  The low mass X-ray binary (LMXB) associated with the M31 globular cluster Bo
158 is known to exhibit intensity dips on a ~2.78 hr period. This is due to
obscuration of the X-ray source on the orbital period by material on the outer
edge of the accretion disc. However, the depth of dipping varied from <10% to
\~83% in three archival XMM-Newton observations of Bo 158. Previous work
suggested that the dip depth was anticorrelated with the X-ray luminosity.
However, we present results from three new XMM-Newton observations that suggest
that the evolution of dipping is instead due to precession of the accretion
disc. Such precession is expected in neutron star LMXBs with mass ratios <0.3
(i.e. with orbital periods <4 hr), such as the Galactic dipping LMXB 4U
1916-053. We simulated the accretion disc of Bo 158 using cutting-edge 3D
smoothed particle hydrodynamics (SPH), and using the observed parameters. Our
results show disc variability on two time-scales. The disc precesses in a
prograde direction on a period of 81+/-3 hr. Also, a radiatively-driven disc
warp is present in the inner disc, which undergoes retrograde precesson on a
\~31 hr period. From the system geometry, we conclude that the dipping
evolution is driven by the disc precession. Hence we predict that the dipping
behaviour repeats on a ~81 hr cycle.
