Whenever
a rocker arm is ROTATED on the stud of a head that has IN-LINE valves
(as viewed from the end of the head), this is the effect that is
created. There's no other way around it. Yet, to this day, countless
heads are sold with offset pushrods, and WORSE, offset studs that FORCE
the engine builder to "presume" this is for a proper design reason, when
in fact it is GROSSLY bad engineering, or bad judgment. Any heads that
have studs with a compromised offset from what the pushrod is, induces
false trust to the engine builder that a stud mounted rocker will
operate properly as long as the three points are connected: PUSHROD,
STUD and VALVE. Not so! You will need STUD rockers that have a designed
offset in the roller and pushrod cup, to use with such heads. OR... you
will need STAND mounted rockers (also known as "shaft" rockers).
If you don't, then just
like the illustration above, the roller will be tilting to one side and
only applying pressure by its side edge to the valve in a
side-loading arc, regardless of what you do to the rocker height.
Adjustments to the rocker height will only change the point of valve
lift where maximum MISALIGNMENT occurs, but it will occur! Do yourself a
favor, buy stand mounted rockers, or buy stud mounted rockers with the
offsets on both the roller and pushrod, or better yet: if you are
determined to use stud mounted rockers and can have the option from the
head manufacturer, BUY the HEADS
with the rocker studs drilled and tapped on the SAME Center-line as the
valve spacing. Leave the pushrod offset entirely in the rocker. MEI's PVS
Product Group just
happens to offer such an animal. :-)
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The above
budget brand rockers even have an offset
pushrod which should have minimized the above "twist" to aid a very bad head design, but to no avail. In spite of this, these aftermarket heads have
such misaligning STUD placement for the pushrod offset, that this TWIST is the BEST
result that could be obtained. This is a great
example of what NOT to do!
^
