ORIGINAL: Bass1
I'm pretty sure that karbonite gears and vibrating "gas engines" are a serious no-no[X(]. The 645mg servos are the way to go if you're on a tight budget. I would pull those "karbonite" geared servos out of your other gas planes YESTERDAY and install them in your glow or electric planes preferably under 12lbs. for safety. I have a set in a .46 size profile and they are fine for that application.
Definately agree with the above,no nylon or karbo gears for your plane,or the G38 ones..
The 645's are old school,reliable,tough and affordable.I have heard guys with G 62's running them.You can put them on 6 volt for extra power without any issues.They tend to get some play in them after a bit,but for sport use its not an issue.