Note: This chapter contains features that are unique to this series of engines. For general information on minor engine repairs, please refer to previous chapter.
One of the main problems with four-stroke internal combustion engines is that during the intake stroke, a sufficient amount of fuel-air mixture must enter the cylinders. As the engine speed increases, this problem becomes more serious, since the valve open time becomes shorter. This reduces the cylinder filling efficiency.
To combat this phenomenon, the valve diameter is made as large as possible: this is the only way to ensure the flow of a large amount of working mixture into the cylinders. However, it is impossible to increase the valve diameter indefinitely: it is limited by the combustion chamber diameter.
This is where the basic idea of four-valve-per-cylinder engines comes from: four valve plates fit better into a round combustion chamber and provide a larger intake cross-section than two valves in a combustion chamber of the same size.
Timing mechanism and oil pump drive for the M52 engine
1 - oil pump and its chain drive;
2 - crankshaft sprocket;
3 — primary chain tensioner shoe;
4 - hydraulic damper and tensioner spring;
5 - exhaust camshaft sprocket (double);
6 — intake camshaft sprocket.
Advantages of a 4-valve per cylinder engine
Four valves in each cylinder increase the area of the channels for passing the working mixture and exhaust gases. This in turn increases engine power and at the same time reduces fuel consumption. The specific fuel consumption of an engine with 4 valves per cylinder is approximately 8% less than that of an engine with 2 valves per cylinder.
The valves are smaller. This reduces the mass that the valve train has to move, which reduces its inertia. In addition, less rigid valve springs are required to close the valves,
Small valves cool better than large ones when in contact with the valve seats in the closed state. This increases their heat resistance. Due to the change in the combustion chamber proportions, engines with 4 valves per cylinder have greater detonation resistance. Compression in them increases by 1-5 points.
In an engine with 4 valves per cylinder, the spark plug can be installed in the most suitable place for it - in the center of the combustion chamber.
[Information taken from this resource: «BMWMan.ru»]