Abstract: A decompression device is attached to an exhaust camshaft, and the exhaust camshaft is supported by a cylinder head. The decompression device includes a decompression camshaft formed with a decompression cam that can protrude and be immersed with respect to a base circle of an exhaust cam of the exhaust camshaft, a decompression arm that moves in an opening direction due to centrifugal force accompanying rotation of the exhaust camshaft to protrude the decompression cam, and a spring that moves the decompression arm in a closing direction by spring force resisting the centrifugal force to immerse the decompression cam. In the decompression device, the opening direction of the decompression arm can be changed in a same direction or in an opposite direction to a rotation direction of the exhaust camshaft for each cylinder.

Abstract: A motorcycle has a crankcase containing a crank shaft and a balancer shaft, and a cylinder and a cylinder head positioned above the crankcase, and an exhaust pipe extends from the cylinder head. The balancer shaft is positioned in front of the crank shaft, and the crankcase has a balancer shaft housing supporting the balancer shaft thereinside, and has a recessed part depressed rearward in a front end center part of the balancer shaft housing. The balancer shaft has balancer shaft weights apart from each other in one side and in the other side in an axis direction.

Abstract: A motorcycle has a crankcase containing a crank shaft and a balancer shaft, and a cylinder and a cylinder head positioned above the crankcase, and an exhaust pipe extends from the cylinder head. The balancer shaft is positioned in front of the crank shaft, and the crankcase has a balancer shaft housing supporting the balancer shaft thereinside, and has a recessed part depressed rearward in a front end center part of the balancer shaft housing. The balancer shaft has balancer shaft weights apart from each other in one side and in the other side in an axis direction.

Abstract: An oil passage structure for an engine of a vehicle is provided with a connecting rod swingably coupled to a crankshaft rod by a plurality of crankpins, the plurality of crankpins being disposed between a plurality of crank journals, and a plurality of support portions for rotatably supporting the crankshaft by the plurality of crank journals in a cylinder block. The crankshaft has a first oil passage formed therein, the first oil passage supplying oil from an opening formed in one end face thereof to sliding surfaces of the plurality of crankpins, the plurality of support portions have a second oil passage formed therein, the second oil passage supplying the oil to a sliding surface of each of the plurality of crank journals, and the first oil passage and the second oil passage communicate with each other in some of the support portions and in some of the crank journals.