The v2 Bukobot has the X axis synchromesh cable in a different location than the v1, so if you want to put the v2 X carriage on your v1 you need special spacers to hold the cable in the correct position for the new carriage.
Two synchromesh cable spacers are needed, to hold the cable the correct height over the carriage plate. The upgrade kit may come with two laser-cut acrylic pieces to use as spacers. If you don't get those, print them and make sure they fit into the top carriage plate as shown below (a file and a rubber mallet may be handy).
For maximum strength, print these as solid pieces, without infill voids. In Slic3r, the Print Settings tab, the Infill section, Solid infill every: 1 layers.
If your v1 Bukobot is sufficiently different from this one for some reason, or if you're just generally paranoid, you can print this shimmable spacer instead. (Or print both kinds, just to be sure.) An M3 button-head screw goes down through the top part, through as many M3 washers as you need, then through the bottom part. A washer and nut goes underneath to hold it all together.
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