HOSE AS 7N3584 - Caterpillar

How to identify cylinder heads with the two sizes of oil drain holes.If a former head is used with the breather on the valve cover at this head location, it is possible that the crankcase pressure could be enough to restrict the flow of oil out of this head. Oil could then accumulate around the valve mechanism. Excessive oil consumption and carbon buildup on the valve heads could result.
If you are installing either an OR2671 or OR2621 Remanufactured Cylinder Head Group, be SURE to determine the size of the oil drain hole in the head if a valve cover breather is used with this head. Some of the core heads used in these Remanufactured Heads do have the smaller drilled drain hole and therefore should not be used with a breather at that head location. One solution may be to move the breather (or breathers if two are used) to another valve cover on a head with the cored drain hole if other parts on the engine at this cylinder location do not interfere with the disposal tube.
If necessary, the OR1362 Remanufactured Cylinder Head Group can be used. All of these Remanufactured Cylinder Heads have a core head with the larger cored oil drain passage and will work with the breather (breathers) at any location(s). When this head is used, be sure to use the 2R6806 Connector in the fuel line and that the injectors have fuel screens. See Reference Article.