When the teeth of the flywheel are damaged, the entire assembly of the flywheel should be exchanged. A ring gear can be installed instead of a flywheel, provided you use proper steps to protect the engine. Make sure to scribe on the flywheel to mark the place where the old gear was located, as a reference for alignment. Cut nearly all the way through the old part with the abrasive wheel and then remove the rest with a cold chisel or punch. To put the ring gear onto the flywheel, you need to warm it and stretch it because it's a close fit. Prevent damage by carefully heating your replacement gear by placing it in an oven and reaching a temperature of almost 375°F. Do not use an oxy/acetylene torch, as it can cause local heating that results in uneven gear expansion and wears the gear fast. Be sure to put on safety goggles or glasses and heat-protected gloves when you work with a hot ring gear. Always install heaters so they are even to stop anything from becoming misaligned or distorted; use a shop press and the proper press plates for this purpose. With the flywheel installed, lift it to a workbench and let the ring gear fully cool in normal air before you install the flywheel on the engine. Do not cool your new gear with water or blasts of compressed air, as you may break or warp the components.