AIR-COOLED INTERNAL COMBUSTION ENGINE

摘要

PURPOSE: An air-cooled internal combustion engine is provided to improve air-cooling effect in a cooling air passage and to position an ignition plug at an easily detachable part. CONSTITUTION: An air-cooler internal combustion engine comprises a valve gear mechanism provided above a combustion chamber; a cooling air passage(32) extending in the fore-and-aft direction between the combustion chamber and the valve gear mechanism along an exhaust port(7) and an intake port(9); a laterally extending cooling air passage(35) disposed between the exhaust port and the intake port to communicate with the cooling air passage extending in the fore-and-aft direction; an ignition plug provided in the laterally extending cooling air passage; and a cooling fin curved from the cooling air passage extending in the fore-and-aft direction toward the laterally extending cooling air passage. A centerline(A) of the exhaust port is inclined with respect to the fore-and-aft direction of the internal combustion engine to broaden a front opening(33) of the cooling air passage extending in the fore-and-aft direction.