Garage door chain isnt engaged. motor is running

did you check the manual pull up cable maybe in gauged

If motor continues to run but no chain action check for missing chain tooth or cam gear worn.

All garage door openers have a quick release. Have you checked to make sure that is locked in place? Most have a cord hangin from it and you pull it which releases it from the chain. Make sure that is engaged and it should work.

Pull down on the manual release rope. It may be hard to pull.

Use the emergency release handle to release the door. Run the opener to the open position until it stops. Close the door until it stops. Now re engage the the door.

You must ensure the drive chain is engaged to the door puller.
Sometimes the emergency release if pulled (red cord) the drive and the coupling come separated.
Make sure the pin is back in place (pull release cord and make sure pin springs back in).
The run an open close cycle, it should pick up the drive again.

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Many thanks

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If the motor is spinning but the chain is not, then there is probably a bad gear before the sprocket.
You need to decide the type of gear kit you need.

https://www.superiordoorparts.com/pm-134-12-liftmaster-chamberlain-garage-door-opener-gear-kit-41a2817.aspx

If the chain does not move but the motor runs then you have stripped the internal gears. I would replace here. These chain glide units are not very strong. There might be a chance the chain is telescoping down the rail but the trolley is not hooked up. Pull the red cord back toward the motor to engage. Thanks BB

The chain and bracket should automatically engage the door's bracket just use the remote as normal,

Make sure the rope hanging down has not been pulled. If it has the door has been disengaged from the opener. You can correct this by flipping the metal part up (that the rope is connectd to) toward the drive track. Then open or close the door using the remote. The track should grab the door again.