Summary

I modified InfinityPlusPlus' MK8 drive to use a simple to acquire "Delta Faucet" spring and optimized the placement of the vias to allow the extruder to drive either 3mm or 1.75mm filament. It also includes recessed heads for the 3mm attachment screws.

Instructions

1) Print both peices (optionally mirror the drive.)
2) Mount back to stepper with one screw in left hole (or right hole for left side extruders)
Note: Step #2 is optional... it works fine without this screw on most steppers due to the design being braced by the raised center portion of the stepper motor.
3) Remove spindle tower from inner portion of the bearing pressure arm.
4) Insert 623 bearing into slot and use 3mmx10mm screw from back to affix bearing. Make sure it turns freely. Trim if necessary.
5) Place arm on stepper with 3mm screw and insert spring.
a) For 3mm filament drive... use spring with small portion facing down.
b) For 1.75mm filament drive... use spring with rubber cap on small end facing up.
6) Tighten hinge screw to chassis.

Install as normal MK7 and start printing!

(BTW... the Delta Spring I purchased from Home Depot... here is a quick link to it: http://www.homedepot.com/h_d1/N-5yc1v/R-100169417/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=delta+faucet+spring&storeId=10051)

Minimalist MK8 Rework