On its bottom, the sump contains an oil intake covered by a mesh filter which is connected to an oil pump then to an oil filter outside the crankcase, from there it is diverted to the crankshaft main bearings and valve train.
The crankcase contains at least one oil gallery (a conduit inside a crankcase wall) to which oil is introduced from the oil filter.
The main bearings contain a groove through all or half its circumference; the oil enters to these grooves from channels connected to the oil gallery.The crankshaft has drillings which take oil from these grooves and deliver it to the big end bearings.
The connecting rod may have a nozzle to throw an oil jet to the cylinder and bottom of the piston.
That nozzle is in movement relative to the cylinder it lubricates, but always pointed towards it or the corresponding piston. Typically a forced lubrication systems have a lubricant flow higher than what is required to lubricate satisfactorily, in order to assist with cooling.
The necessary high voltage, typically 10,000 volts, is supplied by an induction coil or transformer.
With either system, a mechanical or electrical control system provides a carefully timed high-voltage to the proper cylinder.
This spark, via the spark plug, ignites the air-fuel mixture in the engine's cylinders. While gasoline internal combustion engines are much easier to start in cold weather than diesel engines, they can still have cold weather starting problems under extreme conditions.
In some parts of the world the oil was actually drained and heated over night and returned to the engine for cold starts.
In 2-stroke crankcase scavenged engines, the interior of the crankcase, and therefore the crankshaft, connecting rod and bottom of the pistons are sprayed by the 2-stroke oil in the air-fuel-oil mixture which is then burned along with the fuel.
The valve train may be contained in a compartment flooded with lubricant so that no oil pump is required. In a splash lubrication system no oil pump is used.Instead the crankshaft dips into the oil in the sump and due to its high speed, it splashes the crankshaft, connecting rods and bottom of the pistons.
Splash lubrication is common for small 4-stroke engines. In a forced (also called pressurized) lubrication system, lubrication is accomplished in a closed loop which carries motor oil to the surfaces serviced by the system and then returns the oil to a reservoir.The auxiliary equipment of an engine is typically not serviced by this loop; for instance, an alternator may use ball bearings sealed with its lubricant.
The reservoir for the oil is usually the sump, and when this is the case, it is called a wet sump system.
When there is a different oil reservoir the crankcase still catches it, but it is continuously drained by a dedicated pump; this is called a dry sump system.Źródło: https://en.wikipedia.org/wiki/Internal_combustion_engine.