UPDATE 3 (regarding Wanhao Duplicator i3/i3Plus):
I can only recommend removing the bearing rods and abundantly grease the inside radius of the original linear ball bearings with MoS2 grease, and remounting the bearing rods again with the greased original linear ball bearings. I have tried more than one type of printed bushings and they are not up to par with the original linear ball bearings when the original linear ball bearings are greased properly. The greased linear ball bearings are quiet enough and has lower friction than printed bushings. I have had friction based vibrations with printed bushings in conjunction with higher transport speeds. The greased original linear ball bearings shows no such issues.

UPDATE 2:
Well that did not last long! The bushings has become to snug after a week of use. I have now replaced them with the original linear ball bearings and they seem to have lost that terrible noise after I greased them and re-aligned them. So until further notice I can not recommend anyone using my bushings. I do not know why they has become to snug, and I don't care to find out either. I am sure I can re-heat the rods as described below and refit the bushings again, but there are other proven bushings to choose from. And of course to grease and re-align the original linear ball bearings that came mounted on the machine to begin with.
THERE ARE BETTER BUSHINGS OUT THERE THAN THESE!

ALTOUGH, they might be used as linear bearing rod fittings in one form or another (as is, without heat-fit). Feel free to experiment and build upon them.

I made these bushings to replace the original linear ball bearings that came with my Wanhao Duplicator i3 Plus. They were very noisy although the print quality did not seem to be affected when brand new. But I did not want to ruin the bearing rod by continuing to use them. And they were noisy!

I made my new bushings with a very tight fit, hard even, they cannot be used as is, they have to be prepared for use before mounted on the 3D-printer.

1. Remove the y-axis bearing rods and apply a thin film of grease to them.
2. Boil some water and dip one end of the bearing rod into the boiling water, let the water heat the end (5-7 cm) of the bearing rod for 30-60 seconds.
3. When the end of the bearing rod is boiling hot, take it out of the boiling water and press one of the printed bushings onto the rod. DO NOT PUT IT BACK INTO THE BOILING WATER!
4. Leave the bushing to sit on the hot end for up to a minute while gently rocking the bushing back and forth on the hot end twisting it a little.
5. When you feel it is enough, push the bushing to the bearing rods cool end to feel if the bushing runs smooth without any resistance or play. If it feels okay then you are done!
6. Repeat the procedure for each bushing. Pair the rods to each bushing respectively, the short bushings to one rod, change rod and pair it to the long bushing.
7. Let everything cool down and see if all bushings still runs smooth without play, if a bushing still feels to snug then repeat the process one more time.
8. Remount everything on your printer, align before tighten any screws. A good tip is to tighten everything loose at first, then go back and check alignment before continue with the next round of tightening them a little bit more, and check alignment, etc. check alignment again, continue until all screws are tightly secured and everything is aligned. If you begin tighten each screw hard from the beginning, things can get misaligned. Gentle steps does it!

Good luck! :)

Update:
-I have been using them for a while now and they seem to work just fine. Just be sure to have a thin layer of grease on the rods for lowest friction. They are quiet, smooth and without play.
If friction is an issue the rods should feel a bit warm to the touch after a long and fast print and of course the print quality would be affected. I have so far seen no evidence of any of this and I have been printing several hours of continuous fast printing without any apparent heat build-up on the rods. The question that remains is longevity, how long do they last? I have no answer yet.

I will update this text with the bushings life expectancy when I feel the need to replace them first time because of wear.

It would be interesting to know what you, other makers, think of them. :)