Engine Lubrication: Description and Operation

Lubrication System

the lubrication system is the full flow filtration pressure feed type. the oil fill process at the factory allows for a tolerance of 4mm above to 4mm below the maximum mark on the oil level dipstick. the oil level will depend on the oil temperature and length of time from the last engine switch off.

Oil Circuit
Oil is drawn up through the oil strainer to the oil pump, which is located at the front of the engine: the oil pump delivers oil under pressure through the full flow oil filter to the main oil gallery.
the main oil gallery runs the full length of the engine block and delivers oil to the main bearings. Diagonal drillings in the crankshaft webs deliver oil to the connecting rod bearings. the cylinder bores and connecting rod small end are splash lubricated from directed slots on the connecting rod thrust collar.

A key way locates the crankshaft gear (23 Teeth). the camshaft timing gear (46 Teeth) is located by a key way and is retained by a central bolt. the camshaft gear is driven by a roller timing chain.
the main oil gallery also supplies oil to the cylinder head assembly via a vertical hole on the exhaust side of the cylinder block between bores two and three. the cylinder head gasket incorporates an oil restrictor to ensure that oil volume to the crankshaft is maintained and oil volume to the cylinder head is reduced.

Upper engine lubrication is provided by one main feed to the number three camshaft bearing cap. Oil is then routed through the rocker shafts to the remaining camshaft bearing caps and rocker arms/hydraulic lifters. Oil returning to the sump pan from the pressurized components supplies lubrication to the valve stems.


Piston Cooling - MINI COOPER S Only
the MINI COOPER S incorporates oil "squirt" jets to assist in the cooling of the piston crown. the four jets are located in the cylinder block next to the main oil gallery. Oil spray is controlled by a ball and spring. These allow oil flow only when the oil pressure exceeds 2 bar. the position of each jet is critical to the effectiveness of the cooling.


Oil Pump
the oil pump and pressure relief valve are located on the front cover (internally) and are secured by 10 bolts. They are both manufactured from aluminum.
the oil pump consists of two gears. the internal gear is driven directly from two flats on the crankshaft nose and is in permanent mesh with the outer gear.
the eccentric rotation of the gears creates a low pressure at the inlet suction crescent end of the pump and draws in oil. As the gearwheel rotates, oil will be compressed between the gears and discharged at the outlet port end of the crescent at a high pressure.

Oil Pressure Regulator
the oil pressure relief valve is installed in the oil pump housing. the valve consists of a spring, retaining cap, circlip and hollow plunger with radial holes.
It a blockage or restriction occurs and the oil pressure is sufficient to overcome the spring tension, the plunger will be forced back, exposing the radial holes and oil will return to the low pressure side of the pump.


Oil Filter Housing



the oil filter housing is located adjacent to the exhaust manifold and is externally mounted by three bolts.
the housing incorporates a spring-loaded drain back function, allowing oil to return to the oil pan. the drain back function is activated as the oil filter top housing is unscrewed.
the oil filter housing also retains a bypass valve for the full flow oil filter and an oil pressure switch. the oil filter is a disposable paper element and is retained in the upper section of the aluminum housing.