Honda CB300R, CBR300R and CRF250L transmission can lock up critical
A small metal retaining ring inside the transmission can slip off the main shaft. Without it, the gears can slide out of position. Two things can go wrong. The bike can drop into gear by itself while you are starting the engine, causing it to lurch unexpectedly. Or the transmission and rear wheel can seize while you are riding. Dealers replace the transmission main shaft at no cost to you.