Play between the threads of the bolts and tapped hole is normal, until they approach proper torque. When a crankarm is insufficiently tightened and ridden loose, the steel spindle damages the tapered hole in the softer, aluminum crankarm. The most common damage is that the end of the spindle creates a burr in the hole. This is visible and often (about 80% of the time) careful filing of the burr will resolve the problem. However, the hole can also be distorted and this is usually visible to the naked eye only in extreme cases. Distorted holes are rarely repairable, except by a machine shop, and even then refinishing of the hole often results in the removal of enough material to cause the spindle end to protrude beyond the bolt seat. The bottom line is that cotterless crankarms that won't stay tight are generally scrap metal, unless there is a visible burr in the tapered hole.