... 90 days' warranty !! Bottom price from the factory ! Bicycle engine kit , Rear friction kit , 2S or 4S troke ,90 days ... !! Bottom price from the factory ! ENGINE: F139 2-stroke engine or F142 4- stroke engine as opinion Easy installation, Lower Fuel ConsumptionNew ... U brakect bearing, keep engine output smoothly, and larger powerNew 1.25” Roller design, ...