58-26-01 BELL: Applies to All Models 47G2 and 47J Helicopters With Engine Cooling Fan Index Plate Assembly, P/N 47-661-801-5 Installed.
Compliance required within next 25 hours of operation.
Fabricating procedures used on the engine cooling fan index plate assembly, P/N 47-661-801-5, which involve silver brazing have resulted in a possible defective bond between the fan index plate and the fan shaft. To prevent failure of this joint, all Models 47G2 and 47J helicopters having silver brazed index plate assemblies must be reworked as indicated:
1. Locate the longitudinal center line of portion of the 47-669-117-5 shaft on which the fan mounts and drill one 0.2130-inch diameter hole (blind) 0.63-inch deep through the 47-669-106-5 or -7 index plate and into the end of 47-669-117-5 fan shaft.
2. Locate the intersections of a line between the two end indexing holes and the end of the 47-669-117-5 shaft which projects through the indexing plate and drill 0.2130-inch diameter holes.
3. Tap all three holes using a 1/4-28UNF3A tap and install AN 4H4A bolts and AN 960-416 washers. Safety wire the heads of all three holes with AN 995C32 lockwire.
Model 47G2 helicopters, Serial Numbers 2213, 2214, 2229, 2230, 2231, 2232, 2235 and subsequent, and Model 47J helicopters, Serial Numbers 1420, 1581, 1713, 1731, 1734, 1737, 1743, 1744, 1747, and subsequent will have reworked or heli-arc welded index plate assemblies, identified as P/N 47-661-801-25 or P/N 47-661-801-21, installed prior to delivery and are not affected by this directive. In addition, some early 47G2 and 47J helicopters equipped with fan index plate assemblies marked as P/N 47-661-801-5 are steel welded in a satisfactory manner and need not be reworked. These may be identified by a 1/4-inch deep by 0.56-inch diameter counterbore in the aft end of the engine cooling fan shaft. A flashlight and mirror are needed to determine the existence of the counterbore.
(Bell Mandatory Service Bulletin No. 126SB dated October 2, 1958, covers this same subject.)