Hybrid ceramic ball bearings use a combination of traditional stainless steel rings precision matched with silicon nitride (ceramic) balls. In addition to being excellent electric insulators, hybrid bearings have a higher speed capability and will provide longer service life than all-steel bearings in most applications.

I believe that the main issue is the change of design. Initially, Tong Sheng was using straight cut "big gears", and those were probably fine (in that "woblines" parameter), but at some point, somebody decided to use helical gears, to reduce the noise - and here lies the problem.Bearings are of standardised dimensions. In your case 6902 is 15 x 28 x 7 (inner diameter x outer diameter x width) and 6903 is 17 x 30 x 7 (which you probably got from Google). Calculation factor Y2:3.9; r1,2 min.:2.1 mm; b:11.1 mm; Basic dynamic load rating C:652 kN; Fatigue load limit Pu:73.5 kN; Calculation factor Y1:2.6; Basic static load rating C0:765 kN; K:6 mm; d3:155 mm; ra max.:2 mm; Size (mm):10 mm x 35 mm x 11 mm ;

Simply replacing the bearings with name brand ones won't help (apart from longevity). The majority of play isn't within the bearings themselves. There is some play within the sprag clutch but nothing can be done about that. Perhaps some retaining compound between the sprag clutch and big gear wouldn't be a bad idea. On mine it looks like there might be slight gap behind the spider where it could still potentially move. I currently have my motor apart and have been thinking how to improve things because I also had the chain ring wobble and rubbing over the pinion gear area. B1:121 mm; Calculation factor Y1:2; Ba min.:21 mm; Da max.:216 mm; Fatigue load limit Pu:104 kN; Basic static load rating C0:1060 kN; Mass bearing + sleeve:18.5 kg; D:230 mm; Reference speed:1900 r/min; Limiting speed:2600 r/min; Size (mm):60 mm x 130 mm x 31 mm ; ball bearings, roller bearings, thrust bearings, ceramic and ceramic hybrid bearings, stainless steel bearings, miniature bearings, linear bearings, shafting, corrosion resistant bearings - see the full listing in theWhen electrical current passes across bearings, a washboard pattern appears on the raceways, along with a darkened grey appearance. Typical results include bearing surface damage, premature aging of the lubricant. The natural insulating properties of ceramic material eliminates this type of damage. Basic Static Radial Load Rating Co:35500 N; Fillet Radius ra:1.00 mm; d:75.000 mm; Accessories:Without Accessories; Oil Speed Rating Open/Shielded n2:6700 rpm; D:115.0000 mm; Grease Speed Rating Open/Shielded n1:5600 rpm; Sealed Speed Rating n3:3400 rpm; Basic Dynamic Radial Load Rating C:42300 N; B:20.00 mm;

I read some posts before about replacing the sprag clutch, stating that I need a hydraulic press to remove the big gear, so I didn't expect it can move on the outer race. I replaced the sprag clutch also, and it turned out that I could press the gear in place using the vise - quite easily.Ceramic balls are only 40% as dense as steel balls, the centrifugal load that they generate is less and the internal bearing friction is lower. The lower density and friction enables cooler running under the same operating conditions, or even higher rotational speeds. D:130.0000 mm; Accessories:One Shield & Snap-Ri; Fillet Radius ra:2.00 mm; Sealed Speed Rating n3:3400 rpm; Oil Speed Rating n2:4500 rpm; Basic Dynamic Radial Load Rating C:134000 N; Basic Static Radial Load Rating Co:143000 N; B:54.00 mm; Grease Speed Rating n1:3400 rpm; d:60.000 mm; Accessories:Snap-Ring; Oil Speed Rating Open/Shielded n2:1700 rpm; Fillet Radius ra:3.00 mm; Basic Dynamic Radial Load Rating C:302000 N; D:420.0000 mm; Grease Speed Rating Open/Shielded n1:1400 rpm; d:280.000 mm; B:65.00 mm; Basic Static Radial Load Rating Co:405000 N; Sealed Speed Rating n3:890 rpm; Size (mm):2.953 Inch | 75 Millimeter x 6.299 Inch | 160 Millimeter x 1.457 Inch | 37 Millimeter ; b:7 mm; Grub (set) screw size:M6; B:15 mm; G:M 65x2; Associated spanner:HN 12-13; h:3 mm; Recommended grub screw tightening torque:8 N·m; d1:77.5 mm; B3:3 mm; d3:85 mm; According to the available data, this motor can produce somwhere around 90 Nm of torque, so I will use this number for calculation. Radius of the "big gear" is about 58 mm. To produce 90 Nm of torque, motor must provide about 1550 N (it is like weight of 158 kg!). So far, so good.