Oil pump (internal combustion engine)

As well as its primary purpose for lubrication, pressurized oil is increasingly used as a hydraulic fluid to power small actuators.

To avoid the need for priming, the pump is always mounted low-down, either submerged or around the level of the oil in the sump.

A short pick-up pipe with a simple wire-mesh strainer reaches to the bottom of the sump.

Placing the oil pump low-down uses a near-vertical drive shaft, driven by helical skew gears from the camshaft.

When the twin overhead cam engine was developed, the previous oil pump arrangement was retained and the camshaft became a shortened stub shaft.

[4] Small engines, or scooters may have internal gear pumps mounted directly on their crankshaft.

Additional separate belts are sometimes used where dry sump pumps have been added to engines during tuning.

Properly lubricating an engine not only reduces friction between moving parts but is also the main method by which heat is removed from pistons, bearings, and shafts.

All pump pressure does is "fill in the hole" and refresh the oil in the annular space faster than the leak expels it.

This is why low-speed engines have relatively large journals, with only modest pump size and pressure.

Low pressure indicates that leakage from the bearings is higher than the pump's delivery rate.

Despite the frequent comparison to hydraulic engineering theory, this is not a "closed system" in which oil pressure is balanced and identical everywhere.

All engines are "open systems", because the oil returns to the pan by a series of controlled leaks.

[7] Too much oil pressure can create unnecessary work for the engine and even add air into the system.

This is why there is a significant difference between cold & hot oil, high & low RPM, &c., but it's typically not a problem with stock engines because of the spring-loaded pressure relief valve mentioned above.

The first thing to fail will be cam carrier bearings if the vehicle is OHC as this is fed through a restrictor and low pressure will starve the top of the engine of lubrication.

For instance, .001 of an inch worn off of the engine's main bearings can cause up to a 20% loss in oil pressure.

The holes in the screen are so big (relative to debris) because at low temperatures and slow engine speed the oil is very viscous and needs large openings to flow freely.

The piston rings serve to seal the combustion chamber, as well as remove oil from the internal walls of the cylinder.

Dry sumps also allow for more power because they reduce the amount of windage, oil sloshing up into the rotating assembly, and the vacuum from the scavenge pump improves ring seal.

Disadvantages of dry sumps are increased weight, additional parts, and more chances for leaks and problems to occur.