Airplane Application:
Cessna 172N Skyhawk
Cessna F172N Skyhawk
Beech Dutchess 76
Engine Application:
Lycoming "76" series engines.
Engine models in this series:
O320H2AD
O-360 E1A6D
LO-360 E1A6D
Summary:
The 76 series engines are of a different design than other Lycoming engines. Because of this they have some unique inspection recommendations. Because there weren't many of these engines built, these inspection recommendations might not be familiar with many mechanics or owners.
The "76" series engines use solid lifters instead of the typical hydraulic lifters used in most other Lycoming and Continental engines. Although it is a good idea to inspect valve-to-rocker arm clearance "dry tappet clearance" on any aircraft engine, it is much more important on solid lifter engines.
On engines with hydraulic lifters, the hydraulic plunger automatically reduces valve clearance to zero over a wide range of dry clearances (8 to 80 thousands). On solid lifter engines (which this article is about) there is no compensation. If valve clearance is not within specifications, then valve pounding and valve leakage results.
If these engines are maintained in accordance with Lycoming's instructions they have a fine history of lasting to engine TBO (2,000 hours) without cylinder removal. Included in these recommendations are the procedures for inspecting dry tappet clearance. Note that adjusting the clearance is different than other engines. The adjustment of the dry tappet clearance is obtained by increasing or decreasing the number of square washers placed under the rocker arm fulcrum. The washer part number is LW-15709.
It is especially important to inspect clearance if it has never been done or whenever you are installing a cylinder (true for any engine).
