Air Scavenging and Blower System For Detroit Diesel 71 Series Inline Engines (271, 371, 471, 671)

October 25, 2024

Air Scavenging and Blower System For Detroit Diesel 271, 371, 471, 671 Engines

Detroit Diesel 471 Blower
This is a picture of a Detroit Diesel 471 Blower. This is a key component for air intake that makes the 2-Cycle system possible.

In the Detroit Diesel Series 71 engine, the air scavenging process is critical for maintaining efficient combustion, especially due to the engine’s two-stroke cycle. The blower plays a central role in ensuring that the engine receives a fresh charge of air while exhaust gases are expelled effectively.

Blowers For Detroit Diesel 71 Series Inline Engines: 

Blower Function in Air Scavenging:

  1. Role of the Blower:
    • The blower forces air into the cylinder through intake ports as the piston reaches the bottom of its power stroke. This process helps remove residual exhaust gases from the previous combustion cycle while simultaneously filling the cylinder with fresh air, essential for proper combustion.
  2. Timing and Efficiency:
    • Since the two-stroke engine must complete its entire cycle in two strokes, the timing and efficiency of the blower are critical to maintaining optimal engine performance. If the blower does not deliver sufficient air, or if exhaust gases are not fully expelled, the engine can experience incomplete combustion, power loss, or higher emissions.

Critical Tolerances for Blower Components:

  1. Blower Rotor-to-Housing Clearance:
    • The clearance between the blower rotors and the housing is vital for maintaining the efficiency of air delivery. Excessive clearance can result in reduced air pressure and inefficient scavenging. The rotor-to-housing clearance should typically be within 0.005 to 0.010 inches (0.127 to 0.254 mm).
    • Measurement Process: Use a feeler gauge to measure the clearance between the rotors and housing. If the clearance exceeds these limits, inspect for wear on the rotors and housing, and repair or replace as necessary.
  2. Blower End Play:
    • The axial movement (end play) of the blower rotors must be kept within tight tolerances to ensure smooth operation and prevent damage. The end play should generally be between 0.002 to 0.006 inches (0.051 to 0.152 mm).
    • Measurement Process: Use a dial indicator to measure the axial movement of the blower rotors. Excessive end play may indicate worn bearings or misalignment, and should be corrected to avoid damaging the blower.
  3. Blower Bearing Inspection:
    • Inspect the blower bearings for wear or play, as worn bearings can lead to improper rotor alignment and reduce the blower’s ability to efficiently deliver air. Bearings should be replaced if excessive play or wear is detected.

Blower Drive and Timing Mechanism:

  1. Blower Drive Inspection:
    • The blower is driven by either gears or a belt connected to the engine’s timing mechanism. Regularly inspect the drive components for wear, proper tension, and alignment. A worn drive can lead to poor blower performance, resulting in insufficient air delivery or timing issues with air scavenging.
  2. Timing Synchronization:
    • Ensure that the blower timing is synchronized with the engine’s operation. Incorrect timing can result in air being delivered too early or too late in the cycle, affecting combustion efficiency. For gear-driven systems, inspect the gear teeth for wear and check for proper engagement.
  3. Lubrication of Blower Drive:
    • For gear-driven blowers, inspect the lubrication system to ensure that the blower drive gears are adequately lubricated. Lack of lubrication can cause wear and lead to gear failure. Refill or replace lubricants as necessary during regular maintenance.

Blower Inspection and Maintenance:

  1. Visual Inspection:
    • Regularly inspect the blower for debris, dirt, or oil accumulation, which can reduce its effectiveness. Check for damage to the rotors or housing that could affect air delivery. Inspect the blower drive mechanism for proper alignment and wear, ensuring the blower operates without excessive vibration or noise.
  2. Blower Performance Testing:
    • After servicing the blower, perform a test under load to ensure it is delivering the correct air volume. Check for any signs of leakage or improper air pressure that could reduce scavenging efficiency.
  3. Blower Reassembly and Torque Specifications:
    • When reassembling the blower after cleaning or maintenance, ensure that all fasteners and bolts are torqued to the manufacturer’s specifications to avoid over- or under-tightening. Typical torque values for blower mounting bolts are 20 to 25 lb-ft (27 to 34 Nm). Proper torque is critical to prevent leaks or mechanical failure.

Step-by-Step Blower Disassembly:

  1. Removing the Blower:
    • Start by disconnecting any associated oil or coolant lines to prevent spills. Loosen the blower’s mounting bolts in a criss-cross pattern to evenly release pressure on the housing. Carefully lift the blower off the engine, ensuring not to damage the intake manifold or gasket.
    • Inspect all mating surfaces for carbon deposits or damage that may affect reassembly.
  2. Disassembling the Blower:
    • If the blower needs internal cleaning or repair, disassemble the unit by carefully removing the rotor housing and separating the rotors. Pay close attention to rotor orientation to ensure they are reinstalled correctly. Clean each component thoroughly before reassembly, removing carbon, oil, and debris.
  3. Inspecting Components:
    • During disassembly, inspect each component, such as the rotors, drive gears, bearings, and seals, for signs of wear. Replace any parts that show wear beyond the specified tolerances.
  4. Reassembly:
    • After cleaning and inspecting the blower, reassemble the components in the reverse order, ensuring proper alignment of the rotors and gears. Torque all fasteners to the recommended specifications and apply any necessary gaskets or seals before reinstalling the blower onto the engine.

Common Symptoms of Blower Problems:

  1. Loss of Power: If the blower is not delivering sufficient air, the engine may experience a noticeable loss of power. This could be due to worn rotors, damaged drive gears, or excessive clearance between the rotors and housing.
  2. Black Smoke from Exhaust: Incomplete combustion due to inefficient air scavenging can cause black smoke to be emitted from the exhaust. This is often a sign that the blower is not providing enough fresh air to clear the exhaust gases.
  3. Unusual Noise or Vibration: If the blower is vibrating excessively or making unusual noises, it may indicate worn bearings, misaligned rotors, or damage to the blower housing.
  4. High Exhaust Gas Temperatures: If the blower is not removing exhaust gases efficiently, it can cause an increase in exhaust gas temperatures, leading to engine overheating and potential damage.

By maintaining proper blower performance, including inspecting key tolerances, ensuring synchronization with the engine timing, and regularly servicing the air intake system, engine operators can ensure efficient air scavenging in the Detroit Diesel Series 71 engine. This helps sustain engine performance, reduce fuel consumption, and minimize emissions.

 

Please follow and like us:
error
fb-share-icon
Tweet
fb-share-icon
RSS
Follow by Email
Facebook
Twitter