4F5409 Inner Valve Spring Fits Caterpillar Industrial Construction ModelsOne New Aftermarket Replacement Inner Valve Spring Fits Caterpillar (Fits CAT) Industrial and Construction Engines This aftermarket replacement inner valve spring fits the cylinder head valve train on Fits Caterpillar D series industrial, construction, and gas engines. The inner spring works in conjunction with the outer valve spring to keep intake and exhaust valves firmly seated against the valve seat during operation, preventing blow by and