1W5283 Insert-Valve Exh Fits Caterpillar ModelsOne New Aftermarket Replacement Exhaust Valve Seat Insert for Caterpillar (Cat) 3400 Series Engines and Equipment This exhaust valve seat insert (valve seat insert, exhaust) fits into the cylinder head and provides the precision sealing surface where the exhaust valve seats after each combustion cycle. A worn or damaged exhaust valve seat insert causes compression loss, poor combustion efficiency, and accelerated valve wear making this a critical