If you replace the sprocket assembly in your chain drive garage door opener yourself, you may be able to save a lot of money. The process isn't as hard as you may think, so consider the guide below.
Step 1 - Turn off the Power
Disconnect the power cord from your door opener before doing any kind of repair.
Step 2 - Disconnect the Door
Disconnect the actual door from the trolley by pulling the red rope, otherwise known as the disconnect rope. You will then need to close the garage door by hand. It is important that the garage door is completely closed before doing anything else. Take a vise grip or some sort of clamp and place it on the rollers so that no one can open the door while you are working on the garage door opener.
Step 3 - Check the Chain
Make sure that the chain is released of any tension. You can do this by making sure the tension nut is adjusted. Use the 1/2 inch wrench to loosen the nut.
Step 4 - Remove the Retainer Cap
Take off the sprocket retainer cap. A clip is usually on the back of the cap. Just press on the clip and it should release easily. It is a good idea to make a mark where the position of the chain is in conjunction with the sprocket. You should do this before you remove it.
Step 5 - Remove the Chain
Now remove the chain from its position on the sprocket. Put duct tape on your chain to keep it from falling onto the floor. This also keeps it from getting tangled and dirty.
Step 6 - Remove the Housing
Now you need to remove both of the end covers and the housing. These covers are held on with 3 or 4 1/2 inch head screws that you can remove with a 1/4 inch inch socket. Make sure to unplug the wire goes to the garage door's circuit board.
Step 7 - Remove the Accessories
Remove the retaining clip and drive gear. Make sure to also remove the limit switch assembly. You can do this by squeezing the sides which are just under the bracket located by the drive gears. Don't make any kind of adjustments to the screws that are on the limit assembly. Take the RPM sensor off by simply unplugging its wire harness and then removing the RPM sensor from its securing tabs.
Step 8 - Disconnect the Wires
You are now ready to disconnect the wires that go to the garage doors motor. The wires are red, blue and white. Make sure to remember where the wires go. Always match the color wire to the same color terminal that it came from.
Step 9 - Remove the Motor
Remove the hex head screws on the motor. Make sure to hold onto the motor before you try to remove it. Slide the motor off and put in a safe place.
Step 10 - Work with the Sprocket Assembly
There should be 3 nuts holding the sprocket assembly. Simply remove those for replacement. If it is just a gear you are replacing, you should remove it after you have unbolted assembly and replace it with a new one by going in reverse order. If it is the entire assembly you need, just replace the assembly with your new one. When you're done with that, you can start putting everything back in the opposite order you took it apart.
Step 11 - Test Your Work
Once all is put back together, plug in the power cord and test the garage door opener to ensure that everything was installed correctly.