62 on spring 24 spring spacers 60 pass through top plate 58 and are secured by nuts 64 first and second retainer plates 66 may be used to secure cassette 26 to housing 36 for example first and second retainer plates 66 may be positioned on top plate 58 by studs 68 and secured to bottom plate 56 by bolts 70 retainer plates 66 may extend radially beyond the edges of top plate 58 to engage an annular groove or slots formed in sprocket housing 36 thereby axially positioning and locking cassette 26 in place on hub 20 such that the inner tang 72 of spring 24 engages one of two alternate detents 74 formed in hub 20 retainer plates 66 exemplarily demonstrate only one arrangement for attaching cassette 26 to evcp 10 obviously all other alternative attaching arrangements are fully comprehended by the invention in the event of an emotor malfunction spring 24 is biased to back drive harmonic gear drive unit 12 without help from emotor 14 to a rotational position of second spline 30 wherein engine 18 will start or run which position may be at one of the extreme ends of the range of authority or in one aspect of the invention intermediate of the phaser 39 s extreme ends of its rotational range of authority.