section_path: Types of motor units/Reciprocating piston/Lead in the valve timing
section_name: Lead in the valve timing
paragraph_text: Lead in the valve timing
  
  The above effects are further enhanced by providing lead: as was later discovered with the internal combustion engine, it has been found advantageous since the late 1830s to advance the admission phase, giving the valve lead so that admission occurs a little before the end of the exhaust stroke in order to fill the clearance volume comprising the ports and the cylinder ends (not part of the piston-swept volume) before the steam begins to exert effort on the piston.