The tines of a Troy-Bilt rototiller should be inspected for wear once or twice a year. When tines are worn to a point, leaving a shape that resembles a hand sickle, they should be replaced. Worn tines will leave strips of untilled soil, because the ends of the tines no longer come close enough to almost touch. This is necessary if all the soil in the tiller's path is to get pulverized..
Buy the sets of Troy-Bilt rototiller tines you need from any of several retail and online sources, including the MTD Corporation, which owns the Troy-Bilt brand. Use the model number and serial number of your tiller to ensure you get the correct parts.
It may not be absolutely necessary, but when replacing tines many users choose to replace the locknuts and bolts that secure the tine holders in place, and all the nuts, lockwashers, and bolts that secure the tines to the holders.
Use two 9/16-inch wrenches to remove the locknuts and bolts on the tine holders, then slide the holders and tines off the shaft. The tines are mounted on a tine holder, one on each side of the tiller, which is secured to the drive shaft by a locknut and bolt. A 1/4-inch pin punch may be needed to drive the bolt out of the shaft. You will probably need to use a mallet to free the holder. If the tine holder has been in place for some years, it might have rusted in place and will require penetrating oil and/or heat to free it from the shaft.
Clean the shaft, transmission housing, and the inside of the tine holder thoroughly, right down to bare metal. Apply a high-quality grease to the tine shaft, and deburr the hole through the shaft if necessary. Check the oil seal for leaks, and replace the seals if needed.
Note the arrangement of the tines on the tine holders. A few digital photos will help with reassembly. Each tine is secured with two bolts, lockwashers, and nuts. Use two 9/16-inch wrenches to remove these, carefully setting them aside.
Install the new tines in the same arrangement, so that the sharp edge of the tines will enter the soil when they revolve. Replace the bolts, lockwashers and nuts, and tighten securely. Note that the heads of the bolts must face outwards!