What do you mean by melting spurs?. If your talking about the spur gear it self getting so hot that it softens & then the pinion gear strips it then may
be your slipper clutch needs to be tighter,A loose slipper clutch could cause the spur to over heat, As your running a power full system.

1) Tighten slipper clutch

2) Try largest spur & smallest pinion gear check temps

3) If temps are good fit the next size up pinion gear until you have good speed & good temps, Adjust gearing to suite I mean.

Castle creations have gearing charts aswell. Hope that helped.