Summary

I really did not want to cut the plastic on the top of the replicator2 extruder. So I made this derivative of the mk8 minimalistic.

Instructions

I have added 2 front version 3 files. The back piece is still on version 2. The first version 3 front piece has had the bearing slot opened up to allow up to a 10mm diameter bearing inside, and I have tested a 10mm bearing, works great. I have also put 2 cutouts in, the one on the back side to help with friction interference, and the one on the top to eliminate hitting the cover when no filament was in the printer, depending on your bearing size.

The second file I have also remove a bit of material from the front where the bearing contacts the drive, to accommodate an 8mm bearing, untested. Anyone who tries the different bearing sizes let me know if this helps or not.

Download the version 2 or 3 files. Print at 100 percent infill. I printed at .25 layer height.

Seems to be working great now and it has made my prints so much better than the stock plunger.

I have gotten all the holes to line up correctly now in version 2 and there is very little after print work. Cut out the bearing slot support, Install your bearing(I used a longer set screw). Bolt on as shown in the picture. Install your spring and put your printer all back together. Be careful not to over tighten the screw in the top left corner, it needs to take out the slack but too tight can cause it to bind and not allow the spring to do its job. Very similar to what you see in previous extruder mods, except you don't need to cut the plastic on a REP2 with this one.

I am still looking into an easier way to make the bearing support post, it is a bit hard to remove but nothing a small utility knife couldn't handle.

I used:
3x9x4 or 3x10x4 bearing . the 3x8x4 bearing front piece has not been tested by me.
one flat head m3 x 10 .5 bolt for the back right side
Re purposed the original bolt for the left side
m3 x 10 .5 set screw for bearing
1-3/8 by 23/64 spring from a cheap spring assortment I bought. Here is the link to the assortment I got my spring from. The spring tension is touchy because of the compact nature reducing leverage. This spring from this kit has worked great for me as long as your pieces are not binding and moving freely.
http://www.harborfreight.com/200-piece-assorted-spring-set-67562.html

I have heard concern over the back piece having issues with heat at the base because of the PLA. I have not seen any warping or failure and I put it through the ringer.

Mk8 upgrade without cutting for REP 2