As the rockers "tilt" and push down on the valves there is a horizontal
component due to the fact that the rockers are pivoting on an axis. When you
put in a cam with higher lift, the horizontal component of force applied to
the valve increases. This can cause increased wear in the valve guides and
on the lobe of the rocker. In addition, the friction associated with rubbing
the rocker lobe back and forth accross the valve stem robs power and causes
wear on the rest of the valve train. To overcome this the roller rocker has
a roller on the end of the rocker where it contacts the valve stem
eliminating the effects of the horizontal component and reducing the
friction in the valve train.You can change the valve lift by changing the
cam or by changing the ratio of the rocker assembly. Really an unnecessary
cost unless your doing some serious mods to your engine IMHO.
Chris Reichle
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The main advantage of roller rockers is to lessen the parasitic losses
from the valve train. Our LBCs valve lift is pretty modest, not much
more than a third of an inch, but that still requires our little rockers
to tilt something like 30+ degrees. That is a lot of rotation and force.
The cups at the end of the pushrods keep everything in contact but there
is some stress there and the rocker shafts can wear. I don't know how
you would replace the bushings in those rockers. I guess it only takes
money.
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