The Lycoming O-340 is no different than either of its O-320 or O-360 brothers. The same goes for the care and maintenance. The difference is in some of the unique parts used. The 340 is a modified 320 with longer cylinder barrels and a crankshaft with a longer stroke to increase displacement and different piston connecting rods. This increases the compression to 8.5:1 and boosted power output to 170 hp (127 kW) over the O-320’s 150 hp. It is paired with a constant speed prop.
- View O-340 Operating Manual
- View 0-320 / O-340 Overhaul Guide
- View Lycoming O-340 Parts Catalog
- Doyn SA12 STC Re-isussed to D’Shannon Aviation as STC SA3-126
- Doyn Aircraft Kit Installation Drawing 1099 rev B (referenced by STC for installation)
Important items of note: Do not keep prop at max rpm (2700) fore more than 2 minutes. Reduce manifold pressure to 25″ and lower prop to 2500RPM after initial climb-out to around 500-600 AGL.
Some of the parts/modifications unique to the O-340 are:
- Larger center and rear crankshaft bearings
- Larger bearing chambers in the crankcase, making it a -30 case.
- A unique crankshaft
- Shortened connecting rods
- Shorter connecting rod bolts (can be cut down from longer bolts)
- Unique air intake pipes, caused by the step down between cylinder and crankcase.
- Longer push-rods and push-rod tubes
- Carburetor limited to prevent full throttle.