To remove a pinion that's been loctited on, you can buy special tools -- a pinion puller -- to remove them (it's a small version of a gear puller that you might use when working on cars).
Of course, if you used loctite to lock the pinion in place, heat is also your friend. Heat the end of the shaft, pull the gear off. Don't go overboard on the heat, however.
Example of a pinion pulling tool:http://www.fxaeromodels.com/product...roducts_id=1640
Can't help you with the pinion sizing question yet, my 250 is waiting for servos and a decent 0.9mm hex wrench to appear via UPS and USPS.
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