# AD 77-20-07: Loose Rocker Arm Retaining Studs and Hydraulic Tappets - Type: Airworthiness directive - Status: Current - Products: Lycoming Engines O-320-H1AD, O-320-H1BD, O-320-H2AD, O-320-H2BD, O-320-H3AD and O-320-H3BD - Effective: August 31, 1978 - Superseded by: Nothing supersedes this AD - Product type: Engine - Amendment: 39-3284 - Registered aircraft: 27,398 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/876C1D4E2FF592808625682B0049C609.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/77-20-07 ## The airworthiness directive 77-20-07 AVCO LYCOMING: Amendment 39-3051 as amended by Amendment 39-3284. Applies to O- 320-H series engines, Serial Number L-101-76 through L-3829-76, L-3831-76, L-3843-76 through L-3859-76, L-3864-76, L-3866-76, L-3871-76, L-3902-76 through L-3907-76 and all O-320-H series engines overhauled (Remanufactured by Lycoming) before March 24, 1978. Compliance required within the next 50 hours in service after the effective date of this AD unless previously accomplished. To prevent hazards in flight associated with loose rocker arm retaining studs and failure of the hydraulic tappets, accomplish the following: a. Remove all rocker box covers, rocker arm, fulcrums, spacer washers and push rods. b. Inspect the fulcrum seating surface in the rocker arm for wear steps in excess of .003 inches. Replace all parts found to have such indications. c. Remove the shroud tube springs, shroud tubes and hydraulic tappets from engine. d. Inspect the camshaft lobes for wear or loss ofmetal. Replace the camshaft found to have such indications. e. Replace P/N LW-15168 hydraulic tappets with P/N LW-16168 or P/N LW-16585 hydraulic tappets. (AVCO Lycoming Service Bulletin No. 424 refers to this subject.) f. On engine Serial Numbers 101-76 through 2182-76, remove all rocker arm retaining studs P/N 31- 16 from cylinder head and install new oversize rocker arm retaining studs in accordance with the instruction in Paragraph 3 of AVCO Lycoming Service Bulletin No. 412, dated July 8, 1977, or FAA approved equivalent. g. Equivalent methods of compliance may be approved by the Chief, Engineering & Manufacturing Branch, Federal Aviation Administration (FAA) Eastern Region. h. Upon submission of substantiating data by an owner or operator through an FAA Maintenance Inspector, The Chief, Engineering & Manufacturing Branch, Federal Aviation Administration (FAA) Eastern region may adjust the compliance time specified in this AD. Amendment 39-3051 was effective October 12, 1977. This amendment 39-3284 is effective August 31, 1978. ## Affected data sheets (1) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS E-274](https://openairdocs.org/tcds/E-274): Lycoming Engines; names 6 of 60 models: O-320-H3BD, O-320-H2BD, O-320-H2AD, O-320-H3AD, O-320-H1BD, O-320-H1AD ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 27,398 (0 by airframe model, 27,398 by engine model) - Makers: Piper 11,632, Cessna 9,982, Grumman American Avn. 605, Bellanca 588, Beech 398, Champion 295, Robinson Helicopter 289, American Champion 250, American 116, Gulfstream American 95 Models with the most aircraft: - [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series): 27,057 aircraft (engine model) - [Lycoming O-320 series](https://openairdocs.org/engine/lycoming-o-320-series): 256 aircraft (engine model) - [Lycoming O-320-H2AD](https://openairdocs.org/engine/lycoming-o-320-h2ad): 83 aircraft (engine model) - [Aerotec O-320 series](https://openairdocs.org/engine/aerotec-o-320-series): 2 aircraft (engine model) All 4 models: https://openairdocs.org/ad/77-20-07/models.md Every aircraft: https://openairdocs.org/ad/77-20-07/aircraft.md Its text cites no advisory circulars or STCs. ## NTSB investigations that cite this AD (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB CEN14FA435](https://openairdocs.org/ntsb/CEN14FA435), Aug 17, 2014: Cessna 172N (N734YW), Natchitoches, LA, substantial damage, 1 fatal. Probable cause: The partial loss of engine power due to the exhaust valve rocker retaining stud backing out of the cylinder head, which resulted in the exhaust valve being stuck in the closed position. Contributing… --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.