In an engine, like in movies, the cast assigns roles. Here, the actresses are our girlfriends, the valves. Controlled by the famous camshaft, they must open and close at a frenetic pace in order to ensure the intake of the air-fuel mixture and then the exhaust after explosion. This alternation must be perfectly coordinated with the back and forth of the pistons. This is precisely the role of the toothed timing belt. In the event of a breakage, it is the piston-valve shock and the destruction of the engine. Hence the need to respect replacement deadlines!