COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Omnipol Piston Engines AD/OM-P/4 Piston Pin Circlip - Replacement NK and Installation Procedure Applicability: Walter M4-111, M6-111, M332 and M337 engines. Requirement: 1. Piston pin circlips may be used only once, and shall be replaced with a new circlip after each removal from the piston groove, irrespective of the length of the time in service. 2. The dimensional checks of new circlips and procedures for removal, gap positioning and installation of circlips specified in Omnipol SBs Nos. M4-111/29, M6-111/27, M332/55 and M337/50 shall be observed, using a circlip driver similar in principle to driver P/N Z 2-01503-01. Compliance: At each removal of circlip after 30 September 1974.