Variable Valve Timing
The variable valve timing system improves low
and high speed engine performance, engine idle
quality and exhaust emission. It is a two position
system that operates on the intake camshafts
only. There are 30° of crankshaft movement
between the retarded and advanced positions.
Engine oil pressure operates the system under
the control of the ECM.
For each intake camshaft there is a valve timing
unit, a bush carrier assembly and a valve timing
Valve Timing Unit
The valve timing unit turns the intake camshaft in
relation to the primary chain to advance and
retard the timing.
The unit consists of a body and sprocket
assembly separated from an inner sleeve by a
ring piston and two ring gears. A bolt secures the
inner sleeve to the camshaft. The ring gears
engage in opposing helical splines on the body
and sprocket assembly and on the inner sleeve.
The ring gears transmit the drive from the body
and sprocket assembly to the inner sleeve and,
when moved axially, turn the inner sleeve in
relation to the body and sprocket assembly.
Engine oil pressure (controlled by the valve timing
solenoid) moves the ring gears and piston to turn
the inner sleeve in the advanced timing direction.
A return spring moves the ring gears and piston
to turn the inner sleeve in the retarded timing
Additional springs absorb backlash to reduce
noise and wear. The springs between the ring
gears absorb rotational backlash. The spring
between the inner sleeve and the end of the
body and sprocket assembly absorbs axial
VALVE TIMING DIAGRAMS
65° 50° 35° 50°