How do you install a flywheel ring gear on a 1948 Ford 8n?

First, it is best to remove the flywheel from the tractor, to perform the work. If the old/damged ring gear needs to be removed, use a hacksaw and cut the old ring gear between the teeth, stopping just short of cutting all the way through. Next, use a chisel to split the gear. It can easily be removed by hand, once it has been split.

Use a wirebrush and/or sandpaper to clean the surface where the old ring gear rested on the flywheel. Remove any surface rust or burs, and smooth the surface.

Put some leather gloves on, hold the ring with a pair of visegrips or large channel-lock pliers, and heat the new ring gear evenly with a propane torch. Keep the flame moving constantly, and continuously around the ring. The ring gear will expand as it is heated, and grow larger in diameter as it gets hot. Check the ring gear against the flywheel frequently, to determine if it has been heated sufficiently to slip onto the flywheel. Once the gear is expanded enough to slip onto the flywheel, you must act quickly to position it exactly where it needs to rest. Hold it in place as it cools, making sure that it remains in the correct position. The ring gear will contract as it cools, and become permanently lodged on the flywheel in a matter of seconds. Allow the items to cool for a few minutes, and reinstall on the tractor's crankshaft when it can be handled without gloves. Always use a torque-wrench, and tighten the flywheel bolts in a "star pattern" in 10lb increments, until the manufacturer's recommended torque is reached. Double check all of the bolts once more, to verify their torque, and you are done.