During the power or combustion stage of a piston cycle, both valves are necessarily closed, because the expansion of gases is driving the piston down.
Closed
Closed
Closed
They are closed during the power stage.
Both the intake and the exhaust valve are closed.
-intake: exhaust closed, intake open -compression: exhaust closed, intake closed -combustion: exhaust closed, intake closed -exhaust: exhaust open, intake closed
Closed
Intake,compression,combustion,exhaust.
The engine may backfire excessively. You may also smell a strong exhaust odor in the riding position. In worst cases, it can cause the engine to run lean.
Possible exhaust leak
inboard gas engine exhaust
A straight, gear-driven shaft that contains lobes used to operate the intake and exhaust valves of a reciprocating engine. The camshaft is geared to the crankshaft in such a way that valves close and open at the correct time relative to the position of the piston in the cylinders.