Typical engine model is O-320-E2D or AEIO-360-B4A. What do all these numbers mean?

General format is:

Prefix letters- Displacement - Suffix letters - Prefix letters;

 O = Opposed Cylinders

 I = Fuel Injected (if no I, then carb model)

 T = Turbo Supercharged

 A = Aerobatic, typically comes from factory with a Christen Inverted oil system but also may have heavier crank flange

H = Helicopter:

L = Left hand rotation

Displacement, In Cubic Inches. 235, 290, 320, 360.

Suffix letters is in the form:

 Power Section, Nose Section, Accessories

Power Section deals with crankcase type, cylinders, etc.

 Codes used: A, B, C, D, E (see below)

Nose Section defines setup for propeller:

 1 & 3 = Controllable Propeller

 2 = Fixed Pitch Propeller

Accessory Section:

A = Rear Mounted Accessories, Bendix mags

B = Different mag's

D A 'D' on the end (4th or 5th letter of suffex)

indicates the Bendix 'Dual mag' in single housing.

6 On 4 cyl, a 6 indicates one sixth order and one eighth order

counterweights on crank. Only on 200HP as far as I know,

for example IO-360-A1B6D.

? Other letters identify the Mag's, oil sump, carb variations

Serial Numbers

In addition to the engine model number, you have to use the Serial

Number

to obtain additional information.

Serial numbers end with a 'dash number', such as '-27' which

identifies

the engine type:

-27 is for all O320 A and E engines (ie 150 HP).

-39 is for all O-320 B, C and D engines (ie 160 HP)

The 'dash number' may be followed by a letter.

A 'A' designates a 'Wide Deck' engine and the lack of the 'A' means it

is a 'Narrow Deck' engine. This applies to O-320 and O-360 engines.

For example, O-320-A2B engines come in both narrow and wide deck

models

and you must know the serial number to determine what type it is if

you are talking to someone on the phone and can't see the engine

yourself.

Wide Deck engines have a larger diameter bold circle at the cylinder

base

(thus the name) and the cylinders have a thicker base flange of a larger

diameter than the narrow deck cylinders.

The high compression narrow deck engines (160 HP O320's and the 180HP

O360's) have a 'doubler' or hold down plate atop the cylinder base

flange.

This reinforces this area where the cylinder bolts to the case.

Most internal parts are the same on narrow and wide deck engines but

check the parts book for sure when ordering or swapping parts.

O-320's

========

The O-320's come in 150 HP (low compression) and 160 HP (high compression) versions. The other main difference is what motor mount style the crankcase is setup for (conical or dynafocal). Conical mount uses the simple pair of 'cone' rubbers at each mount and the bolts are parallel with the crank. The dynafocal mounts use the larger rubber biskets and the bolts are angled to point to the center of mass of the engine and prop. The fixed pitch are Type 1 mount (30 degree) and the constant speed prop engines use the Type 2 (18 degree) as the heavier prop shifts the mass forward. The dynafocal mount was designed to cancel out a lot of the vibration.

O-320 A 150 HP, conical mount, low compression. E 150 HP, Dynafocal mount, Type 1 (30degree), low compression Some models derated to 140HP and 2450 RPM.

O-320 B 160 HP, conical mount, high compression D 160 HP, Dynafocal mount, high compression

O-320 C 150 HP, field conversion of O-320-B to 150 HP low compression

O-320-H 160 HP. This is a "unique" engine and different from A, B, C, D engines. Most parts DO NOT interchange with the other engines. This is the famous engine used in Cessna 172's between 1979-1981(??). Numerous AD's and Service Bulletin

apply. Not recommended for use on RV 3/4/5 due to motor mount problems on the rear dynafocal ring and the fuel pump is in front and will hit the cowl. 9:1 compression ratio.

Example O-320-H1AD, has integral Acc case, front mounted fuel pump, external oil pump, and D4 RN-2021 dual magneto.

IO-320 A 150 HP, low compression, 7.0:1

A- Type 2 dynafocal mount.

IO-320 B, C, D, F, High Compression 8.5:1 160 HP

B- Type 2 (18 degree) Dynafocal mount

C- Type 2 Dynafocal mount, setup for turbocharging,

piston cooling, long reach plugs, etc.

D- Type 1 (30 degree) Dynafocal mount

F- Same as C but with Type 1 mount.

NOTE: IO-320-B1A not suited for RV 3/4/6 unless

oil sump and induction tubes changed.

O-360's

=======

The O-360's come in both 180 HP and 200 HP models. The 180 HP engines are all 'parallel valve' engines, like the O-235/290/320s and come in both carb and fuel injected models. The 200 HP engines are all fuel injected (IO) and have the 'angle valve' cylinders (supposedly for beather breathing). These engines are wider and heavier and have larger cranks, rods, etc. than the 180 HP versions. This is tricky because the IO-360 by itself is not enough to tell if you have a parallel (180 HP) or angle valve (200HP) engine. You must look at the suffex to be sure.

O-360 A and C are high compression 8.5:1, 180 HP @ 2700 RPM parallel valve.

-A has Dynafocal mount

-C has Conical mount ( serial number -36)

O-360 B and D are low compression 7.2:1 168HP @ 2700 RPM parallel valve.

-B has Dnyafocal mount

-D has Conical mount ( serial number -36)

IO-360 A, C, and D high compression 8.7:1 200 HP @ 2700 RPM Angle Valve with Bendix Fuel Injection.

-A Dynafocal mount type 1(30 degree)

-C Dynafocal mount Type 1(30 degree), rear air inlet for Fuel Injector.

-D Dynafocal mount Type 2(18 degree), (serial number -51)

IO-360 B and E high compression 8.5:1, 180 HP @ 2700 RPM parallel valve

B type 1 30 degree Dynafocal mount

E Type 2, 18 degree Dynafocal mount

AIO-360 is Aerobatic.

AEIO-360 is AIO360 with Aerobatic kit, Serial Dash -63).

Some Dry weights:

O-320-A, E 244 lb 150 HP

O-320-B, D 255 lb 160 HP

O-360-A 265 180 HP

IO-360-A, C 293 200 HP

AEIO-360-A 299 200 HP aerobatic

Another issue is prop bolt diameter. I have not been able to determine any number that indicates the bolt diameter. The O-320's have either 3/8 or 7/16 prop bolts and it varies by engine model. The O-360's have 1/2 inch bolts. The Lycoming article noted at the top of this article indicates the prop bolt diameters.

Another reference is an article by Alfred Scott "For-Cylinder Lycomings" published in "Light Plane Maintenance", Dec. 1989, Vol 11, No 12. I think he wrote this for the Falco builders.

For more info on Lycomings, contact

Lycoming

652 Oliver Street

Williamsport, PA 17701

(717) 323-6181

FAX (717) 327-7100

High or Low compression ration (determines type of Fuel you can burn) Low compression can use auto fuel. Carb or Injector? If injected, determine Injector model. Bendix is the most common but some have the very expensive Simmonds FI. If injector, Injector mounting location (bottom, rear, front).

The End.