All the moving parts are
subjected to wear and tear with time is a common phenomenon for automobile
engines. Worn out spare parts are replaced in scheduled maintenance services or as
unscheduled running repairs. Generally, the engine needs no repair over a stated period of
time other than lubrication. Servicing of engine internal parts and components
such as starter motor, alternator is called Engine Overhaul Repair.
How many kilometers can the engine be operated before engine overhaul repair ? It depends on the engine type and
capacity. 800 cc petrol engine may show 125,000 km while 1600 cc petrol engine
operate 400,000 km before engine overhaul repair. The practical experience shows that the distance operated before engine overhaul repair increases with the increasing number of
cylinders or the engine capacity.
When an engine reaches to
its engine overhaul repair condition, it may show symptoms such as high
engine oil consumption, excessive smoke, difficult starting, loss of engine
power and even over heating. Oil consumption is not the only factor to
determine the engine condition as even new engines may show excessive oil
consumption in cases such as oil rings being stuck in the piston ring
grove.
Engine wear mainly
occur on cylinder surface, piston rings, valve stems, valve seats
and valve guides. The excessive cylinder to ring clearance does not
prevent oil splashing into the combustion chamber and result in high engine oil
burn.
The
correct engineering practice to determine engine wear is the Engine
Compression Test which shows the ability of the cylinder to
maintain an air pressure for a certain period of time. Worn out engine is
unable to hold the air pressure as air passes through piston rings and valve
seats.
The main steps of engine overhaul repair are,
(1) Washing and cleaning engine exterior with high pressure air and water.
(2) Dismantling all engine components and units such as starter motor,
alternator, injector pump for repair.
(3) Inspecting
components such as cylinder bore, crankshaft, valves using precision
tools.
(4) Carrying
out cylinder re-boring, valve seat and crankshaft grinding and all the
repair work.
(5) Replacing worn out parts with new parts.
(6) Re-assembling the engine and inspection.
(6) Re-assembling the engine and inspection.
(7) Mounting
the engine on the engine test bench and running under different loads for different
time periods. Monitoring engine oil pressure, fuel consumption, battery
charging rate etc. are done at the test bench.
(8) Despatch
the engine for operation.
After the engine overhaul
repair, it is recommended to change engine oil and oil filter at 1000 km. Subsequent oil changes may continue as usual. High speed driving, running in low gear, hill climbing, continuous operation for
over one hour should be avoided during the running in period.