Alright, so I'm new to this biking thing and just purchased a used road 2009 Giant Defy 3 that has about 500 miles on it. I took it apart to clean it and after taking off the front wheel, I noticed that it does not spin smoothly, I could feel a lot of catching/grittiness as I spun the wheel in my hands. I took the hub assembly apart and noticed that a few of the ball bearings actually have grooves in them. So I plan on replacing the ball bearings, do I need to replace the cones as well? Is there anything else I need to check out with this problem? I'm hoping they were just bad ball bearings as I can't imagine anything actually making grooves in the bearings, or am I wrong? Thanks in advance!
It's suspicious I'd say that with only 500 miles all up, that you should be able to feel any wear in the front hub bearings.
Clearly you can see damage to the balls & normally you'd also expect at least damage to the inner race (IE the cones). I'd guess there may be minor damage to the outer race also.
The problem is the difficulty in seeing the wear affected zone which you must clean thoroughly & then inspect minutely with a magnifying glass.
One trick I have read is: probe the wear zone with a disposable ball point pen, use the small ball point to feel for pits or roughness.
If you feel any roughness that's too much, because wear always develops rapidly from such areas.
BTW count the balls to see you you have the correct number on each side, it's just possible the previous owner did a hasty reassembly & lost a ball.
When you reassemble don't over tighten, you should always just be able to detect play.