Reviving a Worn Cat 955L Track Loader

The Caterpillar 955L was introduced in the late 1970s as part of Caterpillar’s evolution in crawler loaders. Built in France and powered by the 3304 pre-combustion chamber diesel engine, the 955L offered improved hydraulic response, better operator visibility, and a more robust undercarriage than its predecessors. It was widely used in construction, quarrying, and land clearing, with thousands of units sold globally. The 955L’s reputation for durability made it a favorite among owner-operators, especially in Europe and North America.

Initial Condition and Engine Diagnosis

One recently acquired 955L had been sitting idle for two years due to a cylinder head failure. The engine showed signs of combustion gas leaking into the coolant circuit, a classic symptom of head gasket failure or cracked cylinder head. Upon inspection, visible cracks were found between the valves on all three cylinders. While the pre-combustion chambers appeared intact, the severity of the cracks raised concerns about coolant intrusion and long-term reliability.

Technicians noted that cracks between valves are often terminal for cast iron heads, especially if they extend into the water jacket. Welding such cracks is risky and rarely holds under operating pressure. In this case, the head had been removed but not repaired, and the loader was purchased for €2000—low enough to justify experimentation.

Transport Strategy and Temporary Assembly

To move the loader, the owner planned to reassemble the engine temporarily using a semi gasket set. The goal was to start the machine just long enough to load it onto a trailer, transport it home, and unload it. Several experienced mechanics advised against adding coolant during this process, fearing hydrostatic lock if water entered a cracked cylinder. Instead, they recommended dry starting, shutting down immediately after ignition, and repeating only for loading and unloading.

Serial Number and Machine Identification

The machine bore serial numbers 8Y8710 and 64J6418, confirming it as a French-built 955L from the early 1980s. These units typically came with the 48V 3304 engine. The engine arrangement number 6A5545 matched a Caterpillar belt part number 2P2696, which cross-referenced to a 22 mm × 1599 mm V-belt—useful for sourcing replacements from local suppliers.

Undercarriage and Structural Issues

Beyond the engine, the loader had significant undercarriage wear. The idler push rod flanges were broken, and bolts securing the recoil spring brackets were missing. These components are critical for track tension and alignment. The “death spring,” a nickname for the powerful recoil spring, must be properly restrained to avoid dangerous release during disassembly.

The machine also showed signs of poor maintenance: rusted fasteners, pitted cylinder head surfaces, and general neglect. One mechanic speculated that the engine had been run low on coolant and severely overheated, warping the head and accelerating crack formation.

Repair Options and Cost Considerations

Recommendations included:

• Sourcing a used or aftermarket cylinder head for the 3304 engine
• Inspecting pistons, liners, and rings for wear or scoring
• Replacing the undercarriage components, especially idler brackets and recoil spring bolts
• Cleaning and resurfacing the block face before reassembly
• Avoiding investment in welding the head unless as a temporary measure

Aftermarket heads for the 3304 are still available due to the engine’s popularity in generators and industrial equipment. However, costs can exceed €1000, and installation requires careful torque sequencing and coolant pressure testing.

Field Stories and Practical Advice

One retired quarry mechanic recalled a similar case where a 955L was revived with a salvaged head and ran for another 1,500 hours before final retirement. Another operator used a cracked head temporarily for transport, then scrapped the machine after discovering extensive liner corrosion.

A common theme among contributors was the value of the 955L’s mechanical simplicity. Despite its age, the loader remains serviceable with basic tools and mechanical knowledge. However, the cost of full restoration often exceeds the machine’s resale value unless done for personal use or historical preservation.

Final Thoughts

The Caterpillar 955L is a rugged, capable track loader with a long service history. Reviving a neglected unit requires realistic expectations, especially when facing engine cracks and undercarriage damage. For mechanically inclined owners, temporary repairs may allow safe transport and further evaluation. But for long-term use, investing in a sound cylinder head and restoring critica