head cover 3 a chain case 4 and an oil pan 5 the engine block 2 includes a cylinder block 21 and a cylinder head 22 the cylinder block 21 has a crankshaft 23 the cylinder head 22 is mounted on the cylinder block 21 the cylinder head 22 has a pair of camshafts 24 the camshafts 24 are located parallel to the crankshaft 23 on the intake and exhaust sides individually as shown in fig2 and 4 a cooling water inlet 22 b through which cooling water flows into the cylinder head 22 opens at a front wall 22 a of the head in the present embodiment the rotation axis of the crankshaft 23 extends along a longitudinal front back direction of the engine the side on which the chain case 4 is attached to the engine block 2 is the front side which defines the transverse left right direction the vertical direction is the direction in which the cylinder block 21 and the cylinder head 22 are put on each other the upper side is the side on which the cylinder head 22 is situated with respect to the cylinder block 21 on the other hand the engine 1 is provided with a power transmission system 25 the power transmission system 25 links.