Injector Timing on the Detroit Diesel 6V92TA

[MikePhua]

The Legacy of the 6V92TA Engine
The Detroit Diesel 6V92TA is part of the iconic 92 Series, a family of two-stroke diesel engines introduced in the 1970s by Detroit Diesel Corporation, originally a division of General Motors. The 6V92TA is a turbocharged and aftercooled six-cylinder engine arranged in a V-block configuration, displacing 552 cubic inches. Known for its high power-to-weight ratio and distinctive sound, the 6V92TA powered buses, fire trucks, military vehicles, and construction equipment throughout the 1980s and 1990s.
By the time production tapered off in the early 2000s, Detroit Diesel had sold hundreds of thousands of 92 Series engines worldwide. The 6V92TA remains popular among restoration enthusiasts and operators of legacy fleets due to its mechanical simplicity and robust performance.
Understanding Injector Timing in Two-Stroke Diesels
Injector timing in a two-stroke diesel like the 6V92TA is critical to combustion efficiency, emissions control, and engine longevity. Unlike four-stroke engines, which have distinct intake and exhaust strokes, two-stroke diesels rely on precise synchronization between fuel injection and piston position to avoid overlap and ensure complete combustion.
Terminology notes:

• Injector timing: The calibrated setting that determines when fuel is injected relative to piston position.
  
• Cam follower: A mechanical component that rides on the camshaft and actuates the injector plunger.
  
• Timing pin: A tool used to lock the crankshaft at top dead center (TDC) for accurate timing.
  
• Rocker arm height: The vertical distance used to set injector timing, measured with a gauge.
  

Symptoms of Incorrect Injector Timing
Improper injector timing can lead to a range of performance issues:

• Hard starting or no start
  
• Excessive white or black smoke
  
• Poor throttle response
  
• Engine knock or misfire
  
• Elevated exhaust temperatures
  
• Reduced fuel economy
  

In one case from a transit fleet in Chicago, a 6V92TA-powered bus began producing thick white smoke and struggled to climb hills. After checking compression and fuel delivery, technicians discovered the injector timing was advanced by 0.020 inches beyond spec. Resetting the timing restored full power and eliminated the smoke.
Setting Injector Timing on the 6V92TA
Injector timing on the 6V92TA is set using a height gauge and a timing pin. The process involves:

• Rotating the crankshaft to TDC using the timing pin
  
• Identifying the correct cylinder in firing order
  
• Measuring the injector plunger height using a calibrated gauge
  
• Adjusting the rocker arm screw to achieve the specified height
  
• Locking the adjustment with the jam nut
  
• Repeating the process for all cylinders in firing sequence
  

Typical injector timing height for the 6V92TA ranges from 1.460 to 1.484 inches depending on application and injector type. Always refer to the engine tag and service manual for exact specifications.
Tools and Techniques for Precision
Essential tools include:

• Detroit Diesel timing pin
  
• Injector height gauge (marked in thousandths of an inch)
  
• Torque wrench for rocker arm lock nuts
  
• Feeler gauges for valve lash verification
  
• Clean rags and solvent for removing carbon deposits
  

Technicians should work in a clean environment and rotate the engine manually to avoid overshooting TDC. Using a dial indicator to confirm piston position adds precision, especially on rebuilt engines.
Field Story from a Logging Operation
In 2008, a logging crew in British Columbia rebuilt a 6V92TA powering a yarder winch. After reassembly, the engine ran rough and overheated under load. The crew suspected fuel contamination but found none. A retired mechanic was called in and discovered the injector timing was set using the wrong gauge—off by 0.030 inches. After correcting the timing, the engine ran smoothly and completed the season without further issues.
Preventive Maintenance and Recommendations
To maintain optimal injector timing:

• Check timing during major overhauls or injector replacement
  
• Inspect cam followers and rocker arms for wear
  
• Use OEM injectors and avoid mixing types
  
• Keep timing tools calibrated and clean
  
• Document timing settings and engine serial numbers for future reference
  

Operators should monitor exhaust color and fuel consumption as indirect indicators of timing drift. In high-hour engines, timing may shift due to camshaft wear or follower degradation.
Modern Comparisons and Electronic Controls
While the 6V92TA uses mechanical timing, modern Detroit Diesel engines like the Series 60 rely on electronic control modules (ECMs) to manage injection timing dynamically. These systems adjust timing based on load, RPM, and temperature, improving emissions and fuel efficiency.
Retrofitting a 6V92TA with electronic injectors is not feasible due to its mechanical cam-actuated design. However, maintaining precise mechanical timing can yield comparable reliability and performance in legacy applications.
Conclusion
Injector timing on the Detroit Diesel 6V92TA is a foundational aspect of engine performance. With the right tools, careful measurement, and attention to detail, technicians can ensure smooth operation and extend the life of this iconic two-stroke diesel. In a world of electronic engines, the 6V92TA remains a testament to mechanical precision and enduring power.