  During the mass-transfer phase in Algol systems, a large amount of mass and
angular momentum are accreted by the gainer star which can be accelerated up to
its critical Keplerian velocity. The fate of the gainer once it reaches this
critical value is unclear. We investigate the orbital and stellar spin
evolution in semi-detached binary systems, specifically for systems with
rapidly rotating accretors. Our aim is to better distinguish between the
different spin-down mechanisms proposed which can consistently explain the slow
rotation observed in Algols' final states and assess the degree of
non-conservatism due to the formation of a hotspot. We use our state-of-the-art
binary evolution code, Binstar, which incorporates a detailed treatment of the
orbital and stellar spin, including all torques due to mass transfer, the
interactions between a star and its accretion disc, tidal effects and magnetic
braking. We also present a new prescription for mass loss due to the formation
of a hotspot based on energy conservation. The coupling between the star and
the disc via the boundary layer prevents the gainer from exceeding the critical
rotation. Magnetic-field effects, although operating, are not the dominant
spin-down mechanism for sensible field strengths. Spin down owing to tides is
2-4 orders of magnitudes too weak to compensate the spinning-up torque due to
mass accretion. Moreover, we find that the final separation strongly depends on
the spin-down mechanism. The formation of a hotspot leads to a large event of
mass loss during the rapid phase of mass transfer. The degree of conservatism
strongly depends on the opacity of the impacted material. A statistical study
as well as new observational constraints are needed to find the optimal set of
parameters (magnetic-field strength, hotspot geometry,...) to reproduce Algol
evolutions.
