Attention: This chapter contains special features that are unique to this engine series. For general information on minor engine repairs, 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 air-fuel mixture must enter the cylinders. As the speed increases, this problem becomes more serious, as the open time of the valves becomes shorter. This reduces the filling factor of the cylinders.
To combat this phenomenon, they try to make the diameter of the valves as large as possible: this is the only way to ensure the flow of a large amount of the working mixture into the cylinders. However, it is impossible to increase the diameter of the valves to infinity: it is limited by the diameter of the combustion chamber.
This is where the basic idea of four valves per cylinder engines comes from: four valve heads fit better in a round combustion chamber and provide a larger intake area than two valves in a combustion chamber of the same size.
The drive of the gas distribution mechanism and the oil pump of the M52 engine
1 - oil pump and its chain drive;
2 - crankshaft sprocket;
3 - shoe tensioner primary chain;
4 - hydraulic damper and tensioner spring;
5 - exhaust camshaft sprocket (double);
6 - intake camshaft sprocket.
Advantages of an engine with 4 valves per cylinder
Four valves in each cylinder increase the area of 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 about 8% less than that of an engine with 2 valves per cylinder.
Smaller valves. This reduces the mass that the timing gear has to move, thereby reducing its inertia. In addition, less stiff valve springs are required to close the valves,
Small valves cool better when they contact the valve seats when closed than large valves. This increases their heat resistance. Due to the change in the proportions of the combustion chamber, engines with 4 valves per cylinder have a greater knock 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.