Spektoruk. S.A
Kostanay
State University, Kazakhstan
Finding malfunctions in crank mechanism and ways of its repair
A
crank mechanism of an engine is used to convert linear motion of the pistons to
rotary motion of the crankshaft. It consists of a cylinder block, one common or
several individual cylinder heads, pistons with rings and piston pins,
connecting rods, crankshaft with bearings, sump and flywheel. Reliable using of
the crank mechanism during car exploiting provides timely care for it and use
of lubrication oils which are recommended by manufacturer.
Causes
of malfunctions in crank mechanism.
Faults
in the crank mechanism are the result of wear of piston rings, pistons and
cylinder liners, main and connecting rod bearings and crankshaft necks, piston
pins, piston holes in bosses or bronze bushings of upper crosshead, damaged
cylinder head gasket or loose heads block.
Signs
of these faults are characteristic knocks, which are easily listened using
devices such as a stethoscope. By the nature of knocking or noise of the engine
at a certain place determined by the type of fault.
To
determine by knock or noise the cause of its appearance, it is necessary to
know a nature of knocks at various faults. For example, the sound of the
pistons are characterized by a dull clicking sound which is heard above the
plane of the connector housing with a sharp decrease in the engine speed
immediately after starting a cold engine.
At
main bearing, sound is accompanied by a strong, low tone sound is heard in the
parting plane of the crankcase with a sudden change of the engine speed. A
knock on the connecting rod bearing are sharper and sonorous, compared with
knock of main bearings.
It is
hearable at rotation area of the crank of corresponding cylinder. The
disappearance or significant decrease knock, when the ignition is off or the
nozzle in the cylinder, tells us about bearing malfunction.
Knock
of piston pin is sharp, clear, high-pitched. It is hearable in the area of
cylinder, in areas of upper and lower position of piston pin, changing the
speed of the crankshaft of the engine. A knock of piston pin must not be
confused with detonation knocking, which appear at a high angle of ignition
timing and disappear when it is decreasing. Symptoms of a crank mechanism in
cars "Opel" are also pressure reduction! at the end of the compression
stroke (compression) in the cylinders; the occurrence of noise and knocks
during engine operation; entering of gas into the crankcase, the increase of
oil consumption; oil dilution in crankcase due to the penetration of the vapor
mixture at the working cycles of compression oil flow into the combustion
chamber and getting it to the spark plugs, making the electrodes formed deposit
and deteriorating sparking. These faults lead to a reduction in engine power,
increase the content of CO in exhaust, increasing fuel consumption.
In
cars "Opel" diagnostics of crank mechanism condition, as well as the
timing is to determine the pressure at the end of the compression stroke
(compression), the definition of the vacuum in the intake pipe, the leakage of
compressed air from above piston space.
Compression
check must be carried out quickly, no more than 10 seconds. It is necessary
that there were at least seven cycles of compression. When checking compression
gasoline engines the air damper must always be open, and the throttle can be
closed or open. Due to the different amount of air entering to cylinders,
measuring compression by completely open throttle can detect the following
faults:
-
Deformation or valves burnout;
-
Failure and burnout of piston;
-
Coking of piston rings in the grooves;
- Cylinders surface malfunctions.
If
the compression is measured by closed valve, there can be determined defects of
cam profile of the camshaft in the construction of a hydropushers, hang the
valve if the valve mechanism with hydropushers, poor adhesion to the valve
seat.
Compression
measures tightness and characterizes the state of cylinders, pistons, rings and
valves and measured by using compression tester or kompressograf. These devices
are like manometer with a handle, tube, tip and slide device. The set of
compression tester or kompressograf for gasoline engines may include adapters
for connecting to the spark plug hole, and for diesel engines - the holes
nozzles or glow plug. Universal devices are equipped with multiple adapters in
different sizes for measurements in different types of engines.
These
faults are related with the wear parts of crank mechanism, and they are
eliminated when checking the technical condition and repair.
Before
checking of the technical condition of the crankshaft, crankshaft should be
wiped with gasoline, kerosene or solvent and carefully inspect it, to see if
there any traces at bearings, cracks, scratches, corrosion. For this, it is
repeatedly carried by coin or copper washer on the bearing. If on bearing
remains copper particles, so it is used, it must be reground. The presence of
traces on the crankshaft can determine if you hold them without pressing a
finger hands.
When
you have finished testing, you should clean the oil channels.
Next,
we should check radial beat of main bearing, and bias of bearing`s axis from
plane, which goes through connecting rod`s and main bearings. Also, we should
check non-perpendicularity of end`s
surface of the flange toward the axis of the crankshaft. By middle main
bearing, the beat is checked. It should be less than 0,025—0,030 mm, depends on
engine`s model.
After
fixing, the shaft is checked again for beat, and then shaft is installed in the
block of cylinders. After installing the crankshaft in the cylinder block, we
should check its axial backlash using the indicator. In the case of absence of
an indicator, the axial backlash is measured by less accuracy by using probe.
For that, a screwdriver is inserted between first crank shaft and front wall of
block`s cylinder, and push it to shaft of engine`s back. Then, using the probe,
define a gap between the end of rear washer of bearing and the plane of the
first radical neck collar. When backlash is more than needed, it is controlled
by a half-rings. By replacing old half-rings or by setting an increased
thickness of half-ring.
Literature:
1.
Shestopalov.S The device, service and repair of cars. - Moscow, 2009
2.
Repair of the car. National characteristics of garage repair: Trifonov. V - St.
Petersburg, Phoenix, 2008-416p.
3.
Repair of the car. Practical course: Vladimir Trifonov - St. Petersburg,
Phoenix, 2009, 576p.