  Stellar collisions are an important formation channel for blue straggler
stars in globular and old open clusters. Hydrodynamical simulations have shown
that the remnants of such collisions are out of thermal equilibrium, are not
strongly mixed and can rotate very rapidly.
  Detailed evolution models of collision products are needed to interpret
observed blue straggler populations and to use them to probe the dynamical
history of a star cluster. We expand on previous studies by presenting an
efficient procedure to import the results of detailed collision simulations
into a fully implicit stellar evolution code. Our code is able to evolve
stellar collision products in a fairly robust manner and allows for a
systematic study of their evolution.
  Using our code we have constructed detailed models of the collisional blue
stragglers produced in the $N$-body simulation of M67 performed by Hurley
\emph{et al.} in 2005. We assume the collisions are head-on and thus ignore the
effects of rotation in this paper.
  Our detailed models are more luminous than normal stars of the same mass and
in the same stage of evolution, but cooler than homogeneously mixed versions of
the collision products. The increased luminosity and inefficient mixing
decrease the remaining main-sequence lifetimes of the collision products, which
are much shorter than predicted by the simple prescription commonly used in
$N$-body simulations.
