Variable valve timing system

A hydraulically controlled variable valve timing system to be mounted on an engine, the variable valve timing system comprising:

• a camshaft rotatably supported via a bearing surface formed in a support wall of the engine;
• a thrust stopper formed on an outer peripheral surface of the camshaft, the thrust stopper configured to set an axial positioning of the camshaft;
• a hydraulic variable valve device configured to selectively advance and retard a rotational position of the camshaft with respect to a crankshaft of the engine;
• and
• an oil control valve configured to control a hydraulic pressure of oil supplied to the variable valve device, wherein:
• the bearing surface includes:
• an advance groove through which the oil passes so as to advance the camshaft,
• a retard groove through which the oil passes so as to retard the camshaft, the retard groove positioned on a first wall surface side of the support wall, and
• an accommodation groove configured to accommodate the thrust stopper, the accommodation groove positioned on a second wall surface side of the support wall, and
• the advance groove is positioned between the retard groove and the accommodation groove such that a counter hydraulic pressure configured to suppress oil leakage from the advance groove is generated in the retard groove and the accommodation groove.