[Jeff in Kentucky]

How long will these engines last? Generally, the smaller the engine, air cooled instead of water cooled, and if it has higher compression for more power, the shorter the life. A 250cc Ninja might last 50,000 to 80,000 miles before a rebuild, depending on the quality of the oil, how often the oil is changed, how it is ridden, how maintenance is done, and pure luck. Here is a short site about some maintenance tips for the older and newer 250 Ninjas, with some links for more reading or question asking:

http://www.theyeagergroup.com/ninja_250_maintenance_log.htm