The strength of the BMW M4 Coupé is evident in every detail.
Lubrication tends to be neglected on older vehicles, especially those that are not regularly serviced.
Unlike such things as worn spark plugs, which bring on misfires or hard starting, or worn bearings, which knock or rumble, oil that is contaminated either by the ingress of fuel or full of minute particles shed from stressed parts of the engine, such as shell bearings, still continues to circulate and gives no audible clues to its condition.
Oil and filter changes at recommended intervals are essential money-savers.
Never economise on oil changes or oil quality.
Any solid material in the oil will act as an abrasive, wearing away crank journals, crank bearings, tappets and cam lobes. And when you think of the cost of renewing main bearings or big-ends on even the most basic four-cylinder engine, it makes sense to keep a written record of oil changes as well as regularly checking oil level.
Sludge may build up in an oil canister, so be sure to clean it out thoroughly when fitting a new filter. The oil pump itself plays an important role and the standard type, provided it is in good condition should normally be okay in the lower stages of tune.
However, an engine tuned more radically for higher performance might need a higher capacity pump, so it is as well to seek advice on gear clearances, etc. Remember that bearing clearances will be greater in an engine with a higher state of tune and flow potential could be compromised.
For an engine in semi-race tune a higher capacity pump is required.
Such a pump will have wider gears to ensure that sufficient oil is being delivered. This could also call for a stronger pump drive to cope with the extra loading.
Two main types of oil pump are in common use, namely the rotor and gear types. As there is no direct opening or path for oil to flow between the pump inlet and outlet, the pump is a positive displacement unit. Bearing clearances and metered holes restrict flow from the pump, resulting in pressure build-up.
A pressure regulator is incorporated in the pump. Excess pressure is sent to pump inlet or oil sump. This shows that engine oil pressure depends on regulator valve tension and restriction to flow on the pump outlet. It also follows that excessive bearing clearances will cause oil pressure to drop
Worn bearings cause a drop in oil pressure.
Most of us know that and when selling a car suffering from such a malady, some unscrupulous vendors use thicker oil to raise the pressure.
Mind you, a sticking regulator valve or damage regulator valve spring will also affect oil pressure. Pump wear that allows oil to bypass back to the inlet side will also cause a pressure drop.
Sometimes it is possible to increase pressure by using a stronger release valve spring or putting a suitable spacer under the existing spring. This was often done on four-cylinder Fords.
Oil analysis is a good pointer to the effectiveness of oil filtration and engine wear; it will also show dilution and sludge caused by excessive blow-by, neglected oil changes or even the use of unsuitable oil. Specialised laboratories will carry analysis for a small fee. - Star Motoring