I'm looking into getting an off-road bike. It seems that most off-road bikes require rebuilds at very low intervals (between 10-15k km's). What off-road bikes don't require these kind of frequent rebuilds? It seems like the CRF250 (with the CBR engine) is a likely candidate, as are the bigger bikes like the Vstrom, KLR650 and the GS BMW's. Are there any other bikes that have long-life engines? What causes this short engine life? Is it due to the small oil capacity of these engines, or is it like go-carts, where the riders are looking to extract every hp of performance from these engines?