Ring Gears on Flywheels 
Numerous times I have thought I needed a new ring gear due to wear on the teeth where the starter drive engages the ring gear when starting. This is especially true on older cars that, have seen many miles. 

   My solution to the wear problem is to take the ring gear off the flywheel, flip it over, and replace it on the flywheel with the unworn side of the ring gear positioned on the side that the starter drive engages. I also rotate the ring gear slightly to a different spot on the flywheel if the flywheel is to be put back on the end of the crank in the same position as it came off. This is so the starter will not tend to engage in the same area it did before you reversed the ring gear. An engine tends to stop in two locations, on the flywheel, 180 degrees apart, when it is turned off.

   The procedure for removing the ring gear is to heat the gear all around it's circumference with a propane torch until it is hot enough to drive off of the flywheel with a brass drift. This is with the flywheel supported off the floor with a large diameter steel or cast iron pipe.  Something that will not collapse or break as you drive the ring gear off the flywheel.

   Make sure when heating the ring gear that you avoid getting the flywheel real hot. You want to expand the ring gear just enough to drive it off the flywheel. That means the flywheel needs to be much cooler than the ring gear. 

   The flywheel is then flipped over, after cooling, and can be placed on a flat surface where you can drive the ring gear back on after you have reheated it to expand it to have a larger diameter than the flywheel. Remember to flip the ring gear so that the starter drive engages the unworn side of the ring gear and rotate slightly to place the worn teeth in a different position on the flywheel. I've known people to even go so far as to place the flywheel, with the ring gear off, in a freezer for a hour or two. This is to shrink it down enough to where you can simply place the reheated ring gear in the groove on the flywheel without having to drive it on with a drift. 

   I've had good results with these procedures. However, there are two caveats; one is if the teeth on the ring gear are severely worn, the ring gear may not last, and two if you heat the ring gear until it is red hot it may change it's hardness and make it prone to faster wear. Also, be careful not to heat the fly wheel too hot and/or in one spot too hot, they can warp.

   If you don't feel comfortable doing this yourself, most automotive machine shops can do it at a reasonable cost.