Internal combustion engine

An internal combustion engine comprising:

• a crankcase;
• a cylinder provided on the crankcase and equipped with a cylinder bore;
• a crankshaft provided in the crankcase and rotatably supported;
• a balancer mechanism provided in the crankcase and configured to reduce vibration of the internal combustion engine by power transmitted from the crankshaft;
• a breather chamber provided on a top surface of the crankcase and disposed behind the cylinder;
• and
• a lubrication system provided in the crankcase and configured to supply lubricating oil to the crankshaft and the balancer mechanism,
• wherein the balancer mechanism includes:
• an idler gear rotated by power transmitted from the crankshaft;
• and a balancer disposed at a position farther from the cylinder bore than the idler gear and rotated by power transmitted from the idler gear, and
• wherein the lubrication system includes:
• a main gallery;
• and a balancer lubricating-oil passage branching off from the main gallery and reaching the balancer across the breather chamber in a plan view of the crankcase.