An internal combustion engine develops the most power at a certain speed; this is called the rated speed. Increasing the engine speed above the nominal speed does not result in an increase in power. The maximum permissible speed depends on the type of engine: from 4500 rpm (diesel) up to 6500 rpm (16 valve engine). In doing so, it is about «operating speed», which is not dangerous for long-term operation of the engine in this mode. An increase in the number of revolutions above the indicated values is adversely affects the condition of the engine. At the same time, the engine starts to make a lot of noise; this is due to vibrations of the crankshaft in the area of the bearings and vibrations of the valves. On a 16-valve engine, the operation of hydraulic lifters is disrupted.
If the vibrations are too strong, the valve springs or valve levers may break; in addition, the push rod may be damaged (C-engine) and valve lifter, which will damage the valve. The latter is the worst option, since the valve can get under the moving piston, which will lead to engine failure. With a broken valve lever, valve lifter or broken push rod (C-engine) only the corresponding valve and cylinder does not work. This will become noticeable by a decrease in engine power. To know the permissible engine speed, some Renault 19 modifications are factory equipped with a tachometer. This device has some advance - in the upper part of the scale up to 5%. Thus, 6000 rpm on the tachometer actually corresponds to only 5700 rpm.