baking soda .NaHCO3 soda ash. Na2CO3 limestone, marble CaCO3 dolomite MgCO3 pot ash K2CO3
A lot of things. Broken/misadjusted cam/cam chain drives valve into piston. Cam lift is greater than valve spring squish, collar breaks, drops valve into cylinder. Bad valve lash. Running too hot. Oiling issues, not enough delivered, old oil, wrong type of oil. Piston dome too large, hits valve. Engine run too fast, float valve springs. Worn/improperly installed valve guides and seats.
The most common cause is over rev ving, the springs can't pull the valve up and closed before the piston hits it. Usually breaks the piston too. THEN ALL HELL Breaks loose.
over speed causing the valve to bounce friction - lack of oil or breakdown of oil at speed. cam chain failure or push rod failure wear of the guides - age related. poor adjustment - burning poor manufacture
