3920868 Exhaust Valve For Cummins 4BT/6BT (Pair) 3802356Two New Aftermarket Replacement 3920868 Exhaust Valves for Cummins 4BT 6BT B Series Engines (Pair) This listing includes two (2) new aftermarket replacement exhaust valves for Cummins 4B and 6B B Series diesel engines, including the 4BT 3. 9L and 6BT 5. 9L. The exhaust valve seats in the cylinder head and controls the expulsion of combustion gases from each cylinder, playing a direct role in engine sealing, performance, and emissions. Replaces OEM