Operation; Dohc (Swing Arm Type) + Vtec - Honda BF135A Manual

19. OPERATION

1. DOHC (SWING ARM TYPE) + VTEC

2. CHAIN DRIVE CAM DRIVE SYSTEM
3. INDEPENDENT CYLINDER HEAD/
CYLINDER BLOCK COOLING SYSTEM
1. DOHC (SWING ARM TYPE) + VTEC
STRUCTURE AND FEATURES
VTEC (BF150A only)
• The VTEC adapted on the BF150A outboard motors features the two cam profiles (for low and high engine speeds) and
the corresponding three rocker arms to drive the intake valve.
• Receiving the signal from the ECM, the VTEC solenoid valve turns the hydraulic pressure ON and OFF, moving the
rocker arm pistons built in the rocker arms and thereby combining and separating the three rocker arms to select either
of the two modes and two valve timings that are suitable for the running conditions (e.g. engine speed, load, etc.).
– When the engine speed is low [engine rpm is approx. 4,300 min
in the rocker arm. Each rocker arm is separate from the other making the independent movement. The center rocker
arm, designed for the high engine speed, turns idle and the right and left rocker arms trace to the low engine speed
cams. Therefore, the two intake side valves are driven in the low engine speed cam profile.
Thus, improvement of the torque in full throttle low speed range was realized compared to the conventional fixed
valve timing method.
– When the engine speed is high [engine rpm is higher than approx. 4,300 min
functions according to the signal from the ECM, extruding the rocker arm pistons from the rocker arm and combining
the three rocker arms. As the center rocker arm, which is designed for the high engine speed, traces to the high speed
cam, the two intake side valves are driven in the high engine speed cam profile.
Thus, the two valves function in the valve timing that is specially designed for the high speed range, which assures
improvement in engine horsepower.
DOHC
• The DOHC engine is adopted on these models, which realized center plug layout designed to contribute to improved
fuel consumption efficiency.
• Though the engine is the DOHC type, it also adopted the swing arm rocker arm, which allows valve clearance
adjustment with the adjusting screw and eliminated shim engagement that is poor in operationability.
EXHAUST CAMSHAFT
EXHAUST ROCKER ARM
VALVE ADJUSTING
SCREW
19-1
4. AIR/FUEL RATIO O
CONTROL BY A/F SENSOR
–1 (rpm) or below], the rocker arm piston is retracted
–1 (rpm)], the VTEC solenoid valve
INTAKE CAMSHAFT
INTAKE ROCKER ARM
(SWING ARM TYPE)
Built in VTEC system
VALVE ADJUSTING SCREW
CENTER PLUG ADOPTED
FEEDBACK
2