OK i an at a loss on my savage 25 my engine will start and all it does is spin my spur gear my spur gear is new and to specs tighten and turn back 1/2 back to loosen i know its not that .so i took my 2 speed trans apart and checked everything and no bad gears nothing wrong with it put it back on and boom same thing spur gear spins when motor is at idle increase idle just spins faster can any one help its got me stumped. please help?

Are you saying when you give it gas the spur spins but the truck doesn't move? If so, check for the grub screw on the driveshaft cup. If you didn't use locktite on it, it's probably gone.

Check your clutch, spur shouldn't spin at idle.

You are missing a pin in the back of the aluminum plate... it is a pin that cross the shaft and engeges with the aluminum plate... If something confused, type in google hpi savage 25, scroll to the result that says HPI Racing - Instructions for savage 25 and go to the page 60 exploded view... you will see the pin Z260 that goes before part 86130 "the aluminum plate"...