Oil cooled plus metal gears means for eventual metal shavings circulating from the gears. These metal shavings will be in contact with the stator and will collect on the neo magnets if that gear metal is ferrous.
@neptronix: I doubt that shavings get through the bearing into the motor. When disassembling the motor, it wasn't even filled with oil, while the outer part (between motor and hub) was filled with oil. The motor dind't run very long though, I can't exclude that oil could potentially get through the sun gear bearing
Let's try and see.. I agree that "oil cooling" and steel gearing geared outrunner hubs is somewhat senseless. But here we have an inrunner..
As i'm always keen to see new chinese products, i had to buy one and open + test. Not bad IMO, only really crappy thing is the finish.
Some measurement on this motor
Inductance: ~1000µH @400Hz
KV: around 57 (i have to measure again with better tool)
Resisance around 200-300mOhm (i have to measure again with better tool)
Magnets: 8 (max rpm with acceptable eddy current loss should be around 3750rpm)
rotor dia: ~63mm
stack thickness ~22mm
Clutch Type: ratcheting, 4 catches
lubrication: oil, seals on both sides
reduction ratio: 7
axle dia: 14mm
spokes flange dia: 137mm, 36 spokes
spokes flange distance: 40mm
6-hole disc interface: yes
weight: around 3.2kg
Noise: Less than the bafang BPM. Quite silent, but there is some resonance at ~7kph (26" rim)
any more info needed.. just ask