I haven't heard of any other cases of valve recession for the ZS177MM/NC250 engine. I also find it difficult to understand how adjusting the intake valve too loose would cause valve recession. :shrug:

CO2,

Have you been riding in dusty conditions? Did you oil your air filter? Have you examined your carburetor boots for possible damage? I ask these questions because I wonder if dust is entering the cylinder head with the fuel/air mixture. ;)

I'm wondering the same thing, Spud. If the valves were too loose, they would hardly open, compared to the proper setting.

Yes many time, i used it very dusty roads (fish hunt, cross/enduro trying and travels), carburator is ok , in summer period /session periodic clean of carburator and air filter, i cant same think faulty carb and air filter , totaly wrong valve adjust.

İ suspect to my drive style , a mountain rampage, some times i used high performans(supermoto wheels,13 front+crf250l 40 rear sprocket+high rpm=150+kmh, isee max speed my bike 163kmh short time.) and , to activate compression = valve to crush skirt.

11.5:1 compresion ratio. (some times i used comresion, brakes on mountain road.)