How many km before they require a rebuild? 91 baby blade

Hi and welcome to FixYa,

Offhand, I believe it is not a matter of the 40K to as how the bike was used. It could be as low as 20K and if the bike has always been ridden hard and near redline, then it would be a candidate for a rebuild.

Due to size, weight and cost, this model is a popular starter bike. Having said this, most of the users would be either over revving or under revving depending how aggressive their driving habits are. A '91 CBR250RR would develop max torque at about 12K RPM and 45+HP @ 15K RPM, it therefore would normally be operating on above 10K for "enjoyment" of the ride otherwise most riders would feel the engine to be underpowered, lacking the umpphh.

Of course kms used would be an important factor but not more than the engine noise (valves and timing chain). Aside from this, pls check the forks for sign of leaks on the seals, presence of burned oil in the bottom of the airbox and basically how the bike was maintained, not the exterior/cosmetics but the insides. Another indicator would be if the chain has extended that the rear tire has to be set to farthest setting.

The best judge would be your gut feel.

Good luck and Thank you for using FixYa. Happy Holidays.

These motors rev hard and work hard so there are a few things to look for ,have a look at overall condition if it has original fairings and see if any have been resprayed.check to see if it has a service history,if these motors run good clean oil and fesh filter at regular intervals there is no reason they wont go for 60 + klms also check to see if there is smoke on start up this useally a good tell sign and if there is too much mechanical noise like came chains noisy valves,and if it blows smoke while running,only if it is a 2 stroke this should happen ,if it is blowing smoke take the oil filler cap off and see how much this is breathing eg blowing out a lot of air from there as if it is you need new rings and possibly new piston and rebore,and it means in the motor there could be other nasty things ready to bite the hip pocket as these little screamers can be expensive to repair,if you not sure about a bike see if the seller will take it to a dealer and you pay for a check over by there mechanics and they will do a compression check on it as well ,this will cost you a small amount of moneey but also could save you a lot of money and heart ache, cheers hope this helps out