rotate with the pump impeller 5 fig3 illustrates the impeller end of the drive shaft 6 which has been machined to receive the preloader device 8 the machining process is performed such that the preloader device 8 may be placed the desired distance from in front of the eye of the marine jet drive impeller thus for a drive shaft 6 having a first land 10 with a keyway 11 for receiving an impeller 5 and threaded 12 to receive a keeper nut and or spinner a second land 13 to receive the preloader device 8 is machined upstream from the first land 10 and a keyway 14 is machined to accept a key to secure the preloader device 8 to the drive shaft 6 the length of the second land 13 and its distance from the shoulder 15 of the first land 10 are determined by the depth of the preloader device 8 and the desired spacing upstream from the impeller 5 a distance of one inch between the preloader device 8 and the marine drive impeller 5 has been found effective however the distance between the two elements may vary according to the desired load or the space constraints of the marine jet drive housing if necessary a spacer 16 which fits in a snug fashion over the marine jet drive shaft 6 is used to keep the desired distance between the preloader device 8 and the impeller 5 when the machine work is complete the marine jet drive shaft 6 together with the preloader device 8 the key the spacer 16 if needed and the primary jet drive impeller 5 are installed into the jet drive unit and the nut not shown which originally.