4-stroke Question

[Skitspuce]

I'm new to dirt bikes, but rode sport bikes for about 12 years, and I'm curious about something...
Why do 4 stroke MX bikes need top ends/valves every couple of seasons when a CBR600RR can last much longer with a similar redline (15K), compression, etc? It seems (not that I know what I'm talking about) that a MX engine is just 1/4 of a sportbike engine. Am I way off - was I taking crappy care of my street bikes?

 

[elf]

Most 4 strokes especially the 250fs get run at wide open throttle most of the time. Compared to your street bike which spends most of its time in the cruise mode. How long would your 600 last if you were racing every week? Dirt bikes have to work much harder than street bikes.

 

[Y2Z]

from the second they are warmed up, they are pretty much pinned (for people who race, or people who just ride hard), it takes a hell of a beating like this.