses it to pull firewood logs and occasionally displays it at county fairs. “It’s loud, it’s rough, and it’s honest,” he said. “You feel every bolt working.”
Recommendations for Owners and Mechanics
- Use high-zinc oil to protect flat tappet camshafts in the Detroit Diesel
- Grease all pivot points weekly, especially articulation joints
- Inspect winch cable for fraying and replace annually
- Flush hydraulic fluid every 500 hours and replace filters
- Keep spare belts, hoses, and injector tips on hand for field repairs
Conclusion
The Clark 668 skidder is more than a machine—it’s a symbol of an era when logging was raw, mechanical, and unforgiving. Its survival into the 21st century speaks to its durability and the skill of those who maintain it. Whether pulling timber in the backwoods or sitting proudly in a restoration yard, the 668 remains a testament to industrial grit and forestry heritage. In the world of logging, some machines fade—but legends like the 668 endure.
