47-35-01\tSIKORSKY: (Was Mandatory Note 1 of AD-7L-1.) Applies to Model R4-B Helicopter Serial Numbers 43-46500 to 43-46502 and 43-46504 to 43-46539 Inclusive. \n\nCompliance required before November 15, 1947. \n\nTo reduce the possibility of loss of flight control due to failure of the main rotor links from lack of lubrication, the links should be reworked in accordance with the following instructions. This change involves the removal and inspection of main rotor link, P/N VS 36181 and machining of oil grooves. \n\n1.\tStrip paint from the subject links with a paint remover or lacquer thinner, Specification No. AN-TT-T-256 or equivalent. Do not use scraper or wire brush on links, because small cracks may be filled in and covered. \n\n2.\tVisually inspect main rotor links, P/N VS 36181 by one of the following methods for cracks around link pin hole and longitudinally along what was the flash line in original forging. (See Figure 1.) If cracks are present, links should be scrapped.AD 47-35-01 \n\n(a)\tVisual inspection after re-anodizing; or \n\n(b)\tBy caustic etching; or \n\n(c)\tBy an approved fluorescent-black light method. \n\n3.\tMachine oil grooves. (See Figure 1.) \n\n4.\tRemove burrs and clean after machining. \n\n5.\tInspect the two bearings removed from each of the three subject links. \n\n(a)\tIf bearings removed are P/N AT-16, replace with P/N AT-16-OH bearings on assembly. (Bearing AT-16-OH is an AT-16 bearing with an oil hole added to its outer race.) \n\n(b)\tIf bearings removed are P/N AT-16-OH and retainer washers are damaged or show evidence of foreign matter, they are to be replaced. \n\n(Sikorsky Service Bulletin R-4B No. 10 and Army T. O. 01-230HA-15 also cover this same subject.)