LiftMaster Professional 3265 Sprocket Snapped Off

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Michigan Ray

New User
I have a LiftMaster Professional 3265 chain drive 1/2 HP that was installed back in 2006. It's been working great with the exception of the chain sagging quite a bit. Ended up snapping off the sprocket at the motor for some reason after performing the following steps below;

1) Released the door arm and performed the level / balance test. All great.

2) Adjusted the chain, leaving some slack in the middle just above the bottom of the T Rail. All great.

3) Performed an open/close test; The door opened and closed fully as before but, when it closed hitting the floor it automatically re-opened.

4) Down Limit adjustment; Turned the screw clockwise in 3/4" increments testing the door fully between each increment. After performing several of these increments, I couldn't get the door to work properly. The door cycle ended up stopping about 3" above the floor and only raising about 24" coming to a stop. I then turned the Down Limit screw counter-clockwise approx. 3/4" due to thinking I turned the screw too much. I never touched the Up Limit or Force Limit screws throughout this entire process. At this point, the door jerked and ended up snapping off the sprocket at the motor for some reason. I'm going to replace the sprocket assembly but, I have some concerns before moving forward.

1) Any idea of what caused the sprocket to snap off? Did turning the Down Limiter to far clockwise the cause?

2) Is there a factory starting point on the limit screws? For example, so many turns from one end or the other so I don't bust another sprocket?

Please keep in mind, it operated great before and I didn't touch the Up Limit screw or the Force Limit screws. I would sincerely appreciate any idea's and/or help so I don't end up snapping off another sprocket. Thanks. Ray
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