Two-arm belt tensioner

In a belt drive (1) of an internal combustion engine (3), a two-arm belt tensioner (16) has a fixed tubular supporting portion (20); a first (24) and a second (23) arm fitted to the tubular supporting portion (20) to rotate about a common hinge axis (21), and supporting respective idle wheels (25)(26) cooperating with respective branches (12)(13) of the drive belt (11); and an elastic device (33) for forcing the arms (23)(24) towards each other; the elastic device (33) having a torsionally elastic elongated member (34) extending through the tubular supporting portion (20), coaxially with the hinge axis (21), and having respective opposite end portions (37) (38) projecting outwards of the tubular supporting portion (20); the end portions (37)(38) being fitted with respective end caps (40) (41), one of which is fitted directly with one of the arms (23)(24), and houses one end, connected integrally to the other cap, of the other arm.