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The Series 71 oil pump is mounted on the main bearing caps and is gear-driven directly from the crankshaft. This placement allows it to operate in sync with engine speed, adjusting oil flow to meet lubrication demands at different RPMs.
- Pressure Relief Valve: All Series 71 oil pumps include a built-in pressure relief valve to prevent excessive oil pressure. This valve opens to bypass excess oil back to the pump intake side when pressure exceeds the threshold, typically set at 105 psi (724 kPa), though it may vary slightly by model.
- Scavenging Feature: Certain models, such as those used in marine applications or inclined installations, include a dual-type oil pump with a scavenging function. This feature enables oil to be transferred from the front to the rear of the oil pan during inclined operation, ensuring consistent lubrication even at an angle. The scavenging pump uses additional components like a spacer, extra gears, and dedicated piping.
The oil pump in the Detroit Diesel Series 71 engine serves as the heart of the lubrication system, responsible for drawing oil from the oil pan and distributing it under pressure to all critical engine components. This continuous oil flow not only lubricates moving parts but also dissipates heat and prevents wear on high-friction surfaces. Properly functioning oil pumps are fundamental to engine health, as inadequate lubrication can lead to catastrophic engine failure. Here’s an in-depth look at how the oil pump performs these essential functions.
1. Primary Functions of the Oil Pump
The oil pump performs several critical functions within the Series 71 engine:
- Oil Circulation: The pump draws oil from the sump and circulates it through the engine, supplying each moving component with a consistent flow of oil to reduce friction and wear. This circulation creates a thin oil film that prevents direct metal-to-metal contact, which would otherwise cause rapid wear.
- Heat Management: As oil circulates, it absorbs heat generated by combustion and friction within the engine. The oil pump helps remove this heat by passing oil through the engine’s oil cooler, which then returns the cooled oil to the engine, helping to stabilize temperatures and prevent overheating.
- Pressure Maintenance: The pump maintains the required oil pressure to reach distant components within the engine, such as the camshaft, main bearings, connecting rods, and piston pins. Consistent pressure is crucial for even distribution, ensuring that each part receives the necessary lubrication under various operating conditions.
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2. Oil Flow Pathway and Pressure Regulation
The oil flow pathway in Series 71 engines is designed to ensure that each critical component receives lubrication, with the oil pump as the driving force:
- Oil Drawn from the Sump: The pump begins its cycle by drawing oil from the sump through an inlet screen, which filters out large particles to prevent them from entering the pump.
- Oil Pressure Regulation: As the oil pump operates, it builds pressure based on engine speed. To manage this, a pressure relief valve within the pump housing monitors and controls excess pressure. This valve is crucial, especially during high RPMs, as it opens to bypass oil when the system pressure exceeds approximately 105 psi (724 kPa). The bypassed oil is redirected back to the sump, ensuring pressure levels remain within safe limits and protecting the engine from potential damage caused by excessive force.
- Full-Flow Filtration: The pressurized oil then flows through a full-flow filter, where smaller particles and contaminants are removed. This filtration process prevents abrasive particles from damaging components and maintains oil cleanliness, which is especially important for prolonged engine life.
- Oil Cooling and Return: After filtration, the oil typically flows through an oil cooler, where it dissipates heat before being circulated back into the engine’s oil galleries. This cooling process is essential, as heated oil can lose viscosity, reducing its effectiveness as a lubricant. Once cooled, the oil is directed to key areas, such as the crankshaft bearings, camshaft bearings, and cylinder walls.
3. Specialized Dual Oil Pump with Scavenging for Marine Applications
In specific models of the Series 71, especially those designed for marine or inclined operations, a dual-function oil pump includes a scavenging pump. This pump assists in oil movement from the front to the rear of the oil pan when the engine is operated at an angle.
- Scavenging Feature: When the engine is tilted, gravity pulls the oil toward one end of the pan, which can lead to inconsistent oil pickup. The scavenging pump mitigates this by redirecting oil to ensure it consistently reaches the main pump intake, preventing oil starvation in sloped or marine conditions.
- Additional Components: Engines with this setup incorporate additional screens, spacers, and gears to support the scavenging action. These components must be carefully maintained to ensure continuous oil flow under angled operation.
4. Gear-Driven Mechanism and Variations Across Models
The oil pump in Series 71 engines is driven by the crankshaft, which powers a gear-driven mechanism to sustain the pump’s rotation at varying speeds, directly linked to engine RPM.
- Drive and Driven Gears: The drive gear attached to the crankshaft rotates the driven gear in the oil pump. This setup ensures consistent oil flow that adjusts dynamically with engine speed. The exact length of the drive gear varies by model—three- and four-cylinder engines require a 6-15/16 inch gear, while six-cylinder models use a 6-15/32 inch gear.
- Clearance Specifications: Maintaining the correct clearance between these gears and the pump housing is essential for efficient oil pressure and flow. In all Series 71 engines, the clearance should be between 0.005 inches and 0.012 inches. Adding or removing shims allows precise adjustment, with each 0.005-inch shim adjusting the clearance by approximately 0.0035 inches.
5. Importance of the Relief Valve and its Maintenance
The relief valve within the oil pump is essential for pressure regulation. It operates by redirecting excess oil back into the intake when pressure surpasses safe levels.
- Valve Spring Tension: The valve spring’s tension determines the pressure threshold, generally set at around 105 psi (724 kPa) across most Series 71 models. This spring’s tension is calibrated to keep oil pressure stable and consistent.
- Common Issues and Inspection: A weak or worn relief valve spring can lead to erratic pressure, potentially causing either oil starvation or excess pressure that can harm engine seals and gaskets. Regular inspection and replacement of the valve spring and plunger ensure that this component functions effectively.
6. Specific Considerations for Engine Operation and Oil Pump Efficiency
The oil pump’s performance and reliability depend on several operational factors:
- Oil Quality and Viscosity: Using high-quality oil with the correct viscosity for the Series 71 engine is essential, as oil that is too thin may not maintain pressure, while oil that is too thick could strain the pump. Regular oil changes based on engine operating hours or condition monitoring are recommended to prevent sludge buildup that could clog the pump or reduce flow efficiency.
- Temperature Effects: As the oil heats up, it becomes thinner, which can affect the pump’s ability to maintain pressure. The oil cooler compensates by lowering the temperature of the oil returning to the engine, helping maintain viscosity and prevent pressure loss, especially during prolonged or high-load operations.
- Clearance and Alignment Adjustments: Maintaining the correct alignment and clearance between the oil pump gears and housing is essential for pressure consistency. For Series 71 engines, adding or removing shims under the pump’s mounting feet is a common way to adjust this clearance. Regularly checking these clearances and adjusting as necessary prevents issues that could impact oil pressure and flow.
By understanding these detailed functions and operations, operators and mechanics of the Detroit Diesel Series 71 can maintain the oil pump’s effectiveness, ensuring reliable lubrication and protection for all engine components. Proper care of the oil pump, including routine checks of its clearances, pressure regulation, and cleanliness, will significantly contribute to the engine’s longevity and performance across various operating conditions.
