GrumpyBear did a great job answering your questions, but I have a little bit to add.
I have a 2200kv motor with a 30 Amp ESC running on a 2200mah Lipo, which gets very quickly too hot. I thought it was something to do with the prop size / prop balance but having tried it
the prop and after just about 30 seconds the back end of the motor still gets quite hot, I´m a bit miffed as to what´s the deal is? is it a bareings or the ESC? perhaps the timing? what can it be? Grateful for any feedback thanks.
"Without the prop"
is the same as
"without any cooling",
no wonder it overheated.
At rated KV RPMs, your motor would have a short life. Motors are designed to have a load and be cooled, do not run a motor without a prop.
Is it the bearings?
If the shaft is not loose to the mount, and the bearings are free moving and quiet, they're fine.
or the ESC?
perhaps the timing?
The ESC timing being advanced too fast, can cause the motor to over heat.
what can it be?
The causes I see most are;
Too much prop (back off on the length and/or the pitch), or poor cooling for the motor.
Some more reading
Some ways to Managing the Heat.