2.13.1.5 Selection Table for Tappet Rod of Exhaust Valve 

 

 

Installed tappet rod 

thickness (mm/in)  Clearance 

measureme

n mm(in.) 

935

2.13.2 Description and Operation 

2.13.2.1 Description and operation 

1. Cylinder 

Hood 

Cylinder hood is made from aluminum alloy casting process. Cylinder valve stem is a mechanical 
system. Valve clearance can not be automatically adjusted, which is very important. The cylinder 
valve is an integrated part. OEMs can offer 38 different sizes for  choosing. During the 
maintenance, required quite tube thickness can be calculated according to the formula. For details, 
refer to 2.13.8.20 Valve Clearance Adjustments. The camshaft is arranged in a double-top mode; a 
VVT actuator is further arranged on the inlet camshaft driving chain for regulating the air inlet 
timing. The specific operation principles refer to 2.13.3.1 Operation Principle of System. 

2. Timing 

chain 

Double overhead camshaft is driven through a timing chain. The timing chain must be replaced 
every one hundred and twenty thousand kilometers. The timing chain system consists of a timing 
chain, a timing chain guide rail, a timing chain tensioning rail and a timing chain tensioner acted 
on the timing chain tensioning rail. Where, the tension pressure of the timing chain tensioner is 
provided by the oil pump to ensure that the tension of the timing chain keeps balanced. The timing 
chain is lubricated by an engine oil nozzle installed on the engine oil pump. The specific 
information refers to 2.13.8.11 Check Timing Chain. 

3. Intake 

Manifold 

Intake manifold has four independent long ports, using inertia to improve the engine torque at low 
speed. 

4. Camshaft 

Dual overhead camshaft (DOHC) has two camshafts. A camshaft controls the intake valves, the 
other camshaft controls the exhaust valves. The camshaft is located in the journal in the cylinder 
hood on the top of the engine and fixed with camshaft cover. The cylinder hood camshaft journal 
drilling is used for engine oil channel. Engine oil flows to the camshaft under pressure, lubricating 
each camshaft journal. Engine oil flows through the cylinder hood to return to oil pan. Cam 
convex corner is formed by machining, at the right time, according to the appropriate amount, 
accurately open and close intake and exhaust valves. Cam convex is lubricated by high-pressure 
oil escaped from the engine camshaft. 

936

2.13.3 System Operating Principle 

2.13.3.1 System operating Principle 

1. Reciprocating Piston Engine Operating Principle:

 

z  Intake Stroke: the crankshaft driven piston moves from TDC to BDC. At this point exhaust 

valve closes, intake valve opens. In the piston moving process, the cylinder volume gradually 
increased and the vacuum is formed within the cylinder. ECM controlled fuel injectors spray 
fuel into the intake pipe. At this time the intake valves open, air and fuel mixture sucked 
through the intake valve into cylinder and forms a combustible mixture. 

z  Compression Stroke: At the end of the intake stroke, crankshaft continues to drive the piston 

from the BDC to the TDC. Intake and exhaust valves are closed. With the piston moving up, 
the cylinder volume became smaller and smaller. Because gas is compressed, the temperature 
of the compressed gas rose rapidly. 

z  Power Stroke: At the end of compression stroke, the primary coil circuit of ignition coil 

controlled by ECM is disconnected and the secondary sensor produces a high voltage, which 
passes rapidly through the cylinder hood to the top of the spark plug, and finally the 
high-voltage breaks through the spark plug gap to generate electric spark, igniting the 
combustible mixture within the cylinder. Fire spreads rapidly inside the combustion chamber, 
while releasing a large amount of heat. Combustion gas expands rapidly .The pressure and 
temperature    also increases. Swelling force acts on the piston top, prompting the piston to 
move from the TDC  to the BDC and changing piston reciprocating motion into rotary 
movement through the connecting rod. At this point, intake and exhaust valves are still 
closed. 

z  Exhaust Stroke: At the beginning of the exhaust stroke, exhaust valve opens, intake valve is 

still closed. the crankshaft connecting rod drives the piston from the BDC to the TDC. After 
burning, the expanded gas residue will be discharged through the exhaust valve to outside the 
cylinder by its own pressure and the piston movement. When the piston reaches the TDC, the 
exhaust stroke ends and exhaust valve closes. 

But in the actual process, the intake valve opens before the TDC and closes after BDC. This 
design is intended to draw more air into cylinder and reduce the power consumed in the intake 
process. In the exhaust process, the exhaust valve opens before BDC and closes after TDC. The 
aim is to reduce the mixture within the cylinder and reduce the power consumed in the intake 
process. Because intake and exhaust valves have a certain overlap angles, namely, at a certain 
crank angle intake and exhaust valves open at the same time. At this time the gas discharged 
through the exhaust valve forms a certain amount of inertia and draws the mixture into the 
cylinder. This will draw more air into the cylinder. But the valve overlap angle is not the bigger 
the better. In different operating conditions, the valve overlap angle requirements vary, therefore, 
in this engine there is intake valve variable valve timing, which aims to meet the engine intake 
valve opening angle requirements at different operating conditions. This function is achieved But 
the valve overlap angle is not the bigger the better. In different operating conditions, the valve 
overlap angle requirements vary, therefore, in this engine there is intake valve variable valve 
timing, which aims to meet the engine intake valve opening angle requirements at different 
operating conditions. this function is achieved through the VVT system. 

2.  VVT system working principle 

VVT full write    is Variable Valve Timing. Where there is mass, there is inertia. The air drawn 
into the engine cylinders also has inertia, after the intake process the air tends to help enter into the 
cylinder. At this time if the valve closing time is delayed, more air will be drawn into the cylinder, 
so that volumetric efficiency will be improved. As a result, the longer the delay in valve closing 
time, the better the High-Speed performance; On the contrary the more advanced valve closing, 
the better performance and the more torque at the Low-Speed. 

937

(1)  With VVT Valve Timing Diagram

 

排气门

进气门

持续开启角度：232度

持续开启角度：240度

调整最大提前角

调整最大滞后角

TDC

ATDC 4

度

ATDC20度

ABDC80

BBDC48度

ABDC30度

BTDC30度

BDC

TDC

BDC

TDC

BDC

FE02-2065b

   

TDC: Top dead center 

BDC: Below dead center 

ATDC: After Top dead center 

BTDC: Before Top dead center 

ABDC: After Below dead center 

BBDC: Before Below dead center

 

(2) VVT 

Control Strategy 

Driving Conditions 

Intake Valve Timing 

Cause 

Low-Load Lag 

Steady 

Combustion 

High Load, High Speed 

Lag 

Increased Output Characteristics 

High Load, Low Speed 

Advance 

Increased Torque 

Medium-Speed Condition 

Advance 

Improved Fuel Consumption 
Performance 

(3) Advance Process 

When the engine is in normal operation, the oil pressure generated by an oil pump plays the role 
on the VVT electromagnetic valve. ECM controls the VVT solenoid valve by means of pulse 
width modulation signals. When needing VVT to regulate the intake valve in the maximum 
position in advance, the ECM controls the VVT electromagnetic valve opening as 100%. At this 
time, the engine oil pressure is applied to the advancement cavity and the VVT rotor blades 
displace in the opposite direction to the crankshaft rotation angle to stop in the maximum position 
finally. 

A VVT actuator commonly stays at about 8? when idling without load. Because the 
mechanical value of the opening angle of an intake valve is 5?, the actual opening 

 

Air intakevalve 

Air exhaust door

Continuous open 

angle:232degree 

ATDC4degree 

BBDC48 

degree 

Continuous open angle:240 degree 

Adjusting max.advance angle

Adjusting max.retard angle 

BTDC30 

degree

ABDC30 

degree 

ATDC20 

degree 

938