Valve operation changing system of internal combustion engine

A valve operation changing system of an internal combustion engine, comprising:

• first and second cams formed on a camshaft and different in cam profile from each other;
• a rocker arm mounted on a rocker shaft and swingable around the rocker shaft to operate an engine valve upon engagement with said cams, said rocker arm being axially movable to engage with said first cam when said rocker arm is in a first position and to engage with said second cam when said rocker arm is in a second position;
• and
• means for selectively moving said rocker arm into one of said first and second positions in accordance with an engine operating condition, said moving means including:
• means defining first and second hydraulic pressure chambers which are fluidly connectable with an oil pressure source to be supplied with pressurized oil, said first hydraulic pressure chamber causing said rocker arm to move into the first position when fluidly connected with the oil pressure source, said second hydraulic pressure chamber causing said rocker arm to move into the second position when fluidly connected with the oil pressure source;
• a flow direction changing valve through which said first and second hydraulic pressure chambers are communicable with the oil pressure source, said flow direction changing valve selectively taking one of a first state to fluidly connect said first hydraulic pressure chamber with the oil pressure source and a second state to fluidly connect said second hydraulic pressure chamber with the oil pressure source;
• and
• valve means fluidly interposed between said flow direction changing valve and said second hydraulic pressure chamber, said valve means being openable to fluidly connect said flow direction changing valve with said second hydraulic pressure chamber in accordance with the rotational position of said cams.