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The Challenge of Field Repacking Large Cylinders
Repacking a large hydraulic cylinder—especially one mounted horizontally on a track loader or dozer—is a physically demanding and technically delicate task. Machines like the Allis-Chalmers HD7-G, built during the mid-20th century, feature lift rams with diameters exceeding 6 inches and piston assemblies weighing over 150 lbs. These components were designed for brute strength, not ease of service. When seals begin to leak or packing wears out, field repairs become a test of ingenuity, patience, and mechanical skill.
Terminology:
- Lift Ram: A hydraulic cylinder responsible for raising and lowering the loader arms or blade. - Packing: A set of seals and rings inside the cylinder that prevent hydraulic fluid from leaking past the piston or rod.
Weight Management and Alignment Techniques
One of the most difficult parts of repacking a large cylinder is reinserting the piston and rod into the barrel without damaging the new seals. With the cylinder still mounted to the machine and oriented horizontally, gravity works against the technician. The rod must be suspended, aligned precisely, and pushed into a recessed bore without tearing the packing.
A practical solution involves using two cable come-alongs—one on each side of the rod eye—anchored near the barrel. With the rod suspended from a hoist or pipe passed through the pin eye, the operator can slowly “walk” the piston into the bore. This method allows fine control and reduces the risk of misalignment.
Terminology:
- Come-Along: A hand-operated winch with a ratcheting mechanism used to pull or lift heavy objects. - Rod Eye: The loop or clevis at the end of the cylinder rod used for mounting.
Seal Protection and Insertion Tools
Even with perfect alignment, the piston seals are vulnerable during insertion. Forcing the piston into the bore without compressing the seals properly can result in torn packing—wasting time and money. A common workaround is to use a ring compressor, typically found in automotive engine work. These adjustable band-style tools compress the seal evenly around the piston, allowing it to slide into the cylinder without damage.
This technique has proven effective not only for hydraulic cylinders but also for installing Caterpillar-style duo-cone seals, which require uniform compression to seat properly.
Terminology:
- Ring Compressor: A tool used to compress piston rings or seals for insertion into a bore. - Duo-Cone Seal: A heavy-duty seal used in final drives and track systems, consisting of two conical sealing surfaces.
Choosing the Right Packing Materials
Seal quality plays a major role in the longevity of a repacked cylinder. In one case, genuine Agco-manufactured packing was used instead of generic aftermarket kits. These OEM seals are formulated for the specific pressures and fluid compatibility of the original machine. While they may cost more, they reduce the likelihood of premature leaks and improve the feel of the hydraulic system.
Recommendations for seal selection:
- Wiper Seal: A seal that scrapes dirt and debris off the rod as it retracts into the cylinder. - Operating Pressure: The maximum hydraulic pressure the system is designed to handle, often exceeding 2,500 psi in heavy equipment.
Rod Damage and Long-Term Maintenance
Large hydraulic rods are expensive to replace. A 2.5-inch diameter rod with minor scratches may still function, but over time it will cause seal wear and fluid weeping. Some operators choose to polish the rod and monitor performance, repacking every few years rather than investing in a $1,500 replacement.
Preventive measures include:
Terminology:
- Rod Boot: A flexible cover that protects the rod from dust and debris. - Side-Loading: A condition where the cylinder is subjected to lateral forces, increasing wear on seals and bearings.
Historical Context and Equipment Legacy
The Allis-Chalmers HD7-G was part of a lineage of track loaders and dozers produced from the 1940s through the 1970s. Allis-Chalmers, founded in Milwaukee in 1901, was a major player in agricultural and industrial machinery. The HD series was known for its rugged construction and straightforward mechanical systems, making it popular among contractors and municipalities.
Though the company exited the construction equipment market in the 1980s, many of its machines remain in service today. Their simplicity and overbuilt components make them ideal candidates for restoration and field repair. Repacking a cylinder on one of these machines is not just maintenance—it’s a continuation of a legacy.
Terminology:
- Track Loader: A crawler-type machine with a front-mounted bucket, used for loading and grading. - Legacy Equipment: Older machinery still in use due to durability and ease of repair.
Conclusion
Repacking large hydraulic cylinders in the field is a blend of brute strength, mechanical finesse, and creative problem-solving. Whether you're working under the summer sun or in a remote quarry, the right tools and techniques can turn a frustrating job into a successful repair. From cable come-alongs to ring compressors, each method reflects the ingenuity of operators who keep aging iron alive. In the world of heavy equipment, experience and adaptation often matter more than factory instructions.
Repacking a large hydraulic cylinder—especially one mounted horizontally on a track loader or dozer—is a physically demanding and technically delicate task. Machines like the Allis-Chalmers HD7-G, built during the mid-20th century, feature lift rams with diameters exceeding 6 inches and piston assemblies weighing over 150 lbs. These components were designed for brute strength, not ease of service. When seals begin to leak or packing wears out, field repairs become a test of ingenuity, patience, and mechanical skill.
Terminology:
- Lift Ram: A hydraulic cylinder responsible for raising and lowering the loader arms or blade. - Packing: A set of seals and rings inside the cylinder that prevent hydraulic fluid from leaking past the piston or rod.
Weight Management and Alignment Techniques
One of the most difficult parts of repacking a large cylinder is reinserting the piston and rod into the barrel without damaging the new seals. With the cylinder still mounted to the machine and oriented horizontally, gravity works against the technician. The rod must be suspended, aligned precisely, and pushed into a recessed bore without tearing the packing.
A practical solution involves using two cable come-alongs—one on each side of the rod eye—anchored near the barrel. With the rod suspended from a hoist or pipe passed through the pin eye, the operator can slowly “walk” the piston into the bore. This method allows fine control and reduces the risk of misalignment.
Terminology:
- Come-Along: A hand-operated winch with a ratcheting mechanism used to pull or lift heavy objects. - Rod Eye: The loop or clevis at the end of the cylinder rod used for mounting.
Seal Protection and Insertion Tools
Even with perfect alignment, the piston seals are vulnerable during insertion. Forcing the piston into the bore without compressing the seals properly can result in torn packing—wasting time and money. A common workaround is to use a ring compressor, typically found in automotive engine work. These adjustable band-style tools compress the seal evenly around the piston, allowing it to slide into the cylinder without damage.
This technique has proven effective not only for hydraulic cylinders but also for installing Caterpillar-style duo-cone seals, which require uniform compression to seat properly.
Terminology:
- Ring Compressor: A tool used to compress piston rings or seals for insertion into a bore. - Duo-Cone Seal: A heavy-duty seal used in final drives and track systems, consisting of two conical sealing surfaces.
Choosing the Right Packing Materials
Seal quality plays a major role in the longevity of a repacked cylinder. In one case, genuine Agco-manufactured packing was used instead of generic aftermarket kits. These OEM seals are formulated for the specific pressures and fluid compatibility of the original machine. While they may cost more, they reduce the likelihood of premature leaks and improve the feel of the hydraulic system.
Recommendations for seal selection:
- Use OEM or high-quality aftermarket kits rated for the machine’s operating pressure
- Avoid forcing seals into place—use lubrication and compression tools
- Inspect the rod for scratches or pitting before installation
- Replace worn wipers and dust seals to prevent contamination
- Wiper Seal: A seal that scrapes dirt and debris off the rod as it retracts into the cylinder. - Operating Pressure: The maximum hydraulic pressure the system is designed to handle, often exceeding 2,500 psi in heavy equipment.
Rod Damage and Long-Term Maintenance
Large hydraulic rods are expensive to replace. A 2.5-inch diameter rod with minor scratches may still function, but over time it will cause seal wear and fluid weeping. Some operators choose to polish the rod and monitor performance, repacking every few years rather than investing in a $1,500 replacement.
Preventive measures include:
- Applying rust inhibitors during storage
- Using rod boots or guards in abrasive environments
- Avoiding side-loading or misalignment during operation
- Keeping the machine clean to reduce grit intrusion
Terminology:
- Rod Boot: A flexible cover that protects the rod from dust and debris. - Side-Loading: A condition where the cylinder is subjected to lateral forces, increasing wear on seals and bearings.
Historical Context and Equipment Legacy
The Allis-Chalmers HD7-G was part of a lineage of track loaders and dozers produced from the 1940s through the 1970s. Allis-Chalmers, founded in Milwaukee in 1901, was a major player in agricultural and industrial machinery. The HD series was known for its rugged construction and straightforward mechanical systems, making it popular among contractors and municipalities.
Though the company exited the construction equipment market in the 1980s, many of its machines remain in service today. Their simplicity and overbuilt components make them ideal candidates for restoration and field repair. Repacking a cylinder on one of these machines is not just maintenance—it’s a continuation of a legacy.
Terminology:
- Track Loader: A crawler-type machine with a front-mounted bucket, used for loading and grading. - Legacy Equipment: Older machinery still in use due to durability and ease of repair.
Conclusion
Repacking large hydraulic cylinders in the field is a blend of brute strength, mechanical finesse, and creative problem-solving. Whether you're working under the summer sun or in a remote quarry, the right tools and techniques can turn a frustrating job into a successful repair. From cable come-alongs to ring compressors, each method reflects the ingenuity of operators who keep aging iron alive. In the world of heavy equipment, experience and adaptation often matter more than factory instructions.
