Dropped Valve?

[rooster300ex]

What causes a dropped valve?

[underpowered]

could be many things. a small burr on the stem, lack of lube, a burr on the guide, sometimes for no reason at all. i stuck a valve in my 400 teh other day for no reason. they were brand new kibble white valves and they just stuck. pulled it out, re ground it, and re-installed it and have not had a problem one since.

[250X_project]

Bad keepers, incorrect timing, and inadequate springs will also do it.