AD 77-20-07
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | Lycoming Engines | O-320-H1AD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H1BD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H2AD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H2BD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H3AD | AVCO LYCOMING Model O-320-H Series Engines |
| engine | Lycoming Engines | O-320-H3BD | AVCO LYCOMING Model O-320-H Series Engines |
Unsafe Condition
Loose rocker arm retaining studs and failure of the hydraulic tappets could cause hazards in flight.
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Required Actions
Remove rocker box covers, rocker arms, fulcrums, spacer washers, and push rods. Inspect fulcrum seating surfaces for wear steps exceeding 0.003 inches and replace affected parts. Remove shroud tube springs, shroud tubes, and hydraulic tappets. Inspect camshaft lobes for wear or metal loss and replace as needed. Replace P/N LW-15168 hydraulic tappets with P/N LW-16168 or LW-16585. Install new oversize rocker arm retaining studs for engines serial 101-76 through 2182-76 per Service Bulletin 412. Equivalent methods may be approved.
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Compliance Time
within the next 50 hours in service after the effective date of this AD unless previously accomplished
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Affected Aircraft
AVCO Lycoming Model O-320-H series engines, serial numbers 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 engines overhauled by Lycoming before March 24, 1978.
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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