6 hours ago
The History of the Cat 933 and Its Powertrain
The Caterpillar 933 track loader was introduced in the mid-20th century as part of Caterpillar’s push to offer compact, versatile machines for construction, agriculture, and industrial use. Designed to bridge the gap between small dozers and full-sized loaders, the 933 featured a rugged undercarriage, mechanical simplicity, and a reliable diesel powerplant. Early models were powered by the Caterpillar D320 engine—a naturally aspirated, four-cylinder diesel known for its torque and longevity.
Caterpillar Inc., founded in 1925, had by then become a global leader in earthmoving equipment. The 933 was widely adopted across North America and Europe, with thousands sold between the 1950s and 1970s. Its popularity stemmed from its ability to handle grading, loading, and light dozing tasks with minimal maintenance. However, as time passed, sourcing parts for the D320 engine became increasingly difficult, especially for internal components like crankshaft bearings.
Understanding the D320 Engine and Its Bearing System
The D320 engine uses a conventional crankshaft supported by main bearings and a rear thrust bearing. These bearings are critical for maintaining crankshaft alignment and absorbing axial loads during operation.
Terminology:
Challenges in Sourcing and Verifying Parts
Finding a standard rear main bearing for the D320 engine can be frustrating. Many listings online, including aftermarket suppliers, may carry the correct part number but fail to clarify the bearing size. In one case, a bearing labeled as 7M9283 was marked ".020 undersize" by hand—raising concerns about accuracy and compatibility.
Best practices for sourcing:
Field Anecdote from Pennsylvania
A retired field serviceman in Central Pennsylvania faced this exact dilemma while restoring a Cat 933. After locating a bearing with the correct part number but questionable sizing, he hesitated to install it. Drawing on decades of experience, he recalled that Caterpillar never reused part numbers across different sizes. He ultimately chose to call a trusted supplier and confirmed that the bearing he needed was indeed standard. His caution paid off—avoiding a costly teardown and preserving the integrity of the rebuild.
Technical Recommendations and Rebuild Tips
When rebuilding the D320 engine:
To extend the life of the D320 engine and its bearings:
The Caterpillar 933 track loader and its D320 engine represent a durable legacy of mid-century engineering. While parts like the rear main bearing can be difficult to source, careful verification and mechanical diligence ensure successful rebuilds. With proper maintenance and attention to detail, these machines continue to serve faithfully—decades after they first rolled off the assembly line. For those committed to preserving classic iron, the hunt for parts is part of the journey, and every successful repair is a tribute to the machine’s enduring design.
The Caterpillar 933 track loader was introduced in the mid-20th century as part of Caterpillar’s push to offer compact, versatile machines for construction, agriculture, and industrial use. Designed to bridge the gap between small dozers and full-sized loaders, the 933 featured a rugged undercarriage, mechanical simplicity, and a reliable diesel powerplant. Early models were powered by the Caterpillar D320 engine—a naturally aspirated, four-cylinder diesel known for its torque and longevity.
Caterpillar Inc., founded in 1925, had by then become a global leader in earthmoving equipment. The 933 was widely adopted across North America and Europe, with thousands sold between the 1950s and 1970s. Its popularity stemmed from its ability to handle grading, loading, and light dozing tasks with minimal maintenance. However, as time passed, sourcing parts for the D320 engine became increasingly difficult, especially for internal components like crankshaft bearings.
Understanding the D320 Engine and Its Bearing System
The D320 engine uses a conventional crankshaft supported by main bearings and a rear thrust bearing. These bearings are critical for maintaining crankshaft alignment and absorbing axial loads during operation.
Terminology:
- Main Bearing: A precision-machined shell that supports the crankshaft and allows it to rotate smoothly within the engine block.
- Undersize Bearing: A bearing with reduced internal diameter, used when the crankshaft journals have been machined down due to wear.
- Thrust Bearing: A bearing that controls forward and backward movement of the crankshaft, preventing endplay.
Challenges in Sourcing and Verifying Parts
Finding a standard rear main bearing for the D320 engine can be frustrating. Many listings online, including aftermarket suppliers, may carry the correct part number but fail to clarify the bearing size. In one case, a bearing labeled as 7M9283 was marked ".020 undersize" by hand—raising concerns about accuracy and compatibility.
Best practices for sourcing:
- Always cross-reference part numbers with an official Caterpillar parts manual.
- Confirm bearing size with the seller before purchase.
- Avoid listings with handwritten modifications or unclear provenance.
- Consider contacting reputable suppliers like Regal or Machinery Trader for verified inventory.
Field Anecdote from Pennsylvania
A retired field serviceman in Central Pennsylvania faced this exact dilemma while restoring a Cat 933. After locating a bearing with the correct part number but questionable sizing, he hesitated to install it. Drawing on decades of experience, he recalled that Caterpillar never reused part numbers across different sizes. He ultimately chose to call a trusted supplier and confirmed that the bearing he needed was indeed standard. His caution paid off—avoiding a costly teardown and preserving the integrity of the rebuild.
Technical Recommendations and Rebuild Tips
When rebuilding the D320 engine:
- Measure crankshaft journals with a micrometer to determine wear.
- Use plastigauge to verify bearing clearance during assembly.
- Torque bearing caps to factory specifications using a calibrated wrench.
- Apply assembly lube to all bearing surfaces before startup.
- Inspect oil passages for debris or blockages that could starve the bearings.
- Install an oil pressure gauge to monitor bearing health.
- Use high-zinc diesel-rated oil for better wear protection.
- Add a magnetic drain plug to capture metal particles.
To extend the life of the D320 engine and its bearings:
- Change oil every 100 hours or seasonally.
- Replace oil filters at each change and inspect for metal shavings.
- Avoid prolonged idling, which can reduce oil pressure and increase wear.
- Store the machine indoors or under cover to prevent moisture intrusion.
- Join vintage equipment forums and owner groups to share sourcing leads.
- Keep a detailed log of part numbers and suppliers for future reference.
- Consider purchasing a second engine or parts machine for long-term spares.
The Caterpillar 933 track loader and its D320 engine represent a durable legacy of mid-century engineering. While parts like the rear main bearing can be difficult to source, careful verification and mechanical diligence ensure successful rebuilds. With proper maintenance and attention to detail, these machines continue to serve faithfully—decades after they first rolled off the assembly line. For those committed to preserving classic iron, the hunt for parts is part of the journey, and every successful repair is a tribute to the machine’s enduring design.
