Melling Sweats The Details On Wet Sump Oil Pump Technology Part 1

Over the past few issues we’ve dug deep into Melling’s billet aluminum oil pumps. They clearly offer all sorts of technical advantages. With this segment, we’ll take a few final looks at the Melling pumps, but as mentioned last time around, we also have a series of oil pump install tech tips (courtesy of Melling ) we’d like to share. They’re important and offer a wealth of info for any engine builder. To begin, let’s look at the advantages and myths of high volume oil pumps (directly from the folks at Melling): “Most stock automobile engines are designed to operate from idle to 4,500 RPM. The original volume and pressure oil pump will work fine in this type of application. As the demands of the engine increase so does the demand upon the oiling system and pump. “The oil pump’s most difficult task is to supply oil to the connecting rod bearing that is the furthest from the pump. To reach this bearing, the oil travels from three to four feet, turns numerous square corners through small holes in the crankshaft to the rod bearing. The rod bearing doesn’t help matters. It is travelling in a circle which means centrifugal force is pulling oil out of the bearing. “A 350 Chevy has a 3.4811-inch stroke and a 2.111-inch rod journal. At 1,000 RPM, the outer edge is travelling at 16.6 MPH and 74.7 MPH at 4,500 RPM. If we take this engine to 6,500 RPM the outer edge is up to 107.9 MPH and at 8,500 RPM, it is 141.1 MPH. Now imagine driving a car around a curve at those speeds and you can feel the centrifugal force. Now imagine doing it around a circle with a 5.581-inch diameter. “The size of the gears or rotors determine the amount of oil a pump can move at any given RPM. Resistance to this movement creates the pressure. If a pump is not large enough to meet the demands of the engine, there will not be any pressure. Of if the demands of the engine are increased beyond the pump capability, there will be a loss of oil pressure. This is where high volume pumps come in – they take care of increased demands of the engine. “Now consider what a high volume pump will not do: “It will not replace a rebuild in a worn-out engine. It may increase pressure, but the engine is still worn out. “It will not pump the oil pan dry. Both solid and hydraulic lifters have metering valves to limit flow of the oil to the top of the engine. If a sump is pumped dry, it is because the holes that drain oil back to the pan are plugged. If the high volume pump is also a higher pressure model, there will be a slight increase in flow to the top. “It will not wear out distributor gears. The load on the gear is directly related to the resistance to flow. Oil pressure is the measure of the resistance to flow. For example, the Ford 427 FE “side oiler” used a pump with the relief valve set at 125 PSI and used a standard distributor gear. Distributor gear failures are usually caused by a worn gear on a new cam gear and/or worn bearings allowing misalignment (aside from a mismatch in cam and distributor gear materials.” Next up are a series of installation tech tips from Melling: “The Melling small block billet performance pumps will provide oil pressure between 60 and 80 PSI. But engine clearances may require changing the pressure relief spring. To increase the oil pressure by 10 PSI, install the dark orange spring. To decrease the pressure by 10 PSI, install the pink spring. To do this, remove the valve plug and spring, install either of the optional springs and torque the valve plug to 10 foot-pounds minimum. “Before final installation, be sure to test fit the oil pump on the block to verify crankshaft and connecting rod clearance. Check the oil pump drive shaft clearance to the main cap and engine block. Also check to verify proper clearance from the stand-offs at the bottom of the oil pump to the bottom of the oil pan of ¼-inch to 3/8-inch. The stand-offs assure that the oil supply to the pump will not be cut-off in the event the pan comes in contact with the oil pump. “Before installing the pump, submerge the pump pickup in oil and rotate the driveshaft by hand. Rotate the driveshaft in a clockwise direction until oil is pumped out the top of the pump. “Before starting a newly assembled engine, the lubrication system requires priming. Us an oil primer shaft or the modified end of an old distributor connected to an electric drill to spin the oil pump driveshaft in a clockwise direction. This will assure that pressurized oil will be readily available during initial start-up.” ### In the end, the folks from Melling have come up with a major improvement for both small block Chevy and big block Chevy wet sump applications. This has been accomplished without increasing the size of the pump, which in turn would create a need for a new oil pan and/or windage tray configuration. Essentially, the new pumps from Melling prove to be direct bolt in swaps for more conventional oil pumps. Melling really does sweat the details when it comes to wet sump oil pump technology. For a closer, check out the accompanying photos. Click Here to Begin Slideshow

Wet Sump Oil Pump Part 1

There are a lot of choices today when it comes to oil pumps. The aftermarket is full of options (no secret we’re sure). And yes, there have been countless innovations over the years. We’ll get to a couple of really good ones later, but first, ponder why you really should sweat the details when it comes to wet sump oil pumps:

Let’s start at the beginning. The cam, main and rod bearings inside an engine are very simple devices. The most common arrangement we typically see consist of flat, coated inserts. Bearing inserts have zero moving parts (in contrast to a ball bearing or a roller-type bearing you might find in a two stroke engine). Automotive bearings simply rely upon hydro-dynamic principles.

What this means is the crankshaft journals (or the camshaft journals for that matter) do not actually rotate directly on the bearing surfaces. Instead, they rotate on a wedge of pressurized oil. In order to create that “wedge”, oil must first be pumped into the bearing with sufficient force and sufficient quantity to physically lift the journal off the bearing surface. As the crankshaft is rotating, that hydro-dynamic wedge of oil that was created, follows the journal. This prevents the metal journal surface from touching the bearing surface. Basically, the crank and cam journals spin on a cushion of oil.

Using a conventional Chevy wet sump oil system as the example, oil is first drawn through the pickup screen into the oil pump. Here, a pair of gears inside the pump pressurize the oil and then it goes through a gallery within the cylinder block that delivers it to the oil filter. Oil is forced through a filtration medium (paper and/or screen) and then it exits into the main oil gallery. At this point, oil is delivered to the main journals along with the cam bearings. Oil flows through a series of drilled passages in the crankshaft and is directed toward the rod bearings. Oil from the main gallery also moves through the lifter galleries where it’s distributed to the valve lifters. In a typical Chevy application oil that is pumped into the lifters is discharged through hollow pushrods. In turn, this pressurized oil lubricates the pushrod tips along with the rocker arms. Oil pumped to the top of the engine than simply runs back over the valve spring as well as the valve stem and eventually drains back into the sump. This arrangement provides a cooling effect for the springs and obviously provides lubrication for the valve stems and valve guides.

Those aren’t the only pieces lubricated and cooled by oil spray or by way of splash lubrication. Many engine components are lubricated and cooled by oil splash or spray. For example, oil flung off the spinning crank and cam assembly is used to lubricate the cylinder walls, pistons, piston pins, camshaft lobes, distributor gear and timing chain. This oil spray is important and we’ll get it a bit further down the page.

Oil pressure in the range of 30 or 40 pounds per square inch (PSI) is often sufficient in order to maintain proper engine lubrication in a passenger car engine. In contrast, a high performance or race engine application places considerably higher demands and loads on reciprocating components. Increase the operating range (typically past 7,000 RPM in many high performance applications), and the need to increase oil pressure also increases. More pressure is necessary to maintain the separation between the cam and crank journals and the bearings. It’s for this reason one often sees oil pressure figures of 50 to 60 PSI and beyond in race applications. Of course, the design and type of the engine also dictates oil pressure requirements. There are some restricted class cars (for example, some NHRA Stock and some NHRA Super Stock classes) where reduced oil pressure coupled with very thin oil and/or the reduction of oil within the sump is used to increase horsepower. This of course, isn’t without consequences. Ultimately, durability suffers. But for the most part, the oil flow rate in high performance applications typically ranges from 8 to 12 gallons per minute. The oil pump you chose must be capable of maintaining pressure at this flow rate in order to avoid bearing to journal contact. Once a bearing and a journal come in contact with each other, we all know it’s pretty much over and you’re faced with the dismal prospect of engine failure.

Fair enough. There are ways to resolve this. But you can go too far and we’ll get into it in the next issue. Watch for it. And the meantime, check out the following examples of new oil pump technology from the folks at Melling .

Wet Sump Oil Pump Part 1 Slide 2

(Photo Credit: Chevrolet)
This vintage Chevrolet drawing shows a portion of the path oil must tank when lubricating a small block.

Wet Sump Oil Pump Part 1 Slide 3

Melling manufactures a number of different oil pumps – replacement examples, high performance examples and top of the heap billet examples.

Wet Sump Oil Pump Part 1 Slide 4

You’ll note these pumps (big block on the right; small block on the left) aren’t massive in size. This allows them to fit in locations previously occupied by a conventional style iron body pump.

Wet Sump Oil Pump Part 1 Slide 5

The bodies and covers (pickups) on both oil pump are machined from 6061-T6 billet aluminum and then hard-coat anodized for long service life.

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