This paper deals with a repair shop with multiple parallel servers, which has to carry out planned overhauls. Each overhaul consists of a large number of maintenance jobs. The overhaul process is interrupted by randomly arriving emergency jobs. To control the delivery performance of the overhauls, knowledge about the overhaul makespan distribution should be available. Using a 2-dimensional Markov model, we derive the first and second moment of the overhaul makespan analytically for the case that the repair times of all overhaul jobs are identically and exponentially distributed. For the case of nonidentical repair time distributions, an approximation is presented. Simulation shows that the makespan distribution fitted on these moments gives an excellent approximation.