Engine abnormal sound

1. Timing gear chamber makes abnormal sound

There’re many factors that may cause abnormal sound of engine. If there’s obvious
mechanical noise on the front of engine during running and this sound becomes
obviously loud especially when compressor is filled with air normally, but obviously
low when the pressure regulating valve is releasing air(compressor running without
load), usually the drive mechanism of timing gear chamber malfunctions. At this
moment, it is noted that vehicle cannot run by force, and should be driven to a repair
trench and dismantle oil pan and check if there’s foreign mechanical matters in the
engine oil of the oil pan. If broken gear is found, it means gear of timing gear system
is broken. Aim at timing gear chamber by illumination (flash light), and rotate
flywheel of engine and observe gear breaking position. If other mechanical stuff is
found, it is required to analyze position of stuff. At this moment, check on timing
intermediate gear bearing and compressor bearing and injector pump driving bearing
is specially needed, and in fact, timing intermediate gear and injector pump driving
shaft support bearing easily encounters a fault “falling apart”. When finding failure
position, dismantle and repair on failure position (see section “Engine Installation” for
details) For old structure, use two 3 high speed bearings on timing intermediate gear,
and the bearing cannot be replaced by common Chinese-made 206 bearing, otherwise,
it will make frequently falling apart on bearing.
If continue driving the vehicle, damage will be worsened; and once crankshaft is
damaged, replacement of crankshaft gear will become very difficult.
2. Air valve is making noise
It is easy to judge air valve noise because noise position is relatively obvious;
especially when engine is running in low speed, noise is more obvious. The main
reason of valve noise is valve gap. If a certain valve gap in cylinder has much
difference from other valves obviously, it is required to check carefully if adjusting
bolt is loose, valve spring is broken, or the valve lever is bent or broken.
3. Cylinder noise
There are many causes on abnormal noise of engine cylinder. First, injector spray is
not good and it will make noise on cylinder, followed with smoke emission. Check
the noise by fuel cut-off. Injector poor atomization will cause unstable engine
running; long term poor atomization will also result in cylinder knocking incident
because unburned diesel has flush function on lubrication of cylinder. In more serious
case, oil amount in oil pan will increase gradually.
Inconsistent injection amount in injector pump will also cause cylinder knocking.
Cylinder with obvious more injection amount will have cylinder knocking
phenomenon. Fuel cut-off method can be used to judge which cylinder has too much
fuel injection obviously. After reducing the cylinder fuel injection amount, (loosen
cylinder injector joint by a spanner), cylinder knocking can disappear obviously.
Serious cylinder scuffing, cylinder sticking and piston ring seizure, etc can make
cylinder knocking noise. Meanwhile, the fault is accompanied with crankshaft case
gas carry-over; if single cylinder sound is obvious and gas carry-over occurred one by
one string, which indicates that a certain cylinder is scuffing seriously. Sound noise
caused by cylinder scuffing cannot be eliminated by fuel cut-off, but can be
weakened. In case of slight cylinder scuffing (cylinder piston is not damaged
seriously, but just has a slight grinding and matching is not over usage limit), there is
no need to change cylinder sleeve piston, and it is ok to repair it through replacement
of piston ring. The engine repaired in this manner shall run under proper temperature
and loading during run-in period, and then bear safe load after run-in period. In case
of serious cylinder scuffing, cylinder sleeve, piston and piston ring subassembly must
be changed.

Fig.1-2 Method of pulling cylinder sleeve

Replacement method is to dismantle cylinder cover with scuffing fault, remove the
engine oil pan, dismantle linkage lever and pull out piston linkage subassembly. Pull
out cylinder sleeve with special tools as shown in fig. 1-2, and dismantle piston
subassembly from linkage. Choose piston and cylinder according to requirement of
matching gap, clean cylinder hole and hole concave, then wipe hole and outer
diameter grease by trichloroethylene, and smear Mos2 powder on the surface of
cylinder, and try to choose the cylinder sleeve suitable for the gap of cylinder hole. In
this way, it will be easy to press bush into hole by hand or simple tools(see section
“Engine Installation for details). Check if the cylinder sleeve is higher than top
surface of the cylinder block within range of 0.05 ～ 0.10. Heat the new piston
subassembly (note that piston is matched with the engine model) to 80℃ for 10
minutes and then fit it with the linkage. Please note the installation location of the first
and second air ring; surface of the ring marked with “TOP” or other letter mark must
be upward. The 3rd ring’s opening shall be staggered with 120° before installation
into cylinder sleeve and the ring opening shall be 30° out of piston pin axis. Remove
the piston and the linkage subassembly from bush by special tools. Note the
installation location of piston and linkage, location of linkage subassembly and
cylinder sleeve. Tighten linkage bolts with specific torque Note that linkage bolt can
be only used for one time, which means that linkage bolt must be changed each time
when dismantling linkage. When cylinder cover, valve tappet and valve chamber
cover are mounted, repair is finished. Specific consequence (see section “Engine
Installation for details) and torque should be followed when mounting cylinder cover,
and main and vise bolt of cylinder cover should be tightened.
When cylinder sleeve or piston is seriously worn out, and bush piston gap have
exceeded limit will also make noise, and the sound cannot be eliminated by fuel cut-
off. After decomposition, it is found that steps appear on cylinder mouth. At this
moment, sleeve and piston subassembly should also be replaced.
If cylinder knocking happens after replacement of timing belt, the sound position is
obvious and becomes loud with acceleration of engine, and note not to drive it any
more. First, it is required to check mark of timing gear and timing mark, that is 1st
cylinder TDC(1st cylinder TDC flywheel “TO” scale line should be aligned with the
flywheel shell scale line, the 1st cylinder intake and exhaust valves should be closed).
Check if the timing mark on camshaft gear is aligned with the scale line in the timing
shell. Even if the scale line misplaced for one gear, it will cause the sound of cylinder
knocking, and will damage piston and valve in more serious case, and even serious
incident of damage cylinder, etc.
If loud abnormal sound is made suddenly during running, it is required to stop
running immediately, and conduct inspection carefully. Because obvious abnormal
sound suddenly always results from damage of mechanical parts such as valve spring
is bent, and valve drop into cylinder, valve bent or valve seat drop into cylinder,
sleeve broken and even damage, linkage bolt broken causing drop of linkage cover,
serious damage due to timing intermediate gear support fall apart. This kind of fault
will lead to serious consequence, and should pay extra attention to it.
4. Bearing bushing sound
If main bearing bushing or linkage bearing bushing is worn out seriously or burnt out,
it will make bearing bushing noise. Cause to common noise of bearing bushing is
difficult to judge. The characteristic of linkage bearing noise is clear, and when engine
is accelerating suddenly, the sound is obvious, and the sound is increased as rising of
rotation speed and load. Fuel adding can be continued when checking, and there will
be “dada” sound obviously, and it will be weakened with fuel cut-off method. The
characteristic of main bearing bushing noise is that the noise is tediously, and
becoming loud with acceleration of engine, and it is obvious when accelerate
suddenly. Check it with fuel cut-off test, single cylinder fuel cut-off without obvious
change, and two neighboring cylinder beside failure cylinder fuel cut-off sound is
decreasing obviously. The main reason of bearing bushing noise (or worn out or
burning) is that oil is too dirty, and impurities enter into shaft journal and bearing oil
slick, thus bearing is worn out, and lack of oil, and fuel feed is not enough, and it is
difficult to form enough oil membrane between axle hole and journal. In lubrication
system, the gap of certain part is too much and lead to leakage of oil, lubrication is not
good, the gap between the journal and the bearing bushing is too much, and engine
overheat, etc. It is noted that WD615 series diesel engine is high intensified diesel
engine, and it is required to use AP1CD grade and AP1CF grade(Euro II engine with
300 hp and Euro III engine) supercharge diesel engine (see section “Oil, Water and
Power” ).This requirement should be followed without any compromise. If other low
grade oil is used, bearing bushing burning failure will occur in short time. Intensify
diesel engine high grade oil, and its physical and chemical performance index can be
identified by test, but relevant characteristics such as clean disparity, anticorrosion,
anti-foam, oil membrane intensity cannot be checked by simple physical and chemical
test. Moreover, it is required to judge if intensify characteristic loses, and this point is
difficult to reach in some companies. So it cannot judge oil is in failure only by
simple physical and chemical experiment, thus wrongly extend oil change period. It is
better to change oil strictly according to oil change interval under different working
conditions specified in user manual.
There’s another obvious sound, especially at idle, engine has “dang, dang” rhythmic
sound, and when depressing clutch pedal, noise disappears. Generally speaking, it
results from big axial gap of crankshaft when the crankshaft is making axial sudden
movement. At this moment, it is required to change crankshaft spacers.