A loose stem on your bicycle isn't just annoying, it can also be dangerous. Stems sometimes become loose following a crash or after a rough ride over some rugged terrain. The stem is the part that keeps your steerer tube connected to your handlebars. Leaving a stem loose can cause the handlebars to shake while you're riding, which may lead to loss of control. Instead of ignoring that loose stem, you can usually fix it up quick yourself and be back out riding in no time.
Loosen the stem's pinch bolts. Threadless stems are secured to the steer tube with these bolts, that when squeezed can clamp them together. Then, find the bolt located inside the stem and loosen that too. Next, remove the stem from the steerer tube. Your steerer tube is the part attached to the forks of the bike, which hold the wheel axle.
Grease the stem with a thin coating of bicycle grease, which is a pasty lubricant that can be found at a bicycle shop. Then, place the stem back onto the steerer tube, replace the bolt inside the stem and tighten.
Align the stem by placing the front wheel between your feet and pointing the stem straight toward the top of the wheel.
Re-tighten the pinch bolts and test the handlebars to ensure they move freely.
Unscrew the top cap from the stem, which is located at the top of the stem, just above the steerer tube. Loosen your clamp bolts until you can pull the stem up from the steerer tube.
Apply a thin coat of bicycle grease to the stem and push back down onto the steerer tube.
Hold the wheel between your feet, while facing the back of the bike, and align the stem with the wheel.
Tighten the clamp bolts until they are snug, without over-tightening. Screw the top cap back on and turn the handlebars to make sure they are tight again, but still move freely.