i have a few that i use constantly. two of them i got motors from dan kubin and put in, also i punched out the a-bar pin and put a shim washer on either side of the a-bar at the bottom, and superglued (!) shim steel pieces onto the parts of the frame at the top where the a-bar passes thru, thus eliminating the "rattle'' they seem afflicted by...tightened them right up but with no binding either. also i cut off the useless steel bars on either side of the crank, and had real vices made for them. considering i got the machines for free from a disgusted co-worker, and only spent on dans motors (vices were a tattoo trade from a buddy at a machine shop) , the difference is amazing. a third one has the same improvements, but with a 5mm crank. which lines with big groupings like a fat sharpie. the 4mm is now my favorite liner, and i swear the 3mm is my favorite tattoo machine for black and grey or portraits ive ever used. i dunno if the motors i got from dan are mabuchi, but they definitely run WAAAY smoother and a bit faster. the 5mm seems to like the o.g. stealth motor better.