Sears Craftman Garage door opener model # 41a3493-1. Does it have auto reverse?

Without model numbers no one can possibly know.

The 'down limit' on the side of the motor housing is what needs to be adjusted. Turn this control in the opposite direction of the arrow printed on the cover. I usually adjust this so it stops short by quite a bit and then fine tune it.

What's the question?

If the main light flashes 10 times when the door reverses it is a door sensor problem. Make sure the sensors are pointed at one another and the small light on each one is lit and not flickering. Tweak them a bit.

If the main light flashes 10 times when the door reverses it is a door sensor problem. Make sure they are pointed at one another and the small light on each one is lit and not flickering. Tweak them a little. If you cannot get both lights to come on you have bad sensors or the wiring to them.

DID YOU REINSTALL THE LITTLE "CUP" ON THE MOTOR SHAFT.

IT MUST BE INSTALLED AND PUSHED UP SO THAT IT IS PICKED UP BY THE RPM SENSOR.

THIS WOULD GIVE YOU WHAT YOU DESCRIBE.

If the main light flashes 10 times when the door reverses it is a door sensor problem. Make sure they are pointed at one another and nothing is blocking them. Each one has a small light that will be one when they are pointed correctly. If you can't get both lights to come on you need new sensors.

If the main light is flashing 10 times when the door reverses it is a door sensor problem. One may have been bumped so that they no longer point at one another. Make sure the small light on each sensor is lit and not flickering. If this isn't the case you might need to increase the down force a little. The control is on the back panel near where all those white wires go. Increase it about 1/4 turn and try.

Sounds like the drive gear is stripped. Remove the cover and take a look. It is white nylon and is just in front of the motor.

If when it does this your main light flashes 10 times it is the door sensors. Make sure they are aligned properly. If the main light doesn't flash 10 times then you most likely have a bad RPM sensor board. It is a small printed circuit board just in front of the motor.