Melling Sweats The Details On Wet Sump Oil Pump Technology Part 4

When you examine the pickup on either pump, you can see the screen is a stainless-steel mesh. It’s held in place by way of a healthy c-clip. The text offers more info.

Wet Sump Oil Pump 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.

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Wet Sump Oil Pump Part 4

When you examine the pickup on either pump, you can see the screen is a stainless-steel mesh. It’s held in place by way of a healthy c-clip. The text offers more info.

Wet Sump Oil Pump Part 4

After checking out the gears on both pumps, you can see the big block makes use of a conventional gear layout while the small block setup is asymmetrical. The Shark Tooth profile allows for smoother operation in the mouse motor application.

Wet Sump Oil Pump Part 4

The respective pump drive shaft lengths have increased. This patented design provides for additional support within the cover. By increasing the support, Melling was able to eliminate shaft deflection. In turn, this allows the gears to run true at high RPM levels.

Wet Sump Oil Pump Part 4

The pump drive shaft incorporates a beefy pinned collar on the pump end. Internally, there’s a machined rib that snaps into the groove on the pump shaft.

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