which are referred to herein collectively as drilling fluid if desired the drilling fluids can even be changed during drilling e g changing from air and or other gasses to water and or other liquids as the drilling fluid typically as discussed hereinafter the drilling fluid flows through the bottom hole assembly and is recirculated back up wellbore 106 outside of tubing string 104 accordingly tool 10 may if desired be continuously powered by continuously flowing recirculated drilling fluid flow as another feature fluid flow through the tool is never completely shut off thus fly wheels 36 and or timing wheel 70 are positioned such that if these wheels freeze up or otherwise fail then circulation through tool 10 is not lost moreover during operation fluid flow through tool 10 remains substantially constant this feature of the tool provides significant advantages for example if the drill string is still advancing then drilling might continue this feature causes less problems for drilling motors and turbines in bottom hole assembly 108 as well because circulation can be maintained the drilling string may be removed more easily and or the mud can be changed for pressure control and the like circulation is normally an important factor for keeping a well bore from being damaged and the present propulsion tool in a presently preferred embodiment is designed so that the tool does not shut off fluid flow through the drill string at any time moreover circulation fluid flow through tool is substantially constant in other words instantaneous velocity of fluid and or instantaneous amount of fluid flowing as compared to average velocity and or instantaneous amount of fluid flow through any particular cross section of the fluid flow path entering or leaving fly wheel 36 or timing.