An internal combustion includes: a camshaft having a metal core rod insert formed centrally in the camshaft and a driven gear, an exhaust cam, etc. formed of resin integrally with the camshaft; and a decompression mechanism. The decompression mechanism includes: a pair of supporting protrusions provided on the driven gear and each having an insertion hole; a decompression member having a pair of projections disposed between the supporting protrusions; and a biasing spring disposed between the projections for normally biasing the decompression member toward the exhaust cam. The camshaft also has a guide recess and a balancing recess formed in opposite sides of the camshaft, and the metal core rod is exposed through the guide recess and the balancing recess.

A synchronous drive is provided in which a non-circular rotor generates a fluctuating corrective torque to counteract a fluctuating load torque on a driven rotor. The angular orientation of the non-circular rotor can vary relative to the driven rotor so as to change the phase angle of the fluctuating corrective torque relative to the driving rotor. The arrangement may be applied in internal combustion engines with variable valve timing (VVT) systems, wherein the phase angle of a fluctuating load torque presented on a cam rotor, due to forces arising from actuation of intake and/or exhaust valves by the camshaft, varies relative to the crankshaft. The phase angle of the fluctuating corrective torque is also varied relative to the crankshaft to maintain phase relationship with the fluctuating load torque and thereby maintain reduced cam torsional vibrations and span tensions provided by the non-circular rotor during operation.

A synchronous drive is provided in which a non-circular rotor generates a fluctuating corrective torque to counteract a fluctuating load torque on a driven rotor. The angular orientation of the non-circular rotor can vary relative to the driven rotor so as to change the phase angle of the fluctuating corrective torque relative to the driving rotor. The arrangement may be applied in internal combustion engines with variable valve timing (VVT) systems, wherein the phase angle of a fluctuating load torque presented on a cam rotor, due to forces arising from actuation of intake and/or exhaust valves by the camshaft, varies relative to the crankshaft. The phase angle of the fluctuating corrective torque is also varied relative to the crankshaft to maintain phase relationship with the fluctuating load torque and thereby maintain reduced cam torsional vibrations and span tensions provided by the non-circular rotor during operation

The valve timing changing device includes a vane rotor 10 that rotates integrally with a camshaft around an axis S of the camshaft and includes a lock pin 42; and a housing rotor Hr that is rotatable relative to the vane rotor around the axis within the range of a predetermined movable angle and whose relative rotation is locked by the lock pin. The housing rotor Hr includes a toothed member 30 having a tooth row 31 to which a driving force is applied, and a bottomed cylindrical housing member 20 fixed to the toothed member and accommodating the vane rotor. The housing member 20 is formed with a center of gravity eccentric from the axis S on a side that relatively reduces an imbalance amount m1 of the vane rotor.

The valve timing changing device includes a vane rotor 10 that rotates integrally with a camshaft around an axis S of the camshaft and includes a lock pin 42; and a housing rotor Hr that is rotatable relative to the vane rotor around the axis within the range of a predetermined movable angle and whose relative rotation is locked by the lock pin. The housing rotor Hr includes a toothed member 30 having a tooth row 31 to which a driving force is applied, and a bottomed cylindrical housing member 20 fixed to the toothed member and accommodating the vane rotor. The housing member 20 is formed with a center of gravity eccentric from the axis S on a side that relatively reduces an imbalance amount m1 of the vane rotor.