Rebuilding a window with sash weights is a pretty simple process. Many times the home may have historical value so the window styles must be maintained or there is no replacement window available that exactly matches. Here are some suggestions.
Windows with sash weights were common for many years and only in the last forty years or so have vinyl or wood windows with spring balances become common. Sash weight windows usually have single pane glass making them very inefficient against heat loss as well. Years of operation has caused wear of the wood tracks and the sash themselves causing even more air leakage.
Start by carefully removing the inside window trims if they are to be reused later. Carefully prying the trim off the finish nails and then removing the nails, helps prevent damage to the trim surfaces from hammers and pry bars.
Never pry directly against the trim itself. If you must pry on the trim face, place a piece of wood under the hammer claw or pry bar to avoid direct pressure on the wood. If new trims are to be installed, simply discard the old trims unless they can be recycled elsewhere in the home or maybe Habitat.
Once the all trims are removed look carefully in the window track slot at the bottom with the sash in the up position. You will see on each side of the window a small door recessed into the track slot itself, held in place with two large slotted screws.
The screws may be obscured by years of painting but careful scraping will reveal an indent where the screws are countersunk. Carefully remove the screws and then gently pry out the wood door piece on each side. Grasp the inner sash firmly and give a tug on one side to pull the sash out of the window frame. There will be a rope on each side of the window connected to the top of the sash as well to an iron weight concealed behind the window track.
Carefully and with a firm grip on both the sash and the window cord, twist the knot out of the window top. The window will come free. I repeat have a firm grip on the sash cord. The weight is much heavier than you think and will want to crash down into the window pocket if released. Slowly raise the sash cord until the knot comes into contact with the recessed pulley at the window top.
Repeat the process for the opposite side. Set the sash aside making sure you know which is the top and the bottom sash. Place a wood block into the track opening and cut the card knot. The block will help catch the sash weight and allow you to pull it out of the pocket. Remove the pulleys. The pulleys and the weights will no longer be used.
You will next see what is called a parting bead which is a small trim piece about 1/2 inch by 3/4 inch in size partially buried in the window casing. It separates the two sashes. I recommend replacing these and you will find they are very difficult to remove without splintering them. If you are repairing the window and not installing new side tracks you must replace the parting beads.
The upper sash and weight removal is the same as the bottom. Don’t forget to open the sash pockets at the bottom of the upper sash tracks as well to allow sash weight removals. With sash, weights, nails and pulleys removed, clean all loose paint from remaining surfaces and if your sure it is not lead paint, some sanding may be in order as well.
Your choices here become varied on how your going to repair the windows. Using loose fiberglass insulation or non-expanding foam sealant (do not use expanding type foam. It will bow the window frame and ruin it) fill all the voids left in the sash weight pockets. Push insulation down into the opening and up as high as you can.
Purchase a set of vinyl or metal side window tracks appropriate for your window size. Carefully measure for length and take notice that the ends are tapered on a slant, and are not a square cut. These slant cuts will match the sill slant. Slide one track into place and check for proper fit. Fasten securely following the manufacturers directions.
I always apply two thin lines of silicone caulking behind the track from top to bottom to assure there are no air leaks. The sash themselves should be re-glazed with new window points and window putty. Replace all cracked glass as well. Old putty although it may look sound may have shrunk away from the glass surface allowing drafts to penetrate alongside the glass.
Give the sash a new coat of paint making sure to prime all the bare wood first. There are available today high quality clear Lucite non-yellowing panels that can be cut to fit inside the sash edges in front of the glass. You should use a router to recess these pieces into the frame making them almost disappear. It becomes an inside storm window and is worth the effort.
With both sashes completed you must place both sash into the already installed track in their proper relationship. The parting bead is built into the track. Now with a helper, place the second track around the sides of the two sash and gently slide the assembly into the window opening.
Fasten the track into place. Place a fine bead of caulk on the inside of the track to seal it. Do not put so much caulk as to interfere with the trim replacements.
Pre-made tracks have screw adjustments in them to compress the spring inside thereby putting pressure against the sides of the sash. By trial and error you will find the best adjustment to allow free sliding of the sash but also enough pressure to hold the sash up when in the open position. You do not want them to come crashing down on a neck or fingers. Replace all the window trims and you will have not only a nice looking window unit but one that is free of drafts and is easy to operate.