Valve guide seals are elastomeric components installed on valve guides within cylinder heads, preventing oil from entering the combustion chamber via valve stem clearance. These seals create a positive seal between the valve stem and guide, minimizing oil consumption and reducing smoke. Constructed from materials like nitrile rubber, silicone, or Viton, they withstand high temperatures and constant compression. Variations exist in design – including O-ring, lip-type, and umbrella seals – to suit different valve stem geometries and engine applications. Proper installation requires lubrication and precise positioning to ensure effective sealing without hindering valve movement.