Switchable rocker arm

A rocker arm for transmitting rotational motion from a camshaft to opening and closing motion of a combustion valve in an internal combustion engine, said rocker arm comprising:

• an outer arm defining a lock pin bore which is centered about, and extends along, a lock pin bore axis;
• an inner arm which selectively pivots relative to said outer arm about a pivot axis which is parallel to said lock pin bore axis, said inner arm including a protrusion which defines an inner arm stop surface which is planar;
• a lost motion spring which biases said inner arm to pivot relative to said outer arm in a first rotational direction;
• and
• a lock pin disposed within said lock pin bore, said lock pin having a lock pin slot extending thereinto and also having a lock pin stop surface which is planar, wherein said lock pin is displaced within said lock pin bore between 1) a coupled position in which said lock pin stop surface is aligned with said inner arm stop surface, thereby preventing said inner arm from pivoting relative to said outer arm past a predetermined position of said inner arm relative to said outer arm in a second rotational direction in which said inner arm stop surface contacts said lock pin stop surface, said second rotational direction being opposite of said first rotational direction and 2) a decoupled position in which said lock pin slot is aligned with said protrusion such that said inner arm is allowed to pivot relative to said outer arm past said predetermined position in said second rotational direction such that said protrusion extends into said lock pin slot when said inner arm is pivoted past said predetermined position.