AD 54-09-01

54-09-01 RANGER: Applies to All 6-440-C Series Engine Models. To be accomplished as indicated. To preclude the failure of carburetor hotspot heater assembly P/N 7683, 7697, 7699 or 7708, due to corrosion from accumulations of exhaust products which in some instances have been found to completely close the inner passages, the following inspection should be accomplished by July 31, 1954, and additionally, as indicated below: 1. Remove the manifold pipes and inspect the hotspot casting for cracks on both the outside surfaces and the inside carburetor air passages, particularly at the bottom. 2. If no cracks are evident, the hotspot may be replaced with the hot air supply blocked off, per Ranger Engine Service Bulletin No. 91. Since no appreciable benefit in icing protection is provided by the use of the hotspot, it will be permissible to operate the engine with the hotspot blocked off. If the hotspot is blocked off, it is suggested that hot lubricating oil be applied to coatthoroughly the internal passage walls formerly used for exhaust gas circulation through the hotspot; this will tend to retard further corrosion. 3. If it is desired to continue to use a heated hotspot, it should be checked initially, and at 400-hour intervals to ascertain that the hot air passages are unobstructed with carbon or other exhaust gas products. This can most easily be accomplished by blocking off one hot air boss with a plate and pouring into the other hot air passage, 120 cc's of oil or gasoline. If this will not all be contained in the hotspot casting, a new hotspot casting should be utilized since no satisfactory method is known whereby all of the deposits can be removed. 4. If the hotspot has been used unheated since the last overhaul, only the initial inspection in 1. need be performed before normal overhaul.