Service / Technical
Stroke : Single direction movement of the piston, When the piston moves up from BDC to TDC or TDC to BDC, the single direction movement of the Piston in one direction is called ‘Stroke’.
Bore : The bore is inside Diameter of Cylinder
RPM : Revolution per minutes
Effect of bore and stroke on engine performance : Engines of the same displacement vary in character depending on “bore and stroke”. Short stroke engines : Stroke is smaller than bore diameter. Square engines : Stroke and bore diameter are even. Long stroke engines : Str oke is larger than bore diameter.
Compared with a long stroke engine, the square or short stroke type is easy to raise the engine speed and develop high power. If the engine speeds are the same, the piston speed is slower and friction resistance can also be reduced. Among other merits are the lower overall height and compact design. Therefore, the square type and short stroke engines are dominant.
Displaced Volume: The compression ratio indicates to what extent the air – fuel mixture is compressed when piston is at TDC.
Combustion Chamber volume: The volume of space between the cylinder head and the piston at TDC is called “combustion chamber volume”.
Compression ratio: The compression ratio indicates to what extent the air – fuel mixture is compressed when piston is at TDC in compression stroke.
The higher Compression ratio is used for High speed Vehicles.
Compression Ratio :
Volume of Combustion chamber (v) + Displacement (v) divided by Volume of Combustion chamber (v)
Torque : The turning force exerted on rotating parts is called “torque”. Motorcycles are driven by the torque of the crankshaft.
Torque = Force × distance (kg•m N•m = kgN × m)
Change in torque (Primary and secondary reductions ,and speed reduction from the gear box).
The greater the number of gear teeth, the greater the torque. However, the rotational speed is reduced.
The “maximum torque” is indicated along with the engine speed at which maximum torque is delivered.
When a motorcycle is run at maximum torque, the rear wheel driving force is at the maximum.
Difference between BHP (Brake Horse power) & PS (Pfred Scale ) : Both are the unit of Power
1 Bhp = 1.0143 Ps
Single Over Head Cam Shaft (SOHC) : In this type of Cam Mechanism, Cam shaft is positioned in the cylinder head & driven by Cam Chain to operate Inlet & exhaust valve thru Rocker arms.
In this type mechanism Lesser parts are used to operate valves hence operation is stable even at high speed.
Trochoid Type Oil Pump : Two rotors rotating at different Speeds causing variations in the volume between them. This Variation in volume causes oil flow in and out of the Pump. The Trochoid Pump is more commonly used due to its advantages and compact design.
Four Stroke Engine
Basic construction: A 4-stroke engine requires two complete revolution of the crankshaft (4 strokes of the piston) to complete a full cycle (Intake, Compression, Combustion and Exhaust).
Power stoke: A power stroke takes place on every other full rotation of the crankshaft. The cylinder head has two ports. An intake and an exhaust. Valves control the opening and closing of these ports. The opening and closing of the valves is timed to piston movement and location in its travel.
All air/fuel mixture compression takes place above the piston.
Advantages: Intake, compression, combustion and exhaust occur independently, so operation is more precise, efficient and very stable.Fuel loss caused by “stroke” over lap is less than 2-stroke. Fuel consumption is lower.
Single Axis Balancer
As engine runs, vibrations are caused from inertia force created by motion of engine Components (Piston & Connecting rod).
In order to lessen the vibration a balancer weight is added on a axis positioned at an angle above Crank Shaft and made to rotate in the opposite direction of Crank Shaft to reduce engine vibrations.
Wet Sump system : Oil is stored in the oil sump in bottom of crank case, from here oil is pumped under pressure to various parts of the Engine. Oil is fed to both the Crank Shaft & Valve Train.
The Crank Shaft assembly is lubricated with the same oil used to lubricate the Transmission & Clutch .The oil is fed directly from the Oil Pump. The Cylinder & Piston are lubricated by splash oil that previously lubricated the Crank pin & connecting rods. The Valve Train is also lubricated by Pressure fed oil. After lubrication , the oil returns to the sump (Oil Chamber).
Diamond Frame: In this type of Frame the Engine is mounted at five locations (One at the top & two each at the front & rear of the Crank cases) and used as a stressed member of the frame for better stability, less vibrations & light weight The large size & thickness of the main pipe provide extra rigidity.
What is BS type Carburetor and what is the benefit of that for the user?
The BS carburetor ( ‘B’ stands for butterfly valve and ‘S’ for SU, designating the maker Skinner Union.)
In this type of the Carburetor, the air-fuel mixture is controlled by the regulation of the Engine Intake vacuum (negative pressure) which results in smooth operation of the vehicle, stable idling & good fuel economy.
Also due to this carburetor, the user gets smooth acceleration, even if the rider opens or closes the throttle sharply.
YTPS technology and its benefit: Yamaha Throttle position sensor (YTPS) is a unit fitted on the carburettor on same axis of Butterfly valve.
It is adopted in order to control the ignition timing for each engine RPM. This helps to ensure excellent combustion efficiency and hence smooth throttle response, superior fuel economy and less emissions.
With the use of YTPS technology, 3- dimensional digital mapping has been done among, engine revolution, ignition timing and throttle opening for optimum combustion their by ensuring maximum mileage.