Oil Pump Specifications and Clearances For Oil Pumps For Detroit Diesel 71 Series Inline Engines (271, 371, 471, 671)

October 30, 2024

Oil Pump Specifications and Clearances For Oil Pumps For Detroit Diesel 71 Series Inline Engines (271, 371, 471, 671)

- Maintaining specific clearances, torque values, and settings is essential for the oil pump in the Series 71 engine to function efficiently and reliably. Each specification contributes to achieving the desired oil pressure, ensuring smooth gear operation, and minimizing wear on internal parts. Following these guidelines precisely is key to preserving oil pump and engine health.
  
  1. Gear-to-Housing Clearance
  
  The clearance between the gears (drive and driven) and the housing is critical for creating the necessary pressure and preventing excessive friction. This clearance affects how efficiently oil is pumped through the system.
  - Required Clearance Range: For the Series 71 oil pump, the recommended clearance between the gears and the housing is 0.005 to 0.012 inches. This clearance range allows for efficient oil flow while preventing gear binding or excessive wear.
  - Measuring Clearance: Use a feeler gauge to measure the gear-to-housing clearance accurately. Insert the gauge between the gears and the housing at several points around the circumference to confirm a consistent clearance. Ensure that the gauge slides smoothly without forcing it, as any resistance could indicate improper clearance.
  - Importance of Accurate Clearance: Too little clearance can cause gears to bind, creating friction and potentially leading to overheating or wear. Conversely, too much clearance can reduce oil pressure by allowing oil to escape around the gears, diminishing the pump’s efficiency.
  2. Shimming for Clearance Adjustment
  
  Shimming is a precise method to adjust gear-to-housing clearance, ensuring that the gears are correctly positioned within the housing. Shims are thin metal spacers placed between the oil pump’s mounting feet and the engine’s main bearing caps to adjust the pump’s position slightly.
  - Shimming Guidelines: Adding or removing shims adjusts the gear clearance incrementally. Adding a 0.005-inch shim changes the clearance by approximately 0.0035 inches. This slight adjustment allows for precise alignment of the gears within the specified range.
  - Procedure for Shimming:
    - Measure the initial clearance with a feeler gauge and determine the necessary adjustment.
    - Add or remove shims based on the measurement, ensuring that the same thickness is added to each mounting foot to maintain even alignment.
    - Re-measure the clearance after adjusting shims to confirm it falls within the 0.005 to 0.012 inches range.
  - Consistent Shimming: Ensure that the same number of shims is placed under each mounting foot. Uneven shimming can misalign the gears, leading to uneven wear and reduced efficiency. Proper shimming ensures consistent clearance, reduces friction, and promotes smooth gear operation.
  3. Torque Specifications for Mounting Bolts
  
  Properly torquing the oil pump’s mounting bolts is essential to secure the pump in place and maintain alignment. Incorrect torque can lead to misalignment, vibrations, and potential oil leaks.
  - Torque Range: For the Series 71 oil pump, mounting bolts should be torqued to 35-39 lb-ft. This torque specification secures the pump without risking overtightening, which could damage the mounting feet or distort the pump housing.
  - Using a Torque Wrench: Use a calibrated torque wrench to achieve precise torque. Gradually tighten the bolts in a cross-pattern to evenly distribute pressure and prevent misalignment. This even distribution helps maintain proper gear alignment and clearance.
  - Retorque Check: After initial installation, it’s advisable to recheck the torque on mounting bolts after the first few hours of engine operation. Vibrations during initial operation can sometimes loosen bolts, and retorquing ensures the pump remains securely mounted.
  4. Relief Valve Setting
  
  The relief valve regulates oil pressure within the pump by opening when pressure exceeds a certain threshold, typically set at 105 psi (724 kPa). Proper calibration of the relief valve is critical for consistent oil pressure and protecting the engine from excessive pressure.
  - Relief Valve Pressure: The relief valve is designed to open when oil pressure reaches approximately 105 psi (724 kPa), allowing excess oil to bypass the pump and return to the sump. This setting protects engine components from potential damage due to over-pressurization.
  - Inspecting the Relief Valve Spring and Plunger: The spring in the relief valve determines the opening pressure. Inspect the spring for any signs of wear, deformation, or loss of tension, as these can affect pressure regulation. The plunger should move freely within its housing to ensure it opens and closes as needed without sticking.
  - Adjusting the Relief Valve: If the spring is worn, replace it with one that matches the original specifications to maintain proper pressure regulation. Regular inspection and replacement as needed are essential for ensuring consistent oil pressure across various engine operating conditions.
  5. Drive Gear Lengths by Engine Model
  
  The drive gear length differs slightly across Series 71 engine models, with different lengths specified for three-, four-, and six-cylinder models to ensure proper alignment and engagement with the crankshaft.
  - Gear Lengths by Model:
    - Three- and Four-Cylinder Models: These models require a drive gear length of 6-15/16 inches. This specific length allows for proper alignment within the pump housing and consistent engagement with the crankshaft.
    - Six-Cylinder Models: Six-cylinder models use a drive gear length of 6-15/32 inches. This variation accounts for the larger crankshaft and ensures correct alignment for optimal pressure and efficient oil flow.
  - Importance of Correct Gear Length: Using the correct gear length for each model is essential for maintaining proper gear alignment and engagement with the crankshaft. Incorrect gear lengths can lead to misalignment, excessive wear on the gears and bushings, and reduced oil pressure.
  - Replacement Gear Selection: When replacing drive gears, always verify that the replacement matches the specified length for the specific engine model. Using an incorrect gear length could lead to operational inefficiencies, pressure fluctuations, or even pump failure.
  6. General Tips for Maintaining Specifications
  
  To ensure all specifications are maintained throughout the oil pump’s service life, consider the following best practices:
  - Recheck Specifications During Routine Maintenance: Regularly measure and confirm that clearances, torque values, and relief valve settings remain within specifications, especially after performing any service work on the pump.
  - Use Quality Replacement Parts: When replacing components such as gears, bushings, or relief valve springs, use parts that meet Detroit Diesel’s original specifications. Quality replacement parts ensure that specifications are maintained and reduce the risk of premature wear or operational inefficiencies.
  - Keep a Log of Adjustments: For engines in heavy-duty or high-stress environments, maintaining a log of clearance adjustments, torque checks, and relief valve replacements provides a useful reference for future maintenance. This log can help identify trends, such as increased wear rates, allowing for proactive adjustments and replacement planning.
  By carefully following these oil pump specifications and clearances, operators of the Detroit Diesel Series 71 engine can maintain efficient oil pressure and consistent lubrication, protecting engine components and extending service life. Accurate adherence to gear clearances, shimming practices, torque specifications, and relief valve settings ensures that the oil pump performs optimally across a range of operating conditions, safeguarding engine health and enhancing reliability.