The utility model discloses an engine pre -installation frock, it includes base, preceding supporting mechanism and back supporting mechanism, preceding supporting mechanism includes a support main part and a supporting beam, supports main part and base fixed connection, props up a supporting beam and includes longeron and sleeve, a supporting beam and sleeve sliding connection, sleeve and supportmain part sliding connection, back supporting mechanism and base fixed connection. The utility model provides an engine pre -installation frock can be through making longeron and sleeve relative slip, realize to the engine Z to the regulation of bearing height, and through making the sleeve and supporting the bulk phase to sliding, can realize the position control of longeron supporting mechanismafter for to the engine that can satisfy different dimensions supports, has realized the commonality.