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The ventilating system in the Detroit Diesel 71 Series inline engines (271, 371, 471, and 671) is essential for maintaining clean engine operation by removing harmful vapors generated within the crankcase. These vapors can contain fuel and oil residues, which, if not managed, may contribute to increased wear and potential component damage. A well-maintained ventilation system ensures effective vapor removal, reduces crankcase pressure, and protects against the buildup of sludge and contaminants.

Crankcase Ventilation Process

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The 71 Series engines employ a continuous, pressurized ventilation system that allows for controlled venting of crankcase gases:

• Airflow Path: Air is pressurized in the crankcase by a small amount of air seeping past the piston rings from the airbox. This air carries crankcase vapors up through the flywheel housing, eventually entering the valve compartment via passages in the lifter brackets and vent castings.
• Vapor Release: These vapors are drawn off through a breather attached to the valve rocker cover or, in some configurations, through a breather on the side of the cylinder block. This system maintains slight pressure within the crankcase, aiding in consistent vapor removal without permitting contaminants to accumulate.

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Maintenance of Breather Pipes

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Routine maintenance of breather pipes is critical to ensure they remain clear of any blockages that might restrict the venting process. Blockages can lead to increased crankcase pressure, which may force oil past seals and contribute to leaks and contamination.

• Inspection and Cleaning Frequency: Inspect and clean the breather pipes at every oil change or every 150-200 hours of engine operation, especially in environments with high dust or particulate matter.
• Cleaning Process:
  • Disassemble the Breather Pipe and Baffle: Remove the breather tube from the governor or the baffle from the cylinder block.
  • Wash with Solvent: Use a suitable cleaning solvent to dissolve oil and sludge deposits inside the breather tube. This will help restore clear passages for airflow.
  • Dry with Compressed Air: After washing, dry the components using compressed air at a safe pressure of no more than 40 psi. Use eye protection during this step to avoid injury.

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Steel Mesh Pad Cleaning

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Some 71 Series engines are equipped with a steel mesh pad within the ventilation system to trap and filter out contaminants before vapors are released. Regular cleaning of this mesh pad is essential for maintaining proper airflow.

• Frequency of Cleaning: Remove and clean the steel mesh pad at least every 500 hours of operation or sooner if the engine operates in particularly dirty environments.
• Cleaning Procedure: Wash the mesh in a solvent designed for engine components, followed by a thorough rinse and drying with compressed air. Ensure the mesh is free of any obstructions before reinstalling.

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Closed Crankcase Vapor Collector System (Optional)

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For certain marine applications, the 71 Series engines, particularly the 6-71 model, can be equipped with an optional closed crankcase vapor collector system. This system further reduces environmental impact by routing crankcase vapors back into the air intake rather than releasing them into the atmosphere.

• System Components:
  • Collector Assembly: Mounted on the inlet side of the turbocharger, this assembly includes an air separator that captures oil particles, allowing the remaining vapors to blend with incoming turbocharger air.
  • Oil Drain Tube and Check Valve: Captured oil drains back to the crankcase via an oil drain tube equipped with a check valve to prevent backflow.
• Maintenance Guidelines for the Closed System:
  • Replace Filter and Vacuum Limiter: When the air inlet restriction indicator shows red, indicating maximum allowable system restriction, replace or clean the filter and vacuum limiter. This should be done every 1,500 hours or every two years, whichever comes first.
  • Cleaning: For filters that are designed to be cleaned, use fluids specifically intended for this purpose. Coat the filter with oil after cleaning to restore its dirt-trapping capability. A service kit, such as the Walker Engineering DDF-9000 kit, is recommended for this procedure.

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By following these maintenance practices for the ventilation system, operators of Detroit Diesel 71 Series engines can ensure consistent crankcase pressure, effective vapor removal, and reduced risk of contamination. Regular inspection and cleaning of breather pipes, steel mesh pads, and optional vapor collectors extend the life of the engine, improve performance, and support environmental compliance, especially in marine applications.