A-R43679-AI Valve, Exhaust (Std)One New Aftermarket Replacement Exhaust Valve (Standard) Fits John Deere Tractors, Combines, and Industrial Equipment This standard size aftermarket exhaust valve is a direct replacement Fits John Deere engines in the 4. 270, 6. 404, and 6. 466 engine families. Exhaust valves control the release of combustion gases from the cylinder head and are a critical component during engine overhaul, top end rebuild, or valve replacement service. Six valves are