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Overview of the Liebherr 611
The Liebherr 611 is a tracked crawler loader that gained popularity in the 1970s and 1980s due to its sturdy construction, smooth hydrostatic drive, and the reliable Mercedes-Benz OM352 engine. As a compact and powerful machine, it was often found on construction sites across Europe and North America, used for grading, loading, and land clearing. Today, the 611 continues to serve in smaller operations and on private lands, making knowledge of its engine and drivetrain still relevant.
The Heart of the Machine: Mercedes-Benz OM352 Engine
The OM352 is a 5.7-liter inline-six, naturally aspirated diesel engine, known for its durability and ease of maintenance. Developed in the early 1960s, it was used across multiple platforms: trucks, tractors, military vehicles, and construction machinery. In the 611, this engine delivers about 100 to 110 horsepower depending on tuning and application.
Key features of the OM352 include:
While robust, the OM352 is not without its quirks. A few areas require close attention, especially as these engines age.
The Liebherr 611 features a hydrostatic transmission that is both smooth and strong but depends heavily on clean oil and proper pressure. One recurring problem among users is low power output traced not to the engine but to a failing or misconfigured hydraulic pump.
Another frequent issue is starter motor failure. The OEM Bosch starter draws high amperage, and any weakness in the battery or cable can lead to poor cranking. Some users opt for a gear reduction starter, which spins faster with less amperage—an upgrade especially beneficial in cold climates.
Electrical wiring on the 611 is simple but not always well-documented. Owners sometimes find wire colors inconsistent, suggesting in-factory changes or previous repairs. Creating your own wiring diagram as you trace systems is often the most reliable way to resolve electrical gremlins.
Cold Starting: A Ritual of Its Own
Starting the OM352 in cold weather can be tricky. While equipped with glow plugs, older machines might also have an ether injection system or even a manual decompression lever. Some tips for cold starts include:
Parts Availability and Substitutions
Many parts for the OM352 remain available through Mercedes industrial suppliers and heavy truck dealers. However, certain parts like specific injector lines, starter motors, or older alternators may require creative sourcing.
Some replacement practices include:
Stories from the Field
One owner recounted how his 611 outlasted two newer loaders on a rural job site. Despite its age, the machine ran daily for six months with nothing more than a new fuel filter and fresh batteries. He claimed, only half-jokingly, that the OM352 would run on “diesel, kerosene, or bad intentions.”
Another operator in Montana kept a 611 going for over a decade, using it for trail clearing and fire line maintenance. When the injection pump began leaking, he rebuilt it on his kitchen table with nothing more than a repair manual and a set of seals bought off a local diesel shop.
Conclusion: A Machine That Earns Respect
The Liebherr 611, paired with the Mercedes OM352, is a testament to durable design. With proper care, these machines continue to serve long after their expected service life. Their simplicity is both a blessing and a challenge—it rewards hands-on knowledge and punishes neglect. For those willing to learn its ways, the 611 is more than a loader; it’s a reliable companion built in an era when overengineering was a virtue, not a flaw.
The Liebherr 611 is a tracked crawler loader that gained popularity in the 1970s and 1980s due to its sturdy construction, smooth hydrostatic drive, and the reliable Mercedes-Benz OM352 engine. As a compact and powerful machine, it was often found on construction sites across Europe and North America, used for grading, loading, and land clearing. Today, the 611 continues to serve in smaller operations and on private lands, making knowledge of its engine and drivetrain still relevant.
The Heart of the Machine: Mercedes-Benz OM352 Engine
The OM352 is a 5.7-liter inline-six, naturally aspirated diesel engine, known for its durability and ease of maintenance. Developed in the early 1960s, it was used across multiple platforms: trucks, tractors, military vehicles, and construction machinery. In the 611, this engine delivers about 100 to 110 horsepower depending on tuning and application.
Key features of the OM352 include:
- Inline-six cylinder layout: Provides good balance and smooth operation.
- Direct injection: Fuel is injected directly into the combustion chamber, improving efficiency and power.
- Mechanical fuel injection pump: Typically a Bosch inline pump, known for reliability and serviceability.
- Cast iron block and head: Extremely robust and tolerant of abuse and poor maintenance.
- Wet replaceable cylinder liners: Allow for easy rebuilding without machining the block.
- Naturally aspirated (in most 611s): No turbocharger, which simplifies upkeep.
While robust, the OM352 is not without its quirks. A few areas require close attention, especially as these engines age.
- Fuel system bleeding: After filter replacement or running out of fuel, the injection system must be properly bled. This involves cracking injector lines and using the hand primer to remove air.
- Valve adjustments: Regular adjustment ensures efficient operation and prevents valve damage.
- Glow plug operation: The OM352 uses pencil-type glow plugs in many configurations. Starting becomes difficult if even one fails.
- Oil pressure monitoring: Older engines may lose oil pressure due to worn bearings. Keeping an eye on pressure, especially at idle, is crucial.
- Cooling system upkeep: Scale and rust buildup can reduce efficiency. Periodic flushing and inspection of the radiator and water pump are recommended.
The Liebherr 611 features a hydrostatic transmission that is both smooth and strong but depends heavily on clean oil and proper pressure. One recurring problem among users is low power output traced not to the engine but to a failing or misconfigured hydraulic pump.
Another frequent issue is starter motor failure. The OEM Bosch starter draws high amperage, and any weakness in the battery or cable can lead to poor cranking. Some users opt for a gear reduction starter, which spins faster with less amperage—an upgrade especially beneficial in cold climates.
Electrical wiring on the 611 is simple but not always well-documented. Owners sometimes find wire colors inconsistent, suggesting in-factory changes or previous repairs. Creating your own wiring diagram as you trace systems is often the most reliable way to resolve electrical gremlins.
Cold Starting: A Ritual of Its Own
Starting the OM352 in cold weather can be tricky. While equipped with glow plugs, older machines might also have an ether injection system or even a manual decompression lever. Some tips for cold starts include:
- Use of block heater: A 110V heater in the coolant circuit dramatically improves cranking success.
- Battery condition: Cold cranking amps are vital—this engine turns slowly when cold.
- Proper glow plug procedure: Holding the glow for 20-30 seconds before attempting start may be required.
- Avoid ether unless necessary: Overuse of starting fluid can damage the engine, especially if glow plugs are active.
Parts Availability and Substitutions
Many parts for the OM352 remain available through Mercedes industrial suppliers and heavy truck dealers. However, certain parts like specific injector lines, starter motors, or older alternators may require creative sourcing.
Some replacement practices include:
- Starter motor: Swapping for a modern gear reduction starter compatible with other Mercedes engines.
- Glow plugs: Using Beru or Bosch replacements from Unimog or MB-Trac sources.
- Filters: Cross-referencing oil and fuel filters with Fram, Mann, or Baldwin catalogues yields many options.
- Fuel lines: Custom-fabricated or reused with proper flaring tools.
Stories from the Field
One owner recounted how his 611 outlasted two newer loaders on a rural job site. Despite its age, the machine ran daily for six months with nothing more than a new fuel filter and fresh batteries. He claimed, only half-jokingly, that the OM352 would run on “diesel, kerosene, or bad intentions.”
Another operator in Montana kept a 611 going for over a decade, using it for trail clearing and fire line maintenance. When the injection pump began leaking, he rebuilt it on his kitchen table with nothing more than a repair manual and a set of seals bought off a local diesel shop.
Conclusion: A Machine That Earns Respect
The Liebherr 611, paired with the Mercedes OM352, is a testament to durable design. With proper care, these machines continue to serve long after their expected service life. Their simplicity is both a blessing and a challenge—it rewards hands-on knowledge and punishes neglect. For those willing to learn its ways, the 611 is more than a loader; it’s a reliable companion built in an era when overengineering was a virtue, not a flaw.
