Diagnosing Cam Gear Failure on the Bobcat 773G Loader

[MikePhua]

The Bobcat 773G and Its Engine Configuration
The Bobcat 773G is a skid steer loader introduced in the early 2000s by Bobcat Company, a brand with deep roots in compact equipment innovation since the 1950s. The 773G belongs to the G-series, which featured improved hydraulic performance, enhanced operator comfort, and a more refined control layout compared to earlier models. With a rated operating capacity of 1,750 pounds and a turbocharged diesel engine, the 773G became a popular choice for contractors, landscapers, and rental fleets.
Unlike some compact machines that use timing belts to synchronize engine components, the 773G is equipped with a Kubota V2203 engine—a four-cylinder diesel that relies on gear-driven timing. This design eliminates the need for belt replacement intervals but introduces its own set of mechanical vulnerabilities.
Terminology and Component Notes
- Timing Gear: A toothed steel gear that synchronizes the rotation of the camshaft and crankshaft, ensuring proper valve timing.
- Camshaft: A rotating shaft that actuates intake and exhaust valves via rocker arms.
- Press Fit: A mechanical assembly method where components are tightly fitted without fasteners, relying on friction and interference.
- Keyway: A machined slot that accepts a metal key to prevent rotational slippage between shaft and gear.
- Valve Cover: The protective housing over the top of the engine’s cylinder head, enclosing the valve train.
Symptoms Leading to Cam Gear Failure
In one reported case, a 2001 Bobcat 773G with approximately 3,100 operating hours suddenly lost power and shut down. The initial suspicion was fuel starvation or gelled diesel due to cold weather. After thawing the machine and confirming fuel delivery to the injectors, the engine still refused to start. Upon removing the valve cover, the technician observed no movement in the valve train during cranking—indicating a failure in the camshaft drive system.
This symptom typically points to:

• A sheared cam gear
  
• A broken keyway or press-fit failure
  
• Internal gear tooth damage
  
• Camshaft disengagement from the timing system
  

In this case, the cam gear had either stripped its teeth or separated entirely from the shaft, rendering the valve train inactive and preventing combustion.
Repair Strategy and Disassembly Recommendations
To confirm and repair cam gear failure:

• Remove the valve cover and observe valve movement during cranking
  
• If no movement is present, proceed to remove the front engine cover
  
• Inspect the cam gear for missing teeth, cracks, or separation from the shaft
  
• Check the keyway and press-fit tolerance; if the gear spun freely, the key may have sheared
  
• Replace the cam gear with an OEM-grade part and verify proper alignment
  
• Reinstall with correct torque and lubrication, ensuring gear mesh integrity
  
• Rotate the engine manually to confirm valve timing before startup
  

If the gear failure caused collateral damage to the camshaft or bearings, further teardown may be required. Always inspect adjacent components for wear or metal debris.
Preventative Measures and Long-Term Reliability
While gear-driven timing systems are generally more durable than belt-driven ones, they are not immune to failure. To reduce risk:

• Monitor engine oil quality and change at recommended intervals (typically every 250 hours)
  
• Use high-quality diesel fuel and additives in cold climates to prevent hard starts
  
• Avoid excessive cranking during startup; prolonged rotation under load can stress gear teeth
  
• Listen for unusual noises such as grinding or knocking during operation
  
• Inspect valve train components annually, especially in high-hour machines
  

One technician noted that a similar failure occurred on a Kubota-powered generator after a cold start attempt with low oil viscosity. The cam gear spun off the shaft, leading to a full engine rebuild.
Bobcat’s Compact Loader Legacy
Bobcat Company, founded in North Dakota in 1947, revolutionized compact equipment with the invention of the skid steer loader. The 773G was part of a generation that bridged analog simplicity with hydraulic refinement. Its success contributed to Bobcat’s dominance in the compact loader market, with tens of thousands of units sold globally.
The use of Kubota engines in Bobcat machines reflects a long-standing partnership built on reliability and serviceability. Kubota’s gear-driven timing systems are favored for their longevity, though they require precise assembly and maintenance.
Conclusion
Cam gear failure in the Bobcat 773G is a rare but serious issue that can mimic fuel system problems and lead to extended downtime. By understanding the engine’s gear-driven timing architecture and recognizing the signs of mechanical disengagement, operators and technicians can diagnose the fault accurately and restore function. In compact loaders, timing isn’t just about synchronization—it’s the heartbeat of the machine. And when that rhythm breaks, it takes sharp eyes and steady hands to bring it back.