Chainring loose
 

Hello all, I am new here. So I was doing maintenance on my single speed cruiser bike and when I removed the drive side crank arm I just happened to notice that if I hold the crank arm with one hand and turn the Chainring with the other it seems to move a tiny bit, with a tiny click sound, I can turn it back and forward just ever so slightly. I assumed that the crank arm and Chainring were one piece but I guess not. Is this a major safety concern? I rode it earlier for about 25 miles with no problems. Can it actually completely break and separate from the crank arm? Or will it slowly get more loose without breakage? I just don't want it breaking on me while going uphill or downhill.

It sounds like you have a swaged crankset (see below) rather than one-piece forged. They do sometimes break loose, and though it most likely will continue to progress gradually, it should be replaced soon. If nothing else it will start causing the chainwheels to waver back and forth.

What type of crank? Many cruisers use one-piece "Ashtabula" type cranks, where the chainring is prevented from rotating by a pin on the back of the arm that fits a hole in the ring. If the drive side cone is slightly loose, the ring can move within the limits of the hole/pin.

It's unlikely to catastrophically fail, but fixing it will require removing the crank from the bike and tightening the cone against the ring to hold it firmly.