Terrible, are the instructions that came with my Chamberlain LiftMaster Professional garage door opener 1355C, 1/2 hp. Sure, read them, but if you have no clue then try my rough adjustment guideline as a start.
My idler bolt broke, sending my chain flopping down. When I replaced my idler bolt, I had no idea how to get the chain adjusted. Firstly, close your opener. The trolley should be close to your door. put some slack in your chain and then route it through the opener’s gear. Then tighten everything up. Damn there’s nothing about this in the manual. I had to do this by trial and error three times, slackening, getting it into the gears, tightening, repeat 3 times. What a hassle. Clearer instructions would have been a time and frustration saver.
