5.1.12. Diagnostics of technical condition of the engine and its possible malfunctions

Technical condition of the engine in use constantly changes. In the period of a running in (about 2000 km) on a measure extra earnings of the rubbing surfaces decrease losses by friction, engine capacity increases, fuel consumption decreases, oil waste decreases. Further there comes the period at which technical condition practically changes a little. In process of wear of details the break of gases through piston rings increases, the compression in cylinders falls, leak of oil through gaps in connections increases and pressure in system falls. Therefore, engine capacity gradually decreases, fuel consumption increases, the oil consumption increases.
Definition of technical condition of the engine is very important for timely recovery repair. It will prolong total period of service of the engine and the emergency exit of the engine out of operation will warn.
The condition of the engine is estimated on indicators of devices (temperature of cooling liquid and pressure of oil), kind of work of the engine on various modes (uniformity, to noise qualities), in compression size in cylinders of the engine, reaction of the car to fuel supply change by an accelerator pedal.
Falling of engine capacity is shown in decrease in dynamic qualities of the car, in deterioration in acceleration performance. The car inertly accelerates, hardly overcomes rise (it is necessary to include prematurely lowering transfer), does not gather the maximum speed. It must be kept in mind that the specified signs can be also a consequence of violation of adjustment of mechanisms of a running gear of the car.
The way of free swing (выбег) of the serviceable car, with full loading, moving with a speed of 50 km/h, has to be not less than 550 m. Such test is carried out to windless weather on the dry horizontal section of the highway with an asphalt or concrete covering.
Fuel consumption (operational) depends not only on technical condition of the engine, but also (at working order of a running gear of the car) on road conditions, loading, driving methods therefore operational fuel consumption is not an objective indicator of technical condition of the engine.
Technical condition of the engine (at serviceability of other mechanisms of the car) decides by control fuel consumption at the movement of completely loaded car on the horizontal section of the highway on an asphalt or concrete covering with a speed of 60 km/h. Test is carried out on the site 4 — 5 km long in two opposite directions. The control expense for the rolled car should not exceed 11 l on 100 km. When determining a control consumption of gasoline use a separate measured tank.
Check of a compression (pressure) in cylinders at the end of a step of compression is made kompressometry. Before measurement it is necessary to check correctness of thermal gaps in valves and if necessary to adjust. The compression in cylinders is measured on the engine which is warmed up to 70 — 85 °C at completely open butterfly valve of the carburetor and the turned-out candles, the carburetor at the same time has to be without fuel.
The rubber tip of a kompressometr is inserted into an opening of a candle of the first cylinder, providing consolidation on an opening edge, and the bent shaft of the engine is scrolled by a starter until pressure in the cylinder does not cease to increase (but no more than 10 — 15 sec.). The rechargeable battery has to be serviceable and completely loaded.
The compression in cylinders for the engine 4026 less than 850 kPa (8,5 kgfs/cm2) and for the engine 4025 less than 800 kPa (8 kgfs/cm2) testifies to wear or malfunction of piston rings or to leakage of landing of valves. To establish a true cause of defect, it is necessary to fill in through a candle opening in each cylinder 20 — 30 cm3 of the oil applied to the engine and again to check a compression. Increase in a compression indicates malfunction (wear) of rings or the cylinder; if value of a compression did not increase, then, therefore, tightness of landing of valves is broken.
The oil consumption on waste is controlled by measurement of amount of the oil added to the tag "П" of the index of level for a certain run. Gradually, in process of increase in wear of details of the engine, the consumption of oil increases. If the oil consumption on waste exceeds 0,25 l on 100 km, then the engine is subject to repair.
Oil pressure in system is checked by the control manometer which joins an oil filter instead of the oil pressure sensor (a carving in the filter 1/4 conic). Oil pressure less than 100 kPa (1 kgf/cm2) on the heated-up engine with an average frequency of rotation and less than 50 kPa (0,5 kgfs/cm2) with a small frequency of idling testifies to malfunctions in the lubrication system or excessive wear of bearings cranked or the camshaft. Such engine is subject to repair.
Noisiness of operation of the engine is checked by listening of its work idling with various frequency of rotation of a bent shaft. The engine has to be heated-up up to the temperature of 70 — 85 °C.
Without application of a stethoscope listen to operation of the gas-distributing mechanism: valves — with a frequency of rotation of 600 — 1200 min.-1, pushers — with a frequency of rotation of 1000 — 1500 min.-1, camshaft gear wheels — with a frequency of rotation of 1000 — 2000 min.-1. By means of a stethoscope listen to work of piston group, conrod and radical bearings at sharp short-term increase in frequency rotation of a bent shaft up to 2500 min.-1.
The knock and tinkling sound of pistons, piston rings, the knock of conrod bearings listened by a stethoscope are not allowed; the allocated knock of piston fingers, radical bearings, knock or sharp noise of high-pitch tone of distributive gear wheels, the sharp allocated knock of valves and pushers, the sharp knock and noise of high-pitch tone of gear wheels of the oil pump and its drive, noise of high-pitch tone and peep of a krylchatka and the bearing of the pump of cooling liquid listened without stethoscope. Are allowed the uniform knock of valves and pushers merging in the general noise; periodic knock of valves and pushers at normal gaps in the valvate mechanism; the allocated knock of valves and pushers disappearing or appearing at sharp change of frequency of rotation of a bent shaft of the engine; equal unsharp noise of gear wheels of the drive of the camshaft and the noise of gear wheels of the oil pump and its drive which is not allocated from the general background.
During operation of the car there can be various malfunctions of the engine for which elimination are not required deliveries of the car in special repair shop. On operation of the engine at sufficient skill it is possible to judge its technical condition. The increased gaps in interfaces, casual breakages and weakening of fasteners can be aurally revealed. Having found in use any malfunction in operation of the engine, it is necessary not to hurry to disassemble the engine, and to try to establish a cause of defect before dismantling.
Start dismantling of the engine, having convinced of the valid need of this operation. Even partial dismantling of the engine breaks, as a rule, consolidations, to extra earnings of the interfaced details and increases their wear at the subsequent operation.