The BMW M20B23 is a 2.3 liters (2,316 cc, 141.3 cu·in) straight-six, four-stroke cycle natural aspirated gasoline engine from BMW M20-family. The engine was manufactured from 1978 to 1987.
The BMW M20B23 engine features a cast-iron block and aluminum head with a single overhead camshaft (SOHC) and two valves per cylinder (12 in total). The cylinder bore is 80.0 mm (3.15 in) and the piston stroke is 76.8 mm (2.99 in).
The first version of the M20B23 engine uses the same head “200” and block as the M20B20 but a longer 76.8 mm (3.02 in) stroke crank. This engine used mechanical fuel injection system K-Jetronic, the compression ratio is 9.5:1 and the redline is 6,400 rpm. This engine produced 143 PS (105 KW; 141 HP) at 6,000 rpm of horsepower and 176 Nm (17.95 kg·m; 129.89 ft·lb) at 4,500 rpm of peak torque.
The 1982 version used L-Jetronic, the 731 cylinder head, a compression ratio of 9.8:1. This version produced 139 PS (102 kW; 137 HP) at 5,300 rpm of maximum horsepower and 205 N·m (20.9 kg·m, 151.1 ft·lb) at 4,000 rpm of torque.
In 1984, the fuel injection system, exhaust, and camshaft were upgraded to LE-Jetronic. Redline increased to 6,500 rpm. This engine produced 150 PS (110 kW; 147 HP) at 6,000 rpm of maximum output power and 205 N·m (20.9 kg·m, 151.1 ft·lb) at 4,000 rpm of peak torque.
The breakdown of the engine code is as follows:
- M20 – Engine Family
- B – Gasoline
- 23 – 2.3 Liter Displacement
General information
| Engine Specifications | |
| Engine code | M20B23 |
| Layout | Four stroke, Inline-6 (Straight-6) |
| Fuel type | Gasoline |
| Production | 1977-1987 |
| Displacement | 2.3 L, 2,316 cc (141.3 cu in) |
| Fuel system | Mechanical fuel injection system (Bosch K-Jetronic) Electronic fuel injection system (Bosch L-Jetronic, LE-Jetronic) |
| Power adder | None |
| Max. horsepower | From 139 PS (102 kW; 137 HP) at 5,300 rpm to 150 PS (110 kW; 147 HP) at 6,000 rpm |
| Max. torque | From 176 Nm (17.95 kg·m; 129.89 ft·lb) at 4,500 rpm to 205 N·m (20.9 kg·m, 151.1 ft·lb) at 4,000 rpm |
| Firing order | 1-5-3-6-2-4 |
| Dimensions (L x H x W): | – |
| Weight | 170 kg (374.8 lbs) |
Cylinder block
The BMW M20B23 engine has a cast-iron cylinder block, bore is 80.0 mm (3.15 in) and stroke is 76.8 mm (2.99 in). The cylinder block, a monoblock specially cast structure. The pistons are each fitted with two compression rings and a single oil ring.
| Cylinder block | ||
| Cylinder block alloy | Cast iron | |
| Compression ratio: | 9.5:1, 9.8:1 | |
| Cylinder bore: | 80.0 mm (3.15 in) | |
| Piston stroke: | 76.8 mm (2.99 in) | |
| Number of piston rings (compression / oil): | 2 / 1 | |
| Number of main bearings: | 7 | |
| Cylinder inner diameter (standard): | 80.000 mm (3.1496 in) | |
| Piston skirt diameter (standard): | 79.980 mm (3.1488 in) | Piston ring side clearance: | Top | 0.040-0.080 mm (0.0016-0.0031 in) |
| Second | 0.030-0.070 mm (0.0012-0.0028 in) | |
| Oil | 0.020-0.050 mm (0.0008-0.002 in) | |
| Piston ring end gap: | Top | 0.200-0.500 mm (0.0079-0.0197 in) |
| Second | 0.200-0.500 mm (0.0079-0.0197 in) | |
| Oil | 0.200-0.500 mm (0.0079-0.0197 in) | |
| Crankshaft journal diameter: | 60.000 mm (2.3622 in) | |
| Crankpin diameter: | 45.000 mm (1.7717 in) | |
Main bearing cap bolts tightening procedure and torque specs:
- 60 Nm (6.12 kg·m; 44.28 ft·lb)
After securing bearing cap bolts, make sure crankshaft turns smoothly by hand.
Connecting rod bearing bolts
- Step 1: 5 Nm; 0.51 kg·m; 3.69 ft·lb
- Step 2: 20 Nm; 2.04 kg·m; 14.76 ft·lb
- Step 3: Tighten bolts at the angle of 70°
Cylinder head
The cylinder head is made of an aluminum alloy with good cooling efficiency. The engine has a single overhead camshaft with two valves per cylinder. The camshaft is driven by a timing belt.
Intake valves are 40.0 mm (1.57 in) in diameter and exhaust valves are 34.0 mm (1.34 in). The valves are opened and closed by rocker arms. These rocker arms perform a dual function of cam follower valve adjuster, as one end contains the eccentric and the adjustment nut. The rocker arms pivot around rocker arm shafts.
| Cylinder head | ||
| Valve Arrangement: | SOHC, belt drive | |
| Valves: | 12 (2 valves per cylinder) | |
| Intake/Exhaust duration: | – | |
| Valve head diameter: | INTAKE | 40.0 mm (1.5748 in |
| EXHAUST | 34.0 mm (1.3386 in) | |
| Valve steam diameter: | INTAKE | 7.0 mm (0.2756 in) |
| EXHAUST | 7.0 mm (0.2756 in) | |
Head tightening procedure and torque specs:
- Step 1: 30 Nm (3.06 kg·m; 22.14 ft·lb)
- Step 2: Tighten bolts at the angle of 90°
- Step 3: Once again, tighten bolts at the angle of 90°
Maintenance data
| Valve clearance | |
| Intake valve | 0.25 mm (0.010 in) |
| Exhaust valve | 0.25 mm (0.010 in) |
| Compression pressure | |
| Minimum | 10.2 kg/cm2 (9.9 bar, 145 psi) / 350 rpm |
| Oil system | |
| Recommended engine oil | 5W-30, 5W-40, 10W-30, 10W-40, 10W-50, 15W-40, 15W-50 |
| Oil type API | – |
| Engine oil capacity (Refill capacity) | With filter change 4.25 l Without filter change 4.0 l |
| Oil change interval, km (miles) | 10,000 (6,000) |
| Ignition system | |
| Spark plug | Bosch: W8LCR, NGK: ZGR5A |
| Spark plug gap | 0.7 mm (0.028 in) |
Vehicle applications
| Model | Years Produced |
| BMW 323i (E21) | 1977–1982 |
| BMW 323i (E30) | 1982–1984 |
| BMW 323i (E30) | 1984–1987 |
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