Using your drill, add tension to the torsion spring. This system uses a single spring for a double door, but many manufacturers use two springs for a double door. The painted line on the spring acts as a gauge for the number of turns you put on the spring. To keep the bar from turning while you’re adding tension, attach a locking pliers to the bar on both ends of the spring. Apply lubricant for garage doors to the spring.
Although the door weight and drum size determine the maximum torque (termed MIP, maximum inch-pounds) needed from the fully-wound spring(s), the spring selection for a given door can still be varied to adjust the cycling stresses. A heavier wire on a larger diameter or longer length will produce the same torque as a lighter wire on a smaller diameter or shorter length, while undergoing less stress and therefore increasing expected cycle lifetime. The heavier spring will cost more but last longer, so this is another design trade-off. Calculating these spring sizes in the field is done using a book of tables (or the software equivalent) that we cannot provide here, although you will find the formulas to estimate spring properties below. If you can accurately provide the weight of the door, or the size(s) of the old spring(s) (assuming they were well-matched to balance the door), then a spring dealer should be able to tell you which spring sizes will work for you.
All measurements should be in feet and inches. Step 1, measure across the existing door or desired space for the width, then up and down for the height. The rough opening of your space should be the same size as the door. Step 2, measure the sideroom, which is the space beside your door. Measure the width of the left side, and then the width of the right side. Step 3, measure the space above the door, which is called the headroom. Measure the height of the distance between the top of the door opening and the ceiling. Step 4, measure the ceiling, which is called the backroom. You’ll need to measure the distance of the garage door opening toward the back wall of your garage. You should have 6 total measurements in all once you’ve finished measuring the space. Keep in mind that having an automatic garage door opener installed might call for additional backroom or ceiling space.
You might genuinely need some extra parts when you thought you simply needed a broken spring replaced, and a good serviceman will perform a simple inspection to identify such parts. Nor is it unreasonable for a business to charge separately for a service call versus repair work actually performed. But the best protection for you as a buyer, being somewhat at the mercy of whomever you decide to bring on site, is to understand what is being done, and ask intelligently for a clear explanation or demonstration of why extra parts are required.