what makes mini quad motor hot? is it motor timing? ESC firmware?

Because on start of using my Emax motors, i remember they wasn't hot at all

Now they are pretty warm after 2 mins hover.

I set everything on default (Timing is medium.. never change that), and low PID values. and result is almost same.

Is possible the motors are just old ? I mean the bearings.

Old/damaged bearings become crunchy, if you don't hear any non-harmonic extraneous sound while the motors are running, they are fine.
Maybe your current ESC settings are just not the optimal ones for your motors, resulting in less efficiency and spreading more energy as heat. Try playing with timings.

If nothing helps, motors can be hot after flying aggressively, don't pay too much attention to it.

The only thing that would give more information I can think of is testing each motor on a thrust-bench individually, all while measuring RPM, current draw, thrust and bell/winding temperature.
I don't have a small multirotor at the moment, the motors of my big tricopter which had numerous crashes get significantly hot unless I replace bearings. But if it's cold outside, they're barely warm.

High D value in the PID will heat up motors , Put up you PIDs for us and we can give some advice. BetaFlight/cleanflight has upped the default , D value in YAW from 0 to 20 a few versions ago. Drop that to 10 and see if that makes a diferance. If the bearings are old you would notice noise more than heat as the bearings start to self destruct. A couple of drops of oil in 1 motor for a test is worth a try . Take props off, hook upto PC/cleanFlight/BetaFlight rev up the motor your going to oil , listen to that motor. Stop the motor, put in a couple of drops of oil in the 1 motor , test again and listen for a definate sound change, and prepare for the excess oil spray. Test fly the quad and see if there is a noticeable temperature differance in that motor compared to the others. I hope you find the solution , Lets us know what the outcome is .

What props are you using? My RS 2300KV don't like 5045

I've run into over heating issues with the Emax RS2205/2300 recently. I suggest checking a couple things.
1) check that the motor mount screws are not too long and touching the motor windings
2) try resetting the FC firmware back to defaults
3) gradually reducing the PID values. (This helped solve my particular issue)
4) check your props, I've noticed previously that using chewed up props can cause motors to heat up due to extremely vibrations.

Good luck!

Hello, i think i've a problem with my motors in my new built. They are getting hot when hovering(2 min with DAL 5040 3 blades)and on bench too in a couple of minutes when tryng to calibrate max thr)
Motors: racerstar rf 2205-2300 4s
Esc:racerstars ms35a blheli s flashed with latest FW available last week.
Fc:xracer f303 v3.1 8K/4K,Multishot unsyched 32000.
They are getting pretty hot just running on the bench for seconds just to find max pwm value on Betaflight and with propelles they are really hot just overing for a minute or two.
No screws are shortening windings on motors(checked with caliper)
With escs i've no problem of temperature,they are just a little warmer than room temp.
Please help!
Tia

Could be noise feedback caused by frame resonance, bad prop or motor balance. Or too high P/D.

Is fc softmounted? Filters adjusted? Can you log gyro data?

Do the motors get warm too on the bench when not armed (i.e. Transmitter off, only using the motor tab sliders, means PID loop is inactive)? Don't go full throttle, without prop load motors can go into a kind of self-oscillation...

One of my birds actually gets warm too at hover point (frame resonance), but when actually flying, throttle is above or below, so it doesn't matter much.

Adding a couple of orings on fc.thanks.
Tested with props temp is good even on bench.

But the situation is getting worse since i've noticed some motor STUTTERINGS(maybe on right side) when increasing throttle quickly, if done gently it does not stutter.
Now i'm checking the solderings but seems everything ok....

Plugged on Betaflight Motor tab and no stutter in all throttle range.Maybe not a solder/hardware problem?
But still on motor tab, instead of the master throttle slider i used tx throttle(obviously without props) and it stutters only when moving the quad with hands ,like when hovering with props on.It's even worse in Horizon mode than in Rate.Maybe a tuning problem?
May i attach a dump,please?
Ps .Esc Motor timing is set to default Medium High

Well, without props (and tx on) it will try to control but obviously can't... so don't interpret too much into it.

Real flight behaviour is more important. If it's fluttering/oscillating in a hover, you might try lowering P. If it's just noisy, maybe lower gyro lowpass filter a bit.

No it is not noisy or oscillating. It hovers pretty stable. When increasing throttle there are a couple of "cut off "(noisy like braking) of power very fast,a fraction of second in the right motor side.
But under constant or slow increase of throttle seems ok.