Go ahead and mount it off center and save yourself a headache.
Mounting a garage door opener off center.
Overhead opener drive types.
This type of garage door drive has a ceiling mounted system with a rail track and lift you maneuver using a chain belt or screw drive mechanism.
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Overhead garage door openers have traditionally been the most common popular option for homeowners.
You may need to duplicate this for an off center mount.
Attach the straps to the irons with hex head screws.
As you said run perforated angle iron from the center stile to the next stile over.
Some of the door openers especially commercial brands mount along side of the door on the wall and may work if you can find one that is cost effective.
If the door is properly balanced you should be able to locate the operator anywhere but always perpendicular to the door.
Bolt the angle irons to a rafter or rafters with lag screws.
Can an opener be offset from the center maybe a couple of feet.
Attach the straps to the power unit with the hardware provided.
The opener can be installed within 4 feet to the left or right of the door center if there is a torsion spring or center bearing plate in the way of the header bracket or door bracket area.
You can t solve you re problems with the same level of thinking that created the problems.
If your door has extension springs the opener must be installed in the center of the door.
Use one piece as near to the top as you.
To offset mount the opener arm to the door section.
You can be off center with the opener provided the door has a torsion spring which it sounds like yours does if your door was extension spring the kind when the spring stretch along the horizontal track then it wouldn t work properly.