DIY ebike engine failuire

Hello everyone, I am new here.
I made DIY ebike and engine overheated and failed after 40kilometers. And I want you to help me figure out what I did wrong.
Specs:
Battery: DIY 48volts, 13x6 18650cells
Engine: ZY1020GD, brushed DC 48V. Input 20.8A, output 1000W, rated 3000rpm
Controller: yk31, 30A, 1000w
Drivetrain: 28inch wheel (622x38), motor sprocket:11T, wheel sprocket: 80T, 25H chain.
And brake sensor, battery indicator, throttle.
I am attaching photos of bike and motor rotor.

I finished making the ebike yesterday. It only achieved speed of 35km/h on flats. The engine was hot, but you could touch it for a second, I didn't measure the temperature. I was worried about the engine but I checked and found out that engine heating is normal. There was also a weird smell, but I assumed that it was just some kind of factory residue.
Today, the engine failed after 10kilometers. It started to smoke lightly so I took it home and opened the engine. Rotor temperature was 175°C. Engine is broken now, there is continuity between armature stack and commutator bar.
I suspect that the gear ratio is wrong. But I calculated it for 50km/h. Drag force at that speed should be about 70N, and the engine note says it has 3.2Nm torque.
So, if you can help me please do.

Could be a factory defect in the wiring, nicked insulation during the winding process shorting two sections to the stator.

But more likely is gearing that is too high (tall), so the motor is unable to reach an RPM that allows current to drop to an acceptable level, for the speeds you were going with the load on the motor.

Keep in mine it's not uncommon for vendors to rate motor power on their ads as continuous when it's really only a peak power, unless you use some form of active cooling. If that's true of this motor, then it may not be able to do what you're after.

It's also not uncommon for cheap brushed controllers to not actually limit current correctly (or at all), and this can damage motors and controllers.

However, you've got a 30A controller on a 20A motor, so the most likely thing is the loads you're placing on the motor are drawing so much current that it just overheated and burned out.

If you have a wattmeter, use that while riding to get an idea of what kind of currents and power you're putting thru it in various situaitons, and that will help tell you what kind of load it sees. May help you determine if it's gearing, or just not enough power capability to do what you want.

31mph (50kph) will probably take closer to 1200-1500w motor input to maintain, on a flat road. In headwinds, or up a hill, it'll take more. (1400w-2kw at the battery)

Thanks for your reply.
There are 9t and 92t sporckets available. I can gear it down to 43, 41, or 36 km/h instead of 50km/h. What is the best choice?
And the motor rotor needs rewinding. Sticker on it says 20.8A input, 48V. Output: 1000W so there is an error or a lie. I was surprised it didn't have any internal fan. Just holes on each side. So I also need to add 48v fan to cool it.
I just wanted to make cheap ebike.
I don't know if it wouldn't be better to fix the motor and sell everything except battery and buy 1,5kW front hub kit.

I would buy a hub kit if I were you.