You ask we answer. Here's the latest in our "Ask a Mechanic" series.
Q: Why do my sprocket bolts always come loose?
A: Because you didn't tighten them.
Oh, you were looking for more? OK, it is a common problem for riders but one easily solved. To actually answer your question, the sprocket bolts come loose because of all the energy being dispersed by the sprocket. Every time you roll the throttle the sprockets spin fast, then slow than fast again and sometimes just open up anytime you hit a straightaway. Add all that jostling from the ground, jumps and whoops you have a recipe for loosening that which needs to stay fastened. Eventually, the tightest of tights on these little bolts comes undone.
Therefore, before every ride - EVERY RIDE - tighten to spec. Get your torque wrench and tighten. Most likely you won't budge them one iota but that's the point. You have probably heard the phrase "give someone an inch and they take a mile" in some phraseology or another. Same thing applies to sprocket bolts. Once one gets a little loose it won't stay there for long and quickly unravels.
Also, just in case you forget to check the bolts before EVERY RIDE, and we know you will, fasten the bolts in using Loctite. That should keep them lock tight for a while.