Chain ring loose

If a chain ring is wobbling on the crank arm spider, first check to see whether either the ring or the spider is cracked. If not, attempt to re-tighten the chain ring bolt.

Chain ring bolts normally have a 5mm Allen bolt on one side and a thin, flat nut on the other side with a slot in its edges. There’s a special tool for this nut, but it’s unlikely you’ll have one with you on the trail. To loosen or tighten this combination, you must jam a screwdriver or similar tool into the slot in the nut while turning the bolt side with an Allen wrench.

If one or more bolts are missing, attempt to redistribute the remaining bolts in a way that holds the chain ring in place. Typically, the large and middle chain rings are held with the same (longer) bolts while the granny chain ring has its own (shorter) bolts. For some versions of XTR, however, all three rings use the same bolt.

If the chain ring is cracked or loose enough that the chain will not stay on it, remove it entirely. You may need to create spacers for the bolts that hold the two larger rings on after removing one of these rings.

With a chain ring missing, shift the front derailleur only when the bike is stationary, and manually lift the chain between the remaining chain rings, or adjust the high/low screws on the derailleur to prevent the chain from moving into the space left by the missing ring.