the plastic bushing on the end of the shifter should just drop back into the piece on the shifter rail unless something is really bent or worn. BTW, 4th gear on a km145 is straight through with no gear engagement, so if it isn't working, there may be bent forks or shift linkage causing the problem. I had a friend whose sons d50 got stuck in 2 gears, so he slamed the shifter so hard, he shattered the main bearings in the case.