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Unformatted text preview: arm is generally of
I-section but for low speed engines, it can be of rectangular section. Due to the load on the valve, the
rocker arm is subjected to bending moment.
l = Effective length of each rocker arm, and
σb = Permissible bending stress.
We know that bending moment on the rocker arm,
M = Fe × l
We also know that bending moment,
M = σb × Z
Z = Section modulus.
From equations (i) and (ii), the value of Z is obtained and thus the dimensions of the section are
4. Design for tappet. The tappet end of the rocker arm is made circular to receive the tappet
which is a stud with a lock nut. The compressive load acting on the tappet is the maximum load on the
rocker arm for the exhaust valve (Fe).
dc = Core diameter of the tappet, and
σc = Permissible compressive stress for the material of the tappet which
is made of mild steel. It may be taken as 50 MPa.
We know that load on the tappet,
Fe = (dc ) σc
From this expression, the core diameter of the tappet is determined. The outer or n...
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- Spring '11