One of chain pulley for the garage door is broken. I need to replace it. See the image. The white round pulley is broken. I tried to touch it and felt it is very tight.

I ordered the part from amazon. But I worry that I may be hurt if replace it by myself.


  1. How to uninstall it?
  2. How to install a new one?
  3. Tools?


1 Answer 1


Loosen the tensioning screw the BIG SHINY BOLT - lower left side of the rail guide in the image you posted. BEFORE YOU LOOSEN it ... KEEP YOUR CHAIN IN POSITION. Put a nail through the slots from one end across the chain rail guide and tape it with duct tape or tie it - you could use a wire tie as well if you have one it is much easier.

There should be either a plate that your tensioning pulley is attached to via the bolt in the center of it - you should be able to unscrew it - keep in mind that it might be a left hand bolt AKA: LEFTY TIGHTY, RIGHTY LOOSEY - which is opposite of Standard Bolts which are called Right Hand - Righty Tighty, Lefty Loosey.

So to test for Left Hand Bolt try turning 1/8 turn to the right and see if it loosens. Or check the service manual.


Loosening the jacking screw will allow you to remove the chain from the pulley. At this point you should be able to remove the entire pulley with jacking screw ;which might make it easier for you to see how the pulley is assembled in order to remove it, or you can unscrew the pulley. See an edited picture of your picture.

Image with instructions pointing out items.

  • If there is a graph instruction; it would be helpful.
    – Love
    Apr 16, 2017 at 11:53
  • @Love I posted a picture with instructions and information. BE SURE TO UNPLUG THE GARAGE OPENER BEFORE DOING ANYTHING! - a running gear with fingers in the way turns into a meat grinder.. I have to state that because some people think hey it is off - or that only their opener will open their door. Some aircraft have actually triggered doors to open!
    – Ken
    Apr 17, 2017 at 16:46
  • I marked it as the answer, However, the bad news is the chain was broken before I was going to do any repair. Sadly.....
    – Love
    Apr 22, 2017 at 0:54
  • @Love go to a bicycle shop and ask for some replacement chain to fix yours with. They sell links and even master links - a hardware big box might also do the same - they are really easy to fix.
    – Ken
    Apr 23, 2017 at 19:29
  • I posted another thread at here.
    – Love
    Apr 24, 2017 at 12:14

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