What Is the Correct Injector and Timing for a Detroit 6V92T in Industrial Applications

[MikePhua]

The Detroit Diesel 92 Series Legacy
The Detroit Diesel 92 Series, introduced in the 1970s, was a two-stroke diesel engine family designed to deliver high power in compact form. Built on the success of the earlier 71 Series, the 92 Series featured larger displacement per cylinder—92 cubic inches—and came in configurations ranging from 6V92 to 12V92. These engines powered everything from transit buses and fire trucks to marine vessels and industrial recyclers.
Detroit Diesel Corporation, originally a division of General Motors, became an independent entity in 1987 and was later acquired by Daimler AG. Over its production life, the 92 Series sold hundreds of thousands of units globally, with the 6V92T (turbocharged) variant being especially popular in heavy-duty applications.
Injector Confusion and Serial Number Discrepancies
A common issue when rebuilding a 6V92T is identifying the correct fuel injector type based on the engine’s serial number. In one case, a technician discovered that a 6V92T installed in a Bomag recycler had 9A90 injectors, while documentation indicated it should use 9B90 injectors. This discrepancy raised questions about timing height, injector compatibility, and whether the engine was originally built for industrial or marine use.
The 9A90 injectors were typically used in 8V92 TA/TTA automotive engines with a timing height of 1.470 inches. The 9B90 injectors were specified for 6V92 TA/TTA automotive engines, timed at 1.475 inches. However, industrial engines often deviate from automotive specs due to different cam profiles, turbo setups, and emission requirements.
Terminology Annotation

• TA/TTA: Turbocharged and Aftercooled configurations, enhancing power and thermal efficiency.
  
• Timing Height: The calibrated distance used to set injector timing, critical for combustion synchronization.
  
• Throttle Delay Mechanism: A hydraulic or pneumatic system that delays throttle response to reduce smoke during turbo spool-up.
  
• Bomag Recycler: A machine used for asphalt and soil stabilization, often powered by high-torque diesel engines.
  

Throttle Delay and Unusual Engine Features
The engine in question featured a throttle delay setup and an atypical thermostat housing, suggesting it may have originated from a marine or coach application. Throttle delay mechanisms are designed to reduce black smoke during acceleration by limiting fuel delivery until the turbocharger reaches optimal speed. This setup is rare in industrial machines but common in marine engines where emissions and visibility are critical.
In the mid-1980s, Detroit Diesel advertised a 565 hp marine version of the 6V92, which may explain the presence of such features in a recycler. The paint matched the host machine, but the internal configuration hinted at a repurposed engine.
Injector Timing Recommendations
When injector charts are unavailable, technicians must rely on safe baseline values. For 9B90 injectors in industrial applications, a timing height of 1.480 inches is considered conservative. This setting may cause slight cold-start smoke but protects piston rings from premature wear due to advanced cam timing.
If the engine shows signs of excessive smoke or poor throttle response, adjustments can be made incrementally:

• Start at 1.480 inches
  
• Monitor exhaust opacity and cylinder temperatures
  
• Adjust in 0.005-inch increments if needed
  

Always verify camshaft part numbers and injector rack settings before finalizing timing.
Rebuild Strategy and Component Sourcing
During overhaul, piston kits were assembled while waiting for the cylinder heads from the machine shop. This staggered approach allows for efficient use of time and ensures that subassemblies are ready for installation. When sourcing injectors, price differences can be significant—9A90s were reportedly double the cost of 9B90s—making correct identification essential.
Recommendations for rebuild include:

• Use OEM or remanufactured injectors with verified flow rates
  
• Replace all seals and gaskets with high-temperature variants
  
• Inspect cam lobes for wear and pitting
  
• Clean and pressure-test cylinder heads before installation
  

Throttle Cylinder Adjustment Procedure
Adjusting the throttle delay mechanism requires careful calibration. The system typically includes a throttle cylinder, delay valve, and linkage. The goal is to synchronize fuel delivery with turbo boost to minimize smoke and prevent engine lugging.
Adjustment steps:

• Disconnect the throttle linkage
  
• Set the delay cylinder to its neutral position
  
• Reconnect linkage with zero preload
  
• Test acceleration under load and observe smoke levels
  
• Fine-tune delay valve to balance responsiveness and emissions
  

In one case, a technician used scanned pages from a Detroit manual to guide the adjustment, restoring smooth throttle response and reducing startup smoke.
Industrial Versus Automotive Calibration
Charts and manuals often focus on automotive configurations, but industrial engines require different calibration. Factors include:

• Load profile (constant vs. variable)
  
• Ambient temperature and altitude
  
• Emission regulations
  
• Turbocharger type and intercooling
  

For example, a 6V92T in a transit bus may use 9B90 injectors at 1.475 inches, while the same engine in a recycler might need 1.480 inches due to higher sustained torque demands.
Final Thoughts
Rebuilding a Detroit 6V92T is as much an art as a science. With injector charts often missing and engines repurposed across industries, technicians must combine experience, documentation, and observation to achieve optimal performance. Whether the engine came from a marine vessel or a coach, its new life in an industrial recycler demands precision and adaptability.
The 92 Series may be out of production, but its legacy lives on in machines that still rely on its unmistakable two-stroke roar. For those who know how to tune them, these engines remain a symbol of mechanical resilience and engineering ingenuity.