What is an Oil Pump?
The oil pump in an internal combustion engine is usually a gear type driven by the camshaft or crankshaft, or a rotor type. Oil pressure varies quite a bit during operation, with lower temperature and higher RPM’s increasing pressure to a maximum of about 4 bar.
To ensure that the oil pressure does not exceed the rated maximum, a spring-loaded pressure relief valve routes oil back to its source once pressure exceeds a preset limit. The oil pump usually sucks the oil out of the engine’s oil pan through a wire mesh strainer and pumps the oil through an oil filter before it goes to the bearings.
At 3,000 rpm, the pistons inside your engine are moving up and down violently, the crankshaft is spinning swiftly, and the rocker arms are rapidly doing the two-step with each respective valve. But whether your engine is just idling in drive or at full-throttle, it takes a good lubrication system to keep everything from turning into molten metal.
To prevent this unsavoury transformation, oil is directed to all of the metal contacting surfaces by a full-pressure lubrication system comprised of an oil pan, an oil pump, several quarts of oil, and a series of passages inside your engine.
A stock Chevrolet V-8 engine uses a wet-sump system (oil reservoir located directly below the crankshaft) with internal passages within the cylinder block, crankshaft, and openings in the cylinder heads. A 1/2-inch diameter oil pump inlet on small-blocks (5/8-inch diameter on big-blocks) with an ample suction screen submerged in engine oil provides free-flowing oil to the pump, which is driven by the camshaft.
The oil that is supplied to the pump travels through a full-flow oil filter into a 1/2-inch main gallery on a small-block (9/16-inch on a big-block) that is located above the camshaft. From there, the lube travels through a hole to a groove near the rear side of the rear cam bearing (’57-and-later V-8s) and is where the lifters and rear main are oiled. Additionally, all four front cam bearings have grooves that pass to each particular main bearing. Through small holes in the upper main bearings, oil passes down into the crankshafts main journals where it travels to the rod journals.
While all of this is occurring, the crankshaft is spinning and each connecting rod is throwing oil onto the respective cylinders to lube the moving pistons and rings and help seal combustion. At the top of the engine, oil has travelled from each lifter and up through the hollow pushrods, over the rocker arms, and down onto the springs and valve stems where it helps to lube the valve stems as they move in the valve guides. To keep the pressure from getting too high at the oil pump, a relief valve circulates the oil back to the inlet side of the pump when pressure surpasses the relief spring’s limit.
High-performance engines place increased bearing loads on the oiling system (especially during higher rpm), and if it’s not up to the task, it can cause very premature engine failure.
To combat this, most aftermarket high-performance pumps provide a 20-30 percent increase in both volume and pressure. For most applications, you’ll want a good pump that delivers in the neighbourhood of 55-65 psi or about 10 psi per every 1,000 rpm; anything more may just add air into the system or labour the engine with the task of turning an oil pump that makes excessive pressure. If you doubt that an oil pump takes power to turn, watch what happens to a drill motor during the initial phase of oil pump priming.
Most aftermarket pumps come with a new pickup installed and brazed into position. If yours does not, you should braze the pickup into the pump body, positioned about 1/4-inch (0.250-inch) above the bottom of the pan. Before brazing it to the pump cover, remove the pin, spring, and relief piston from the cover so that the heat won’t damage them.
Put the pump securely in a soft-jawed vice and tap the pickup into the oil pump with a homemade tool or one from a specialty tool company. To measure the pickup-to- pan clearance, place a small piece of clay between the pickup and bottom of the pan and install the oil pan gasket in a mock-up (without adding sealant).
But before you install a new oil pump onto the engine, it’s always a good idea to double-check the end clearance of the pump gears beforehand. For most small- and big-block Chevys, the pump gear’s end clearance should be very close to 0.0025-inch, but it’s always best to first check with the pump manufacturer for the spec. To check this dimension, disassemble the pump and de-burr both gears with a small file.
Then, reinstall both gears and measure the endplay (from the top of the gears to the top of the pump housing) using a depth micrometer or a feeler gauge. If you install a pump with a measurement that exceeds the 0.0025-inch spec, then the pump will not prime as easily and/or perform as well.
If the endplay is greater than this, it can be corrected by sanding the pump body with a piece of solvent-wet 220 wet/dry sandpaper placed on a hard and very flat surface, such as a thick piece of glass. To correct clearance that measures too small, sand the gears on the top end in the same manner as the pump body.
In either case, remember to wash everything in solvent and then blow-dry it (rags will leave lint) before reassembly. To install the pump on the rear main cap, first be certain that the hole in the pump aligns with the hole in the main cap. This may require chamfering the holes so that they line up with each other.
Supply and Demand
Look inside of a stock or high-performance pan and you’ll see baffles there to keep the oil pickup submerged during cornering, accelerating, or stopping. For high-performance pans, the baffling is typically far more elaborate and designed to better withstand the forces of extreme-duty operation. Critical to a good oil pan’s design is also how well it allows gravity drain-back into the sump.
For many high-performance applications, the size of the sump may be larger than stock. For most street-driven cars, chassis and ground clearance requirements dictate the depth (and width) of the oil pan’s sump area, so for many applications, wide sump pans are available.
At engine speeds above 6,000 rpm, the moving oil can whip the crankshaft and cost power. This phenomenon is called windage and is minimized by installing either a windage tray or a semi-circular screen to move the oil away from the spinning crankshaft without splashing back on the throws.
Conclusion Building the best oiling system for your engine depends on planning, budgeting, and how you’ll use your vehicle. If you’re simply building for moderate street and limited track use, there are many high-performance oil pumps and oil pans that will increase volume and pressure without destroying your budget.
For very high-performance use, there are a multitude of oil pans, pumps, windage trays, and hardware to almost eliminate the possibility of encountering an oiling problem. The key is choosing the right parts, installing them correctly, and operating the engine the way it was designed.
