Remember to not over-tighten the chain. Just tighten enough to stop it from hitting the rail.
Replacement gear kit if you need one→ http://amzn.to/2dRtDVc
If you need a kit, verify it is the right kit for your specific model garage door opener before you buy. In this video, I show you how to tighten a loose sagging chain on a Liftmaster Garage door.
Disclaimer:
This video is only for entertainment purposes. Any injury, damage, or loss that may result from improper use of tools, equipment, or from the information in this video is the sole responsibility of the viewer and is to be used at the discretion of the end user/viewer and not AdamDIY and or Adam Hill. If you are uncertain about any step of the process, or feel unsure about your skill level, seek a more authoritative source.