Is there a way valves can contact the piston without over-reving leading to valve float?

Question

Is there a way valves can contact the piston without over-reving leading to valve float?

Answer 1

If a worn/loose timing belt jumps several teeth the valves will hit the pistons if the car has an interference motor. This can even happen just cranking the motor over.

Valve float is caused by over revving the motor and the valve springs are not strong enough to close the valves after the cam lobes open them. Not every motor will bend valves when over revved.

Answer 2

If your valves hit the piston,  this is called the valve slapping the piston and it will more than likely going to damage the piston.  valves are only supposed to touch the heads.

Answer 3

There are a few things that can cause valves to contact the piston. One could be incorrect cam timing, mismatched cam( Camshaft that is not designed to work with the current head setup), incorrect valve springs, incorrect valve length or size, and also incorrect valve adjustments, and a head gasket that is too thin.

Answer 4

On an interference engine, timing belt failure can cause piston/valve contact.

Answer 5

Not unless it out of cam timing-or-a broken valve spring

I noticed this in another question but if your valves float from an over rev its only a few thousants they will not "Hang"open and cause them to hit the piston

Answer 6

Ask people familiar with the 6 cylinder Kawasaki engine about what happens when the cam chain tensioner fails to keep the camchain tight.  Pistons hit the valves and bend them.  Most often this happen when starting and the engine backfires just enough to cause the cam chain to jump a tooth or so.  A VERY expensive problem to fix.

Actually, pistons CAN hit valves when the engine is over reved.  A couple of years ago I rebuilt a KZ1100 engine that a guy over revved.  The #1 piston hit the exhaust valve, bent the valve stem and twisted the pressed together crankshaft.  Had to replace the valve and crankshaft.  Other times over reving will let the valve slam shut, popping the head of the valve off.  When that piece goes to rattling around inside the cylinder, that ain't good and usually destroys the head and twists the crank or bends the connecting rod.