* Valve Float: At very high RPMs, the valve spring may not be strong enough to keep the valve closed against the upward force of the incoming exhaust gases. This causes the valve to "float," meaning it's not reliably seated and can collide with the piston crown. This collision bends the valve.
* Pre-ignition or Detonation: If the air-fuel mixture ignites prematurely (pre-ignition) or explodes violently (detonation), the resulting pressure spike can exert extreme force on the piston and push it upward, colliding with the open exhaust valve.
* Foreign Object: Something like a broken piece of piston, a valve spring, or debris entering the cylinder can strike the valve and bend it.
* Incorrect Valve Adjustment: If the valve clearances are improperly adjusted (too tight or too loose), it can lead to abnormal valve operation and potential interference with the piston. Too tight can cause excessive friction and eventual failure, and too loose can lead to delayed closing.
* Worn Valve Guides: Worn valve guides can allow excessive valve movement, making the valve more susceptible to colliding with the piston.
* Broken or Weak Valve Spring(s): A broken or weak valve spring will allow the valve to bounce or stay open too long leading to a collision with the piston.
In short, the common thread is an unexpected and forceful upward movement of the piston while the exhaust valve is open or in the process of closing. This interference results in a bent valve, a serious engine damage event requiring repair.
