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Lycoming 0-320 series engines

The Lycoming 0-320 series engines of 150-hp to 160-hp look very much like the four-cylinder Lycomings of lesser power. The increased cubic-inch displacement is the result of increased bore. Stroke is the same as the O-235's and O-290's - 3.875 inches. All modern light plane engines of the opposed cylinder layout are over-square. That is, stroke is markedly less than bore. A short stroke holds down piston speeds and reduces wear.

In design and operation, the O-320's tappets are almost identical to the hydraulic tappets used on Continental engines. As the camshaft lobe actuates the cam follower and pushes the hydraulic lifter cylinder outward, the oil in the chamber acts as a cushion. While the engine valve is off its seat a bit of oil leaks between the plunger and cylinder bore to compensate for any contraction or expansion in the valve train. Then, as the cam lobe moves off the follower and the engine valve closes, the supply chamber immediately refills and prepares for another cycle.

The 0--320 series engines have provision in the crankcase (ahead of number one cylinder) for a hydraulic propeller installation. Also, the chrome moly crankshaft on some models are fitted with a pair of small propeller flange bushings which allow this shaft, designed for constant-speed propellers, to accommodate a controllable-pitch prop. But crankshafts intended for constant speed props may not be substituted for shafts in fixed pitch installations unless the plug, in the rear of the hollow front section of the shaft, is installed. (Or removed, if switching from fixed-pitch to controllable pitch). The 0-320 in the used market may or may not have chromed cylinder barrels. Just make sure that you never put chromed piston rings into a chromed cylinder barrel, because something has to give, and chrome against chrome makes this impossible. As a general rule, Lycoming chromes the cylinder barrels of its higher horsepower engines in manufacture, while Continental prefers to use chrome rings.

Internal engine lubrication is conventional on the 0--320s. Mains, con rods, camshaft bearings, tappets, and pushrods are pressure lubricated. Oil collectors and spray lubricate the piston pins, cylinder walls, and gears. The oil pump, located in the accessory housing, sucks oil from the sump and sends it through a drilled passage in the accessory housing a threaded connection on the rear face of the housing, through a flex line and into the external cooler. Pressure oil from the oil cooler returns to another threaded connection on the accessory housing and goes through a drilled passage to the oil pressure screen, which is in a casting mounted on the accessory housing. If cold oil or an obstruction should restrict the oil flow to the cooler, a bypass valve allows the oil to flow directly from the oil pump to the oil pressure screen chamber.

From the pressure screen chamber, oil flows through a drilled passage to the pressure relief valve (located on the upper right side of the crankcase ahead of the accessory housing), and this relief valve maintains proper oil pressure in the engine by diverting excess oil back into the sump. The pressure oil is then fed to the main oil gallery in the right half of the crankcase.

Flowing through this main gallery, the oil is distributed to the drilled passages which take it to the main bearings of the crankshaft. Angular holes are drilled through the mains to the rod journals where sludge removal tubes are located. Thus the centrifugal force of the crankshaft in motion removes sludge and foreign matter that may be in the oil.

Drilled passages from the rear main send oil to the crankshaft idler gear shafts. And oil from the main oil gallery also flows to the cam and valve gear passages, and then through branch passages to the hydraulic tappets and cam bearings. Oil enters the tappet through indexing holes and goes out through the hollow pushrods to the valve mechanism, lubricating the rocker bearings and valve stems.

The 0-320 Lycomings have an ignition system similar to that of the 0-235 arid 0-290 engines, and also employ the Scintilla 84LN-20 and 21 magnetos, except as noted in the model list below. The induction system, too is practically the same, except that the 0-320 is fitted with a Marvel-Schebler MA-4SPA carbureytor.

The AN 20010 propeller governor drive furnished with the 0-320 allows installation of a constant speed governor and a single - acting controllable pitch prop. High pressure oil is carried from the governor, which is mounted on the accessory housing, to the front of the crankcase by way of an external oil line. The oil then flows into the hollow front section of the crankshaft through indexing holes in the crankcase, front main bearing, and crankshaft.

Specifications - 0-320-A

Cylinder bore 5.125 in.
Stroke 3.875 in.
Displacement, cubic inches 319.8
Compression ratio 7.00:1
Rated rpm 2,700
Rated horsepower 150
Cruising rpm 2,450
Dry weight 268 lbs.
Oil pressure, normal 65 to 85 psi
Oil pressure, minimum at idle 25 psi
Oil sump capacity 8 qts
Fuel grade, octane 80/87
Spark advance, BTC 25 degrees
Tappet setting, cold engine .028 to .080 inches


Lycoming 0-320 Series

Following is a complete list of the 0-320 series:

Model

Hp

rpm

Fuel

C.R.

Description

0-320-AlA

150

2700

80/87

7.00:1

Controllable prop, 25-deg spark advance

0-320-A2A

150

2700

80/87

7.00:1

Same as A1A but fixed pitch propeller

0-320-A3A

150

2700

80/87

7.00:1

Same as A1A with 7/16" prop bolts

0-320-A1B

150

2700

80/87

7.00:1

Same as A1A with straight riser in oil sump and -32 carburettor

0-320-A2B

150

2700

80/87

7.00:1

Same as A2A with straight riser in oil sump and -32 carburettor

0-320-A2C

150

2700

80/87

7.00:1

Same as A2B with retard breaker mags

0-320-A2A

150

2700

80/87

7.00:1

Same as E3D with conical mounts

0-320-A3B

150

2700

80/87

7.00:1

Same as A3A except for straight riser in oil sump and -32 carburettor

0-320-A3C

150

2700

80/87

7.00:1

Same as A3B except for retard breaker mags

0-320-B1A

160

2700

100/130 or 91/96

8.50:1

Same as A1A but high compression

0-320-B2A

160

2700

100/130 or 91/96

8.50:1

Same as B1A but fixed pitch propeller

0-320-B3A

160

2700

100/130 or 91/96

8.50:1

Same as B1A except 7/16 prop bolts

0-320-B1B

160

2700

100/130 or 91/96

8.50:1

Same as B1A except straight riser in oil sump and -32 carburettor

0-320-B2B

160

2700

100/130 or 91/96

8.50:1

Same as B2A except straight riser in oil sump and -32 carburettor

0-320-B2C

160

2700

100/130 or 91/96

8.50:1

Same as B2B except retard breaker mags

0-320-B3B

160

2700

100/130 or 91/96

8.50:1

Same as B1A except E 7/16 prop bolts, straight riser in oil sump, and -32 carburettor

0-320-B3C

160

2700

100/130 or 91/96

8.50:1

Same as B3B except retard breaker mags

0-320-C1A through
0-320-C3C

150

2700

80/87

7.00:1

Low compression field service conversions of B1A through B3C

0-320-L1A

160

2700

100/130 or 91/96

8.50:1

Same as B3B but type one dynafocal mounts

0-320-D2A

160

2700

100/130 or 91/96

8.50:1

Same as D1A but with fixed pitch prop and 3/8 attaching bolts

0-320-D1B

160

2700

100/130 or 91/96

8.50:1

Same as D1A but retard breaker mags

0-320-D2B

160

2700

100/130 or 91/96

8.50:1

Same as D2A but retard breaker mags

0-320-D1C

160

2700 2700

100/30 or91/96

8.50:1

Same as D2C but provision for controllable prop

0-320-D2C

160

2700

100/130 or 91/96

8.50:1

Same as D2A except-1200 series mags

0-320-D1F

160

2700

80/87

7.00:1

Same as E1F except high compression pistons

0-320-D2F

160

2700

80/87

7.00:1

Same as E2F except high compression pistons

0-320-ElA

150

2700

80/87

7.00:1

Same as A3B but with type 1 dynafocal mounts

0-320-E2A

150/

140

2700/

2450

80/87

7.00:1

Same as E1A but fixed pitch prop, 3/8 attaching bolts, and alternate rating of 140- hp

0-320-E1B

150

2700

80/87

7.00:1

Same as E1A except retard breaker mags

0-320-E2B

150

2700

80/87

7.00:1

Same as E2A except retard breaker mags

0-320-E1C

150

2700

80/87

7.00:1

Same as E1B

0-320-E2C

150/

140

2700/2450

80/87

7.00:1

Same as E2A but -1200 series mags and alternate rating of 140-hp

0-320-E2D

150


2700

80/87

7.00:1

Similar to E2A but with Slick "throw away" mags and 0-235 front

0-320-E3D

150

2700 2700

80/87

7.00:1

Same as E2D but with3/8 prop flange bolts

0-320-ElF

150

2700 2700

80/87

7.00:1

Same as E1C but with prop governor drive on left-front of crankcase

0-320-E2F

150

2700

80/87

7.00:1

Same as E1F but with fixed pitch prop

0-320-E2G

150

2700

80/87

7.00:1

Same as E2D but with0-320-A sump and take pipes

0-320-E2H

150

2700

80/87

7.00:1

Same as E2D but with S4LN-20 and -21 mags

0-320-E3H

150

2700

80/87

7.00:1

Same as E3D but with S4LN-20 and -21 mags

The IO-320's are equipped with Bendix fuel injection systems and are designated 10-320-AlA through AI0-320-C1B. The I0-320-AlA, -A2A, -E1A, and -E2A are 150-hp and use 80/87 fuel. All others are rated at 160-hp @ 2700 rpm with 8.50:1 compression ratios. Significant models are:

LIO-320-B1A

160

2700

100/130

8.50:1

Similar to 10-320-BlA but with left hand rotation
LIO-320- CIA

160

2700

100/130

8.50:1

Similar to 10-320-C1A but with left hand rotation
L10-320- C1A 160 2700 100/130

8.50:1

Same as B1B but converted for turbocharger; long reach spark plugs, piston cooling oil jets, -21 mags and AN fuel pump drive
AIO-320- A1A 160 2700 100/ 130 or 91/96

8.50:1

Aerobatic engine with Bendix RSA-5ADI fuel injection

The aerobatic version is also available with fixed pitch prop (AIO-320-A2A), impulse coupling magneto (-A1B), and front mounted fuel injector (-B1B).