Dear Dirt Rider,If the big five can produce street motorcycles that can go 15 to 25 thousand miles between valve adjustments, why can they not produce a modern four stroke dirt bike with the same valve train longevity? Certainly the manufacturers have the technology. Any suggestions?Regards,Malcolm Christie
Malcolm,It shouldn’t be a problem. We’ll just make the bikes as heavy and complex as a street bike, gear it so high it will never hit the rev limiter, ride where there is no dust or mud, and never ride slow enough to get the engine hot. That should do it.Oh, you don’t want to ride your dirt bike like that? Of course not. Off-road and motocross riding is extreme use. We all keep saying we want featherweight bikes, and now we say we want to have them as reliable as a rock at the same time. Not going to happen. With the new 250cc four-strokes making 35 hp, that is 140 hp per liter. That means a five-liter truck engine would be making 700 horsepower. A stock chevy truck hardly ever needs the valves adjusted either, but if you cranked that same engine up to 700 hp and drove it in the dirt, how long would it live?If we were willing to go back to XR performance and weight levels, we could have self-adjusting valves, but I don’t think riders would settle for that now.Karel Kramer
Malcolm,It shouldn’t be a problem. We’ll just make the bikes as heavy and complex as a street bike, gear it so high it will never hit the rev limiter, ride where there is no dust or mud, and never ride slow enough to get the engine hot. That should do it.Oh, you don’t want to ride your dirt bike like that? Of course not. Off-road and motocross riding is extreme use. We all keep saying we want featherweight bikes, and now we say we want to have them as reliable as a rock at the same time. Not going to happen. With the new 250cc four-strokes making 35 hp, that is 140 hp per liter. That means a five-liter truck engine would be making 700 horsepower. A stock chevy truck hardly ever needs the valves adjusted either, but if you cranked that same engine up to 700 hp and drove it in the dirt, how long would it live?If we were willing to go back to XR performance and weight levels, we could have self-adjusting valves, but I don’t think riders would settle for that now.Karel Kramer
