to process the guarantee.
in the case of buying the second-hand yow, you must go to the first buyer and ask for information about the purchase (ticket). in the event that there is no ticket that proves the purchase of the yow, the guarantee can not be carried out.
check your yow before every use, particularly the nuts, axles, screws, wheels and bearings which must be correctly tightened.
check if your wheels are properly secured.
check the parts, the screws and nuts should neither too tight or to loose, as both these situations could lead to injury.
if you have to remove the bearings do so with care and always replace them in the correct 