I have Riva Eagle 2 SPD pedals on my MTB, and when I got them, the bearings were extremely stiff. I took them apart and loosened them up, and then rode on them. The problem is, the left-hand pedal bearing keeps tightening itself up. It becomes very stiff after 10 minutes or so of riding. I think the problem is that I can't get the lock-nut inside the pedal tight enough without tightening the cone as well. On most of the pedals I've worked on, there's a keyway on the axle and a keyed washer between the cone and locknut. These pedals don't seem to have that, which is probably why I can't tighten the locknut without moving the cone. It's only the left-hand pedal that does it, the right one is fine. Does anyone have any ideas as to how I might stop it happening?