Engine Maintenance

Engine Maintenance

A sound engine should develop full power, run steadily under full-load and no-load conditions, without overheating, smok-ing, oil or coolant leakage. Some troubles can be identified by their symptoms without disassembling the engine.

The symptoms indicative of some troubles with the crank gear include foreign noise and knocks, loss of power, excessive oil and fuel consumption, smoky exhaust.

Noise and knocks in the engine are caused by the wear of its basic parts leading to excessive clearance between its mating parts.

If the piston and cylinder are worn and the clearance between them is exeessive, a clear metallic knocking appears, which is most vivid when the engine runs cold. A sharp metallic knocking at all speeds indicates an increased clearance between the piston pin and the connecting rod bush. If the knocking grows when the engine is sharply throttled up, the main or crankpin bearing shells are worn, the duller knocks symptomizing the wear of the main bearings. Sharp continuous knocking in the engine accompanied by the oil pressure drop is an evidence of melting out of bearings. The engine knocks can be listened to with the use of stethoscope.

Loss of engine power stems from the drop of compression which may occur when the cylinder block head nuts are tightened nonuniformly or insufficiently, or the head gasket is damaged, the piston rings are stuck in the grooves owing to carbon or lacquer deposit; the rings are worn, broken or lost their resilience; the cylinders are worn.

The compression can be checked with a compression gauge or by hand. To check the compression by hand, drive out the spark plugs from all the cylinders but the one being checked. While rotating the crank, estimate the compression by the resistance to the rotation. The compression in other cylinders is checked in a similar way.

To check the compression with a compression gauge, warm up the engine, drive out the spark plugs, fully open the throttle and choke valves. Install a rubber nipple of the, compression gauge into the plug hole, turn the crankshaft 8 or 10 times and check the gauge reading. After the crankshaft is turned, the pressure in the god cylinder should be 7. 0-7. 8 kgf/cm² (0 7-0. 78MPa). This procedure should be used to check the compression consecutively in all the cylinders of the engine.

Excessive fuel and oil consumption and smoky gray exhaust (the oil level in the crankcase being normal) are usually attributed to the sticking or wear of the piston rings. Sticking can be remedied without disassembling the engine; for this purpose, mix equal parts of denatured alcohol and kerosene and pour 20g of the mixture into each cylinder through the spark plug hole, leaving it there overnight. In the morning start the engine, run it for 10 to 15 minutes, shut down and change the oil.

Carbonization of the engine, i.e. deposition of carbon on the piston crowns and combustion chambers, impairs heat transfer and leads to overheating, loss of power and excessive fuel consumption. To remove the carbon deposit, drain the coolant, remove the units mounted on the cylinder head, undo the nuts and detach the cylinder head carefully so as not to damage the gasket. If the gasket has stuck to the head or block, separate it with a blunt knife or a wide and thin strip of metal.

Remove the carbon deposit with scrapers made of wood or soft metal to avoid damaging the piston crowns or combustion chamber walls. In so doing, cover the adjacent cylinders with clean rags. The carbon deposit goes off easier after softening by applying kerosene-soaked rags.

When installing the cylinder block head gasket, wipe it with powdered graphite.

Cracks in the walls of the cylinder block and head may result from freezing of water or filling cold water into a hot engine.

The main troubles characteristic of the valve gear are improper seating or incomplete opening of the valves.

Improper seating is symptomized by poor compression, popping in the inlet and exhaust manifolds and loss of power. Improper, seating may be caused by carbon deposit on the valves and seats, pitting of their working surfaces, warping of the valves heads, broken valve spring, sticking of the valves in the guides, absence of clearance between the valve stem and the rocker.

Incomplete opening of the valves is characterized by knocking in the engine and loss of power. This derangement stems from excessive clearance between the valve stem and the rocker.

The valve gear troubles also include wear of the crankshaft gears, tappets, guides, excessive end play of the camshaft, wear of rocker bushing and fulcrums.

To adjust the clearance between the valve stem and the rocker, remove the valve cover, first detaching all the parts mounted on it; shift the piston to TDC on the compression stroke so that the valves are closed; check the clearance and adjust it, if necessary, as follows: undo the lock-nut on the rocker adjusting screw, set the required clearance by rotating the adjusting screw, tighten the locknut holding the screw with the screwdriver and recheck the clearance.