Engine decompression device and engine

An engine comprising:

• a valve mechanism configured to operate an intake valve and an exhaust valve in accordance with rotation of a crankshaft, the valve mechanism including:
• a timing gear fixed to the crankshaft;
• a camshaft that rotates in conjunction with rotation of the timing gear;
• a first lifter abutting an intake valve cam of the camshaft;
• second lifter abutting an exhaust valve cam of the camshaft;
• a first rocker arm including a first end portion abutting the intake valve, and a second end portion connected to the first lifter via a first push rod;
• a second rocker arm including a first end portion abutting the exhaust valve, and a second end portion connected to the second lifter via a second push rod;
• and
• a pair of valve springs each configured to respectively bias the intake valve and the exhaust valve in a closing direction;
• and
• a decompression device including:
• a decompression weight rotatably provided on the camshaft via a pivot;
• a decompression spring configured to bias the decompression weight;
• and
• a decompression shaft including an engagement pin that is guided by a guide groove formed in the decompression weight, a decompression cam provided on a cam surface of the intake valve cam or the exhaust valve cam so as to alternately advance and retract, and a connection portion that connects the engagement pin to the decompression cam,
• wherein, when the decompression weight rotates against a biasing force of the decompression spring due to a centrifugal force, the decompression shaft rotates such that the decompression cam moves from an advanced position where the decompression cam protrudes from the cam surface to a retracted position where the decompression cam is retracted from the cam surface,
• wherein the decompression weight is further formed with a rotation restricting groove continuous with the guide groove, the rotation restricting groove configured to restrict a reverse rotation of the decompression shaft so as to prevent the decompression cam from moving to the retracted position due to a force acting on the decompression cam when the engine is stopped, and
• wherein the rotation restricting groove is provided at a connecting portion between the guide groove and an inner peripheral portion of the decompression weight.