I was printing large objects, weighing about a pound and taking three days to print. I was getting a bearing knock when the carriage moved left to right. After the print I replaced all of the flange bearings and put another print on. Sure enough I got the same knock. I knew now it was the linear bearings in the print head. I applied 30w oil to the 6mm rods, but of course the oil just got wiped off and the knock continued. I then applied thick black wheel bearing grease to the 6mm rods. In half an hour the knock was gone and has stayed gone. I don't know if the balls within the bearing are frozen and the grease lets them be quietly dragged across the rods or if the grease just worked it's way in and they are circulating now. In any event the R2 is plugging along quietly. Well after not too long my prints went to hell. First I changed the hotend, and not the problem. I then felt the print head and it was verrry loose. I just installed THK LM6LUU purchased from Partsbuilt. Feels nice and tight now. Will follow up with print quality. Runs well no bearing knock and no play in the head. Can't say I see much improvement in print quality. What I do see is: on the initial layer feathering of the lines is much less. The print head no longer is pushed by the deposited filament. I use excess flow on the first layer to improve adhesion.