A system for mounting a fuel injector to an engine casing with an aperture includes a fuel injector having a flange for mounting to the casing at the aperture. The flange allows it to pass through the aperture. An intermediate ring mediates the mounting of the flange to the casing at the aperture. The intermediate ring is inside the casing at the aperture and defines an opening from which the fuel injector extends into the engine with the flange positioned inward of the ring. The flange is dismountably sealed to an inner side of the ring, and the ring is dismountably sealed to an inner side of the casing to mount the fuel injector to the casing. On dismounting the flange from the ring, the fuel injector can be displaced to allow the ring, to be moved away from the aperture. The fuel injector can then be withdrawn.