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OIL PUMPS The oil pump may be located in the oil pan or mounted to the front of the engine (Fgr__72). Its purpose is to supply oil to cool, clean, and lubricate the various moving parts in the engine. The pump is normally driven by the crankshaft and creates suction to draw oil from the oil pan through a strainer. The pump's suction creates pressure that forces the oil through the oil filter to various passages. The oil then returns to the oil pan. An oil pump does not create oil pressure; it merely moves oil from one place to another. Oil pumps are positive displacement pumps; that is, the amount of oil that leaves the pump is the same amount that enters it. Output volume is proportional to pump speed. As engine rpm increases, pump output also increases. As the oil leaves the pump, it passes through many passages. These passages restrict oil flow. These restrictions are what cause oil pressure. Small passages cause the pressure to increase; larger ones decrease the pressure. This is why excessive bearing clearances will decrease oil pressure. The increased clearances reduce the resistance to oil flow and, consequently, increase the volume of oil circulating through the engine. This decreased resistance and increased volume lower the pressure of the oil. The ability of an oil pump to deliver more than the required volume of oil is a safety measure to ensure lubrication of vital parts as the engine wears. Oil pressure is also determined by the viscosity and temperature of the oil. High-viscosity oil has more flow resistance than low-viscosity oil. Types of Oil Pumps Oil pumps are driven by the camshaft or crank shaft. In newer engines, the pump is driven by the crankshaft. Integral pumps are driven directly by the crankshaft, and others are driven by a chain or gear. How the pump is driven is dictated by the location of the pump. Some oil pumps have an intermediate or drive shaft that is driven by a gear on the camshaft. Other pumps are driven by an auxiliary shaft meshed with the camshaft. The most commonly used oil pumps are the rotor and gear types. A typical rotor-type pump (Fgr__73) has an inner rotor and an outer rotor, which is driven by the inner rotor. The outer rotor always has one more lobe than the inner rotor. When the rotors turn and the rotors' lobes unmesh, oil is drawn into that space. As the rotors continue to turn, the oil becomes trapped between the lobes, cover plate, and top of the pump cavity. It’s then forced out of the pump body by the meshing of the lobes. This squeezes the oil out and directs it through the engine. The amount of oil forced out of the pump depends on the diameter and thickness of the pump's rotors. Gear-type pumps use a drive gear, which is connected to an input shaft, and a driven gear. Both gears trap oil between their teeth and the pump cavity wall. As the gears rotate, oil is forced out as the gear teeth unmesh. The output volume per revolution depends on the length and depth of the gear teeth. Another style of gear-type oil pump uses an idler gear with internal teeth that spins around the drive gear. In this style of pump, often called a crescent or trochoidal type, the gears are eccentric (Fgr__74). That is, as the larger gear turns, it walks around the smaller one, moving the oil in the space between. The rotor type moves a greater volume of oil than the gear type because the space in the open lobe of the outer rotor is greater than the space between the teeth of the gears of a gear-type pump. At times, high-volume pumps are installed. These pumps provide more oil flow. They don’t provide higher pressures. High-volume pumps have larger gears or rotors. The increase in oil volume is proportional to the increase in the size of the gears. Gears that are 20% larger will provide 20% more oil volume. === Inner rotor; Outer rotor; Pump cover; Pump housing; Relief valve; Spring O-ring; Spring seat Fgr__73 A rotor-type oil pump. Fgr__74 A gear-type oil pump. === Pressure Regulation The faster an oil pump turns, the more oil it will move. Therefore, its output pressure increases. A pressure-regulating (relief) valve is used to control the pump's maximum pressure. Excessive oil pres sure can lead to poor lubrication due to the oil blowing past parts rather than flowing over them. A pressure regulator valve is loaded with a closely calibrated spring that allows oil to bleed off at a given pressure. When the pressure from the pump reaches a preset level, a check valve, ball, or plunger unseats and allows the oil to return to either the inlet side of the pump or to the crankcase. High-pressure oil pumps are basically stock pumps with a stronger relief valve spring. The spring delays the opening of the valve until a higher pressure is reached. OIL PUMP SERVICE Many technicians install a new or rebuilt oil pump on each engine they rebuild. Although the oil pump is probably the best lubricated part of the engine, it’s lubricated before the oil passes through the filter. Therefore, it can experience premature failure due to dirt or other materials entering the pump. Foreign particles can cause the following: 1. Fine abrasive particles gradually wear the surfaces, causing a reduction in efficiency. 2. Hard particles larger than the clearances can cause scoring as they pass through, finally resulting in seizure. 3. Large particles will physically lock up the pump. Of course, when the pump seizes or locks up, the gears or the drive shaft will be twisted or sheared off. Inspection: The oil pump should be carefully inspected. Carefully remove the pressure relief valve and note the direction it’s pointing to so it can be reinstalled in its proper position. If the relief valve is installed backward, the pump won’t be able to build up pressure. Inspect the relief valve spring for signs of collapsing or wear. Check the tension of the spring according to specifications. Also check the piston for scores and free operation in its bore. Remove the housing bolts, then remove the cover from the housing. Inspect the gears or rotors and the pump housing for scoring or other damage. Replace the oil pump if any are found. CAUTION! Always follow the manufacturer's procedure for servicing or replacing an oil pump. Mark the gear teeth so they can be reassembled with the same tooth indexing (Fgr__75). The gears and rotors of some pumps are marked by the factory. Once all parts have been removed, clean them and dry them off with compressed air. SHOP TALK -- Use a paint stick or other nonviolent means to mark the gears. If a center punch must be used, file down the raised material around the indent before reassembling the pump. The raised edges may cause interference and wear if they are not removed. Inspect the pump gears or rotors for chipping, galling, pitting, or signs of abnormal wear. Examine the housing bores for similar signs of wear. If any part of the housing is scored or noticeably worn, replace the pump assembly. === Fgr__76 Measuring the outer rotor with an outside micrometer. Fgr__77 Checking clearance between the outer rotor and pump body. By Chrysler LLC Fgr__75 Mark the gear teeth so they can be reassembled with the same indexing. === Check the mating surface of the pump cover for wear. If the cover is excessively worn, scored, or scratched, replace the pump. Use a feeler gauge and straightedge to check its flatness. There are specifications for the amount of acceptable warpage. If the cover is excessively warped, replace the pump. Use a micrometer to measure the diameter and thickness of the rotors (Fgr__76). If these dimensions are less than the specified amount, the rotors or the pump must be replaced. With rotor pumps, reinstall the rotors into the pump body. Use a feeler gauge to check the clearance between the outer rotor and pump body (Fgr__77). If the housing-to-rotor clearance exceeds specifications, replace the oil pump. If specifications are not available, replace the pump if the measured clearance is greater than 0.012 inch (0.305 mm). Position the inner and outer rotor lobes so they face each other. Measure the clearance between them with a feeler gauge (Fgr__78). A clearance of more than 0.010 inch (0.2540 mm) is unacceptable and the pump should be replaced. The timing case position. If the relief valve is installed backward, the pump won’t be able to build up pressure. Inspect the relief valve spring for signs of collapsing or wear. Check the tension of the spring according to specifications. Also check the piston for scores and free operation in its bore. Remove the housing bolts, then remove the cover from the housing. Inspect the gears or rotors and the pump housing for scoring or other damage. Replace the oil pump if any are found. CAUTION! Always follow the manufacturer's procedure for servicing or replacing an oil pump. Mark the gear teeth so they can be reassembled with the same tooth indexing (Fgr__75). The gears and rotors of some pumps are marked by the factory. Once all parts have been removed, clean them and dry them off with compressed air. === Fgr__76 Measuring the outer rotor with an outside micrometer. Fgr__77 Checking clearance between the outer rotor and pump body. By Chrysler LLC Fgr__75 Mark the gear teeth so they can be reassembled with the same indexing. === SHOP TALK -- Use a paint stick or other nonviolent means to mark the gears. If a center punch must be used, file down the raised material around the indent before reassembling the pump. The raised edges may cause interference and wear if they are not removed. Inspect the pump gears or rotors for chipping, galling, pitting, or signs of abnormal wear. Examine the housing bores for similar signs of wear. If any part of the housing is scored or noticeably worn, replace the pump assembly. Check the mating surface of the pump cover for wear. If the cover is excessively worn, scored, or scratched, replace the pump. Use a feeler gauge and straightedge to check its flatness. There are specifications for the amount of acceptable warpage. If the cover is excessively warped, replace the pump. Use a micrometer to measure the diameter and thickness of the rotors (Fgr__76). If these dimensions are less than the specified amount, the rotors or the pump must be replaced. With rotor pumps, reinstall the rotors into the pump body. Use a feeler gauge to check the clearance between the outer rotor and pump body (Fgr__77). If the housing-to-rotor clearance exceeds specifications, replace the oil pump. If specifications are not available, replace the pump if the measured clearance is greater than 0.012 inch (0.305 mm). Position the inner and outer rotor lobes so they face each other. Measure the clearance between them with a feeler gauge (Fgr__78). A clearance of more than 0.010 inch (0.2540 mm) is unacceptable and the pump should be replaced. The timing case and gear thrust plate might also be worn. Excessive clearance can limit pump efficiency. Replace them as necessary. On a gear-type pump, measure the clearance between the gear teeth and pump housing. Take several measurements at various locations around the housing and compare the readings. If the clearance at any point exceeds 0.005 inch (0.0762 mm), replace the pump. On both gear-type or rotor-type oil pumps, make sure the housing surface is clean and free of gasket material before measuring the end clearance of the gears or rotors. Place a straightedge across the pump housing and measure the clearance between the straightedge and gears (Fgr__79). The desired end play clearance should not exceed 0.003 inch (0.1270 mm). Fgr__78 Measuring clearance between the inner and outer rotor lobes. By Chrysler LLC Pump housing Outer rotor Fgr__79 Check the housing-to-rotor clearance at the (A) rotors and (B) the housing. Some manufacturers recommend that liquid thread lock be applied to the pump housing bolts. Always check the service manual before doing this. Install the cover and tighten the bolts to specifications. The gasket that is used to seal the end housing is also designed to provide the proper clearance between the gears and the end plate. Don’t substitute another gasket or make a gasket to replace the original one. If a precut gasket was not originally used, seal the end housing with a thin bead of anaerobic sealing material. Turn the input shaft or gear by hand. It should rotate easily. If it does not and the pump passed all tests, replace the pump. Remove the old oil seal from the oil pump. Install a new seal into the pump housing. Make sure all mating surfaces of the pump are clean, undamaged, and dry. If the pump uses a hexagonal drive shaft, inspect the pump drive and shaft to make sure that the corners are not rounded. Check the drive shaft-to housing clearance by measuring the OD of the shaft and the ID of the drive. === Fgr__80 Oil pump pickup. Chrysler LLC. Oil pump case Crankshaft Outer rotor Inner rotor Relief valve Oil pan Oil screen Pickup tube === The pickup screen (Fgr__80) is normally replaced when an engine is rebuilt. It’s important that the pickup is positioned properly. This will avoid oil pan interference and ensure that the pickup is always submerged in oil. When installing the pickup tube, be sure to use new gaskets and seals. Air leaks on the suction side of the oil pump can cause the pressure relief valve to hammer back and forth. Over time, this will cause the valve to fail. Air leaks can also cause oil aeration, foaming, marginal lubrication, and premature engine wear. Care should be taken to make sure that all parts on the suction side of the pump fit tightly and that there is no place for air leakage. Air leakage often comes from cracked seams in the pickup tube. INSTALLING THE OIL PUMP The pump should be primed before assembly. The preferred way to do this is to submerge the pump in clean engine oil. Make sure the inlet port is fully in the oil. Then turn the pump by hand until you see oil flow from the outlet of the pump. The use of heavy lubricants inside the oil pump is not recommended because they don’t circulate easily and can cause oil starvation to critical parts when the engine is first started. Crankshaft-Driven Pump--The installation of a typical crankshaft-driven oil pump is as follows: 1. Install a new oil seal into the pump. 2. Apply liquid gasket evenly to the pump's mating surfaces on the block. 3. Don’t allow the gasket material to dry. 4. Coat the lip of the oil seal and the O-rings with oil. 5. Align the inner rotor with the crankshaft. 6. Install and tighten the oil pump. 7. Clean all excess grease on the snout of the crankshaft. 8. Install the oil pickup. Cam-Driven Pumps: The installation of a typical camshaft-driven oil pump is as follows: 1. Apply a suitable sealant to the pump and block. 2. Make sure that the drive gears are properly meshed and that the drive shaft is seated in the pump. 3. Install the pump to its full depth and rotate it back and forth slightly to ensure proper positioning and alignment through the full surface of the pump and the block machined interface surfaces. 4. Once installed, tighten the bolts or screws. The pump must be held in a fully seated position while installing the bolts or screws. 5. Install the oil pump inlet tube and screen assembly. Distributor-Driven Pump When installing an older style, distributor-driven oil pump, position the drive shaft into the distributor socket. The stop on the shaft should touch the roof of the crankcase when the shaft is fully seated. With the stop in position, insert the drive shaft into the oil pump. Install the pump and shaft as an assembly. Make sure that the drive shaft is seated in the pump drive. Then tighten the oil pump, attaching screws to torque specifications. Install the pump inlet tube and screen assembly. === Next: Example Study Prev.: Oil Pumps Home Article Index top of page |
