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The AC compressor is there only because it houses the gear motor and a couple AAA batteries. The accessories are left off because I don't think they add very much to model, educationally or aesthetically. You can explain to someone how and alternator works better than showing them, while trying to explain how the insides of an engine work together is more difficult. There are still more things I want to add to this motor but most of them will just be solid pieces of printed plastic with no moving parts so they'll pretty much be just for looks. And yes, the 22RE uses a timing chain but being able to remove the head and see the valves and pistons was more important than being 100% accurate when creating this model.
I did however, plan on making a distributor that illuminated little LEDs in head at TDC, just like the old models engines that I wanted as a kid. One of the reasons I made this.
As for why I used bearings, because I wanted to. And I figured that if somebody is going to take the time to print this model they'll spend the $8 for all the bearings to have a nice smooth running machine. And the bearings actually give the crankshaft rigidity once its assembled and being able to clamp the main bearing caps over the main journals correct any "crookedness" in the crankshaft and allows it to rotate true and straight. Also, if I didn't use bearings, the slop required to eliminate friction on any bearing surface would be so great that it would be just like running a real engine with no bearings. There would be clicking and knocking of all kinds when rotating. Notice the sound in the Youtube video? You can only hear the electric motor and the pistons on the cylinder walls, the way it should. But yes, this can be made without bearings and I probably will upload a version at some point.
As for your comments, I welcome all constructive criticism. It's seems a though you can't do that now a days without getting somebody butt hurt. But you will never learn if you don't take the advice of others into consideration, especially those who know more than you.
And I agree with you completely, the market is literally flooded with 3D printers and anybody can buy one and start printing right away but the gap between being able to print something and being able to design something to be printed is the major short coming with 3D printer movement. There needs to be better resources for designing items at home for the average person with a 3D printer.