INTERNAL COMBUSTION ENGINE

PROBLEM TO BE SOLVED: To provide an internal combustion engine including an endless transmission belt transmitting rotational power from a crankshaft and wound around a driven wheel and a drive gear engaged with a driven gear provided on at least one of a pair of cam shafts and provided coaxially with the driven wheel, capable of avoiding an increase in the distance between the paired cam shafts and achieving the size reduction of a cylinder head.SOLUTION: A driven wheel 90 and a drive gear 94 are disposed closer to a crankshaft 42 than a line L connecting central axes of a pair of cam shafts 77 and 79, a bearing wall constituting part of an inner wall of an accommodation chamber 104 formed in an engine body 29 is provided in a cylinder head 45 so as to include a pair of cam shaft slide contact support surfaces supporting and slidably contacting at least part of outer circumferences of the paired cam shafts 77 and 79, and a driven wheel accommodation recessed portion accommodating at least part of the driven wheel 90 disposed closer than the drive gear 94 to the bearing wall is formed in the bearing wall. 【課題】クランクシャフトからの回転動力を伝達する無端伝動帯が被動輪に巻き掛けられ、一対のカムシャフトの少なくとも一方に設けられる被動ギヤに噛合する駆動ギヤが被動輪に同軸に設けられる内燃機関において、一対のカムシャフト間の間隔増大を回避して、シリンダヘッドの小型化を可能とする。【解決手段】被動輪９０および駆動ギヤ９４が、一対のカムシャフト７７，７９の中心軸線間を結ぶ直線Ｌよりもクランクシャフト４２側に配置され、機関本体２９に形成される収容室１０４の一部の内壁を構成する軸受壁が、一対のカムシャフト７７，７９の外周の少なくとも一部に摺接して支持する一対のカムシャフト摺接支持面を有するようにしてシリンダヘッド４５に設けられ、駆動ギヤ９４よりも軸受壁側に配置される被動輪９０の少なくとも一部を収容する被動輪収容凹部が軸受壁に形成される。【選択図】 図２