1/1/2004
Click on a thumbnail to see the full-size image
Oil Pumps: The Heart of the Engine
By Larry Carley
The oil pump is literally the heart of an engine’s lubrication system. It sucks oil in from the crankcase and pushes it through the filter and oil galleries to the crankshaft and camshaft bearings. A constant supply of oil is needed to support and cool the bearings. If for any reason the pump cannot keep the oil circulating it’s the end of the road for the engine.
An oil pump failure is just as bad as cardiac arrest because the results are almost always fatal. Loss of oil pressure means loss of the protective oil film between the bearings and their journals. With no oil to keep the surfaces apart, the bearings wipe and fail.
A worn oil pump can’t deliver the same volume of oil as a pump with normal clearances. With less flow, there’s less oil pressure, less oil to maintain the oil film in the bearings and less cooling for the bearings. Under heavy load or at idle, there may not be enough oil flow to keep the bearings adequately lubed. The result is wiped bearings and engine failure.
Nothing Lasts Forever
A brand new oil pump is engineered to last the life of the engine, which on late model cars and light trucks is typically 150,000 miles or more. But like any other mechanical component the pump is subject to wear. In fact, the oil pump experiences more wear than most other engine parts because it is the only internal engine component that runs on unfiltered oil.
Think about it. The filter protects the bearings and other internal engine parts by trapping wear particles and debris that end up in the crankcase. But the filter provides no protection whatsoever for the pump because the filter is located after the pump. The oil pump just sucks up whatever is in the crankcase and pushes it along to the filter. The only protection for the pump is a screen at the end of the pickup tube. The screen can stop big chunks of debris but little else. Some pickups even have slits that allow cold oil to bypass the screen when the engine is first started, so if there’s any junk in the oil it will be sucked right into the pump.
Pump failure can occur if anything large enough to jam the gears or rotors enters the pump. This includes metallic debris from bearings or castings, gasket or seal debris, shot peening remnants, glass beads from bead blasting, or anything else that doesn’t belong in the crankcase. With twin-gear pumps, a foreign object that enters the pump can lodge between the close-fitting gears or the gears and housing causing the pump to lock up. Once the gears stop turning, something has to give. Usually the pump shaft twists or shears off. Sometimes a pump seizure tears up the teeth on the camshaft or distributor drive gears depending on how the pump is driven. With front mounted rotor style pumps, debris usually won’t lock up the pump because it is driven directly off the crankshaft, but it can damage or destroy the rotors.
Even if a pump doesn’t fail, it loses efficiency as it wears. Over time, the effects of pumping unfiltered oil takes a toll. Scratches and wear in the gears and pump housing increase clearances and reduce pumping efficiency. The result is a gradual loss of oil flow and oil pressure.
An oil pump, by the way, does not create oil pressure. It pushes oil from one place to another. It is a positive displacement pump that moves oil every time it turns. Oil is incompressible so once it leaves the pump it continues to flow until it encounters resistance in the filter, oil galleries and bearings. It’s the resistance to flow that builds pressure in the oil system. Trying to force oil through a small opening is going to create more resistance and pressure than allowing it to pass freely through a large opening.
A worn pump can’t deliver the same volume of oil as a new pump, so with less flow there’s a drop in oil pressure.
As pressure starts to back up in the oil system, it has to go somewhere. A spring-loaded "pressure relief valve" built in the oil pump (or next to the pump) opens when pressure exceeds a certain limit (typically 50 to 60 psi) and either reroutes oil back into the pump’s inlet or the oil pan. This prevents a dangerous buildup of pressure that could rupture the oil filter or blow out press-fit oil plugs.
At idle, most oil pumps do not produce enough flow to force open the relief valve. Oil pumps that are camshaft driven only turn at half engine speed so output isn’t great at idle and low rpm. Even pumps that are crankshaft driven and turn at engine speed (or double engine speed in a few instances) don’t pump enough oil to overcome the relief valve spring. The relief valve generally only comes into play at higher rpms when the pump’s output pushes more oil into the system than it can handle. Then the relief valve opens to vent oil and limit maximum oil pressure until engine returns to idle or a lower rpm.
Vehicle manufacturers have traditionally recommended a minimum of 10 psi of oil pressure for every 1,000 rpm of engine speed. Using these numbers, most stock engines don’t need any more than 50 to 60 psi of oil pressure. With tighter bearing clearances, pressure goes up requiring less flow from the pump and less parasitic horsepower loss to drive the oil pump.
In racing applications, the old school of thought was more oil pressure was needed to keep the engine lubed. That’s true if bearing clearances are loosened up. But most engine builders today tighten clearances so less oil flow is needed to maintain adequate oil pressure. This approach increases the horsepower output because less power is needed to drive the pump at high rpm.
According to various sources, a stock oil pump is usually more than adequate for modified stock block performance engines. NASCAR engines typically get by just fine with no more than 50 psi of oil pressure at 9,000 rpm! Some top fuel dragster and funny car engines are set up so the oil pump will dump excessive oil pressure at high rpm so more power will be routed to the rear wheels.
High Volume/Pressure
In applications where more oil flow is desired either to increase oil flow and pressure for better bearing lubrication and cooling, an oil pump with longer or larger gears may be installed. The physically larger surface area of the gears pushes more oil through the pump at the same rpm as a stock pump. A high volume oil pump typically flows 20 to 25 percent more oil than a stock pump. The increase in oil flow produces an increase oil pressure at idle, which helps compensate for increased bearing clearances. Consequently, some people may install a high volume pump in a high mileage engine in an attempt to restore normal oil pressure. But oil isn’t metal, and the only real cure for low oil pressure is to replace worn bearings and restore normal clearances.
High pressure oil pumps are another option. A high pressure pump contains a stiffer relief valve spring that does not open until a higher pressure is reached (75 psi or higher). The actual flow rate of a high pressure pump may be no different than a stock pump, or it may be higher if longer gears are used. Either way, the pump will increase the system oil pressure reading at high rpm when the pump is working hard, but it won’t have any effect on idle pressure when the pump is turning slowly.
A high volume or high pressure oil pump may be recommended in engines where bearing clearances are looser than normal, in engines where an auxiliary external oil cooler has been added to improve oil cooling, and in racing engines where a oil accumulator has been installed.
Rebuild or Replace?
When a high mileage engine is being remanufactured, you have the option of rebuilding or replacing the oil pump. No engine builder in their right mind is going to risk a warranty return by reusing a worn pump in a rebuilt engine, so most simply replace the pump. According to Melling Engine Parts, a major supplier of oil pumps and repair kits, most engine builders today replace pumps rather than rebuild them because installing a new pump is quicker, easier and less risky.
Replacing the gears in a twin-gear pump can restore gear-to-gear clearances but not gear-to-housing clearances. The end plate that covers the pump often develops a heavy wear pattern that is most noticeable on the outlet gear side. Regrinding the face of the plate smooth can restore end play tolerances between the plate and gears but it can’t compensate for wear in the housing. Deep scratches or grooves worn into the sides of the housing will leak oil and reduce the pump’s ability to move oil.
In the case of front cover oil pumps on overhead cam engines, the pump turns at engine rpm and generates more flow at idle than crankcase mounted pumps. Consequently, when the pump becomes worn it isn’t always necessary to replace the entire cover assembly – provided the pump housing inside the cover isn’t worn or damaged. A new drive gear can be mounted on the crankshaft and a new rotor installed in the cover to restore normal oil pressure. This approach can usually save you 50 percent or more over replacing the entire cover assembly.
In cases where an engine has experienced a bearing failure or any other kind of internal failure that puts debris into the crankcase, the oil pump should always be replaced.
Another item that should always be replaced (but often isn’t) is the pickup tube and screen. Pickups are difficult to clean and can hide debris that may damage a new pump or the the engine.
Pump Modifications
Performance engine builders will often rework the inlet and outlet ports of a stock oil pump housing to eliminate sharp edges that restrict oil flow. Using a die grinder to smooth and blend the sharp edges of the ports will enhance flow in and out of the pump. The clearance between the end of the gears and the pump housing cover should also be minimized to reduce pumping losses.
Some engine builders also install big block Chevy oil pumps on small block Chevy engines to increase oil flow. A stock big block Chevy oil pump has 12 teeth per gear versus 7 for the small block version, and flows about 10 percent more oil at the same rpm.
Something else to watch out for when installing a high volume oil pump in a small block Chevy V8 is the nylon retainer on the pump shaft. A better choice would be a pinned steel retainer to provide extra support between the intermediate shaft and pump shaft.
Care must also be used when tightening down the pump mounting bolts on small block and big block Chevy V8s because the pumps do not use a mounting gasket. The bolts should be torqued to 60-70 ft. lbs. so there are no leaks or sloppiness that would eventually cause the shaft to break.
Reducing Warranty Issues
The greatest oil pump in the world won’t keep an engine properly lubed if it is dry when the engine is first started, or it if sucks air because the oil level in the crankcase is low or the pickup screen is mounted too far above the floor of the oil pan.
The pickup tube should be installed so it is located no less than 3/8˝ above the floor of the oil pan (to allow good intake flow), and no more than 1/2˝ above the floor so it doesn’t run out of oil in a sharp turn.
The pump should also be filled with oil when it is mounted on the block to prime it and reduce the risk of a dry start. Do not use grease or assembly lube here. In the case of front mounted oil pumps inside the timing cover, the pump rotors can be coated with heavy oil such as 50W or even gear oil to keep the pump primed.
You should also attach a yellow or red tag on the engine warning the installer to prime the oil system with a pressurized oiler before cranking or attempting to start the engine. Oil tends to drain off bearing surfaces when an engine sits for more than a week or so without running. So if an engine has been sitting in a warehouse for a month or more before it is installed in a vehicle, you can bet the bearings are going to be dry unless they were precoated with a long-lived assembly lube.
On older engines with distributor driven oil pumps, the engine can be primed by using a drill to spin the oil pump shaft through the distributor hole. But on engines with no distributor or those with oil pumps inside the front cover, this isn’t possible. Feeding pressurized oil into the main oil gallery through the oil pressure sending unit fitting will route oil to all the critical areas inside the engine and eliminate the risk of scuffing the bearings when it is first started.
New Oil Pump Program
Vern Schumann of Schumann’s Sales & Service in Blue Grass, IA, said his company is launching a brand new oil pump program that will be sold under the Manley brand name. The new line will eventually include twelve of the most popular oil pumps, starting with four pumps in February. "Our goal is to create a quality program that will grow at its own rate, probably one pump a month," said Schumann.
"Our first applications will be for small block Chevy V8s and short deck 289/302 Windsor Ford V8s. The numbers are 55, 55HV (high volume), 55HV Racing, and 68."
Schumann said one of the advantages of launching an entirely new pump program from scratch is that he is not locked into any existing designs. Consequently, gear tolerances and relief pressures can be optimized for the aftermarket.
"Our 55 pump, for example, will have a kick out pressure of 60 psi, which is on the high end of the specifications. When engines are rebuilt, customers never complain about too much oil pressure. They typically complain about too little oil pressure. On small block Chevys with hot thin oil in the crankcase and a 200 degree thermostat, it’s common to see only about 10 to 15 psi of oil pressure at idle on the oil pressure gauge – which is not very reassuring. So we’re minimizing clearances to reduce pumping losses and to maximize oil flow at idle.
"Another problem with most relief valves is that the side of the valve as well as the end is exposed to oil pressure. This produces a sideways thrust that can cause the valve to hang up halfway in the bore. Our relief valves are redesigned so pressure is only applied to the end of the valve."
Schumann said improving machining accuracy and reducing tooth-to-tooth tolerances and gear-to-housing tolerances maximizes oil pressure at idle. "Something else you have to watch is the finish on the pedestal pads because this affects the end play of the pump gears. You don’t want any chatter marks on the pads because it will increase end play and cause a loss of pressure. Our pumps have .002˝ of end play and will stay that way because there are no chatter marks to wear away."
As for pricing, Schumann said his pumps will be competitively priced somewhere between the old DynaGear prices and those of the other major aftermarket suppliers.