Originally Posted by Cory

I think you may have a fundamental misunderstanding of how gears work.

If you have a gear set with two gears that have a given number of teeth each and you wish to replace one of them, you must come up with two new gears where the sum of the tooth counts of the two new gears are equal to the sum of the tooth counts of the first two gears. Otherwise you will end up with the wrong center to center distance and they will not mesh.