Re: Q: Mounting 100+ lbs LCD to Drywall
The mounting plate should be plenty wide enough to span at least one stud bay (typically 16" centers ), if not two, which means you should be able to mount the bracket directly into studs. DO NOT attach to the drywall only, unless you want an expensive trash can weight in the form of your new TV lying in pieces on the floor.
When drilling pilot holes, choose a drill bit that is the diameter of the fastener shank (threaded portion sans the threads ). Say you have a 1/2" lag bolt. The height of the threads are 1/8" on both sides, which means the shank would be 1/4", you would then use a 1/4" drill bit for the pilot hole. This is just an example, the numbers are merely for explanation. In reality, the easiest way to size the pilot bit to the bolt is to hold the drill bit up to the bolt and select the bit that is the same size or just shy of the shank diameter. You want to just barely see the gullet of the threads (bottom of the valley between each thread ) on either side of the bit.
As was mentioned, you can use a small nail and tap it into the drywall to find your studs, and more importantly, find the center of those studs. Hold the mounting bracket on the wall where you want to place it. Mark it's width and the line where one of the mounting rails will be on the wall. Using a nail, probe the drywall along this area to find your studs, go about 3/4" spacing until you find a stud, then probe to find it's center, from there you can measure 16" to find the next stud, then nail probe to find center.
Once you find the stud, drill one pilot hole, set the mounting bracket, and start the bolt, then mark your other pilot hole locations. Take the bracket down, drill pilot holes, mount the bracket.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!