PATTAKON
Greece
VVA
on Side Cam Engines
(American
style V8, V6, V10, H-D V2 etc)
In
the first VVA side camshaft arrangement shown above, the cam lobe displaces the
bucket lifter and the pushrod. The pushrod, in turn, displaces a first rocker
arm. The first rocker arm displaces a free roller which in turn displaces a
second rocker arm which finally displaces the valve. Depending on the rotation
angle of a control shaft, the stroke of the valve varies continuously, while
the valve clearance remains constant.
Compared
to the second VVA side camshaft arrangement shown below, the first arrangement
is preferable.
In
the first arrangement the full cam lobe action is initially conveyed to the
cylinder head, i.e. close to the valve, and only then the mechanism with the
free roller modifies the cam lobe action into a long or shorter stroke of the
valve, depending on the angular position of the control shaft.
The
second arrangement, with the free roller directly activated by the cam lobe,
cannot be so precise at short lifts, exactly where the precision is required,
because the in-between joints and the elasticity of the members involved to
convey the cam lobe action to the cylinder head, cannot transfer accurately
short lifts to the valve, for instance lifts of 0.2 to 0.3 mm.
It
is also a matter of accessibility, of space and of cost.
Upgrading
a side cam engine, for instance a Vee eight, according the first arrangement,
all modifications concern exclusively the cylinder head, where there is easy
access, plenty of space to install the new components and some ready supporting
means, like pivot shaft, for the rocker arms and the control shaft.
On
the contrary the upgrade of a side cam engine according the second arrangement
needs serious modification of the block, while the space and the accessibility
in the camshaft area are not the desirable.
Click
SideCam to download the relevant
animation (0.6 MB) and then open it.