BMW has developed a completely new 16 valve, four cylinder engine which is ideally suited for the E30 vehicle. The new M42 engine will be found in two new 3-Series models designated the 318i and 318is.
This engine follows the tradition of other BMW multi-valve engines in that it provides high performance characteristics with excellent routine driveability.
The principle features of the new engine concept are a very flexible power band and excellent torque in relation to the engine displacement of 1.8 litres. Despite the high compression ratio of 10:1 and a power output of 134 bhp, the M42 is a refined, easy-to-drive unit which is especially compatible with everyday use.
Satisfactory acoustic levels are maintained with the use of new technologies and sound insulation techniques.
Low speed vibrations are eliminated with the use of a dual mass flywheel.
Optimum thermal efficiency enables the M42 to provide high power output with minimal exhaust emissions and excellent overall economy.
The new M42 engine exhibits the typical neat appearance and pipe and cable layouts which are found on all present day BMW engines. M42 maintenance requirements are reduced and access to existing service points (spark plugs, oil service) has been simplified.
Cylinder head porting and the inlet and exhaust pipes are designed with adequately large cross sections to provide optimum volumetric efficiency.
The precise cross section and length of the intake manifold-runners ensure effective cylinder filling.
Combustion chamber type and design with the centrally located spark plug result in much shorter flame paths and a more uniform combustion process.
The heart of the new M42 engine is a new crankcase manufactured of pearlitic gray cast iron.
The new crankcase features siamesed cylinder bores and integral oil spray jets for piston cooling. The engine is installed with a 30 degree inclination to the right.
The predominant feature of the M42 engine is the chilled cast aluminum cylinder head, which uses the crossflow principle. The intake and exhaust ports are computer designed and are machined with special cutters for optimum gas flow.
The combustion chamber is a completely new design having a compact, biconcave shape with a centrally located spark plug. The squish zone is distributed between the inlet and exhaust ends of the combustion chamber for minimal energy losses.
The surface of the combustion chamber is cast without machining. This results in a smooth surface which resists the formation of combustion residues.
The combustion chamber volume is divided for effective heat dissipation. The cylinder head accommodates 80% and the piston crown bowl 20%. The large inlet and exhaust ports coupled with dual inlet and exhaust valves ensure that the incoming air/fuel charge is well blended and the exhaust gases evacuated without restriction.
The camshaft housings locate the camshafts and the (self-adjusting) hydraulic tappets. The housings are separate parts which permit removal of the camshafts and tappets without cylinder head removal.
The camshafts rotate in five bearing journals and are lubricated from internal cylinder head oil passages. The relatively short opening duration of 2400 combined with high valve lift (9.7mm) ensure good torque characteristics. The camshafts are of a hollow cast design for weight reduction.
The intake and exhaust valves are arranged in a V pattern with an "included angle" of 39° 45'. The use of dual valve springs ensure rapid, bounce-free closure. Self-adjusting hydraulic tappets reduce valve train noise and lower maintenance costs.
The use of sodium-filled exhaust valves provide effective heat dissipation resulting in long valve life. Due to the unique nature of sodium-filled valves, specific disposal guidelines must be followed when handling or replacing M42 exhaust valves.
The self-adjusting hydraulic tappets function with the use of engine oil pressure, internal chambers and orifice control.
1. Engine oil pressure
2. Large oil chamber
3. Small oil chamber
4. High pressure chamber
Replacement hydraulic tappets are supplied with full oil supply chambers; therefore, proper functioning after installation is assured. Specific procedures must be followed concerning hydraulic tappet spare parts storage, or oil leakage will occur.
Occasionally tappet noise may occur following a cold start. Within certain limits this is normal.
The crankshaft is forged steel supported by five main bearings with 8 counterweights. The 3-layer main bearing shells conform to the BMW Tri-Colour classification.
The forged steel connecting rods have been developed specifically for M42 use. The connecting rod bearings conform to the double colour classification.
New compact, lightweight pistons combined with special length connecting rods reduce oscillating mass and promote smooth running. The piston crowns incorporate a symmetrical combustion bowl and are notched for valve head clearance. The pistons are cooled from oil spray jets mounted in the main bearing oil supply.
A two-stage throttle assembly is bolted to the cast one-piece intake plenum/runner assembly. The 1st and 2nd stage throttle diameters are 35mm and 54mm respectively. The 1st to 2nd stage transition point is 220 of throttle opening travel and provides smooth yet sportslike throttle response.
A throttle potentiometer is used to signal exact throttle position for the DME M1.7 system. Since the engine management system is adaptive, the closed throttle position is always "self-learned". Thus, the throttle potentiometer requires no adjustment and is maintenance-free.
The stainless steel, multiple pipe exhaust manifold is designed for low back pressure restriction and optimum gas flow. Effective heat retention enables the O2 sensor and the catalyst to reach and maintain operating temperatures rapidly.
The M42 is equipped with the latest digital motor electronics engine management system. Designated DME M1.7, the new system features optimized component technology, weight saving design and expanded adaptive self-learning functions.
Functional Diagram of DME M1.7 for M42
1. Fuel tank with pump
2. Liquid/vapor separator
3. Fuel filter
4. M1.7 control unit
5. Ignition coils
6. Spark plugs
8. Fuel rail
9. Fuel pressure regulator
10. Coolant temperature sensor
11. Throttle valve potentiometer
12. Idle control valve
13. Active carbon canister
14. Evap. purge valve
15. Airflow meter
16. Air temperature sensor
17. TDC and RPM sensor
18. O2 sensor
19. Cylinder identification sensor
21. Ignition switch
22. Main relay
23. Fuel pump relay
The M1.7 DME system controls a new multi-coil, "motionless" ignition system. Each cylinder has a separate ignition coil which is controlled by individual DME control unit final stages. The ignition coils are of a new design using a new ground connection and are rated to 30KV.
1. Ignition coil
2. Secondary resistance
3. Spark plug
4. DME final stage
5. New ground path
A new spark plug developed by BMW is used to complete the new M1.7 engine management system. The new spark plug features a 14mm thread, a three-arm "platform" electrode and requires no adjustment. The platform electrode provides a large conductive area which maintains a constant air gap and a uniform flame front during the spark plug's service life.
The new "motionless" BMW ignition system operates without moving parts thus secondary contact wear and tear is eliminated. Other advantages include a wider ignition timing adjustment range, elimination of secondary arcing and stray RFI with improved ignition coil performance during peak loads.
The crankshaft torsional vibration damper and the pulse wheel are combined. As with previous DME systems, the increment teeth signal engine RPM while the tooth gap represents the TDC reference point.
The M1.7 air flow meter is the baffle (door) type and is matched to the engine's specific requirements. As on previous BMW engines, the AFM unit contains an inlet air temperature sensor, requires no adjustment and is maintenance free.
The fuel injectors, fuel rail, cable rail and fuel pressure regulator are mounted to the intermediate intake runner section. This section is adjacent to the intake ports near the intake valves for effective air/fuel mixing.
The cooling system is designed to promote thermal efficiency. Coolant flows vertically up and thru the engine block, thru the cylinder head to the compact vertical-flow radiator.
The 2-stage throttle assembly is coolant heated (de-iced) by a contact type heating element held in place by a bracket. This innovative approach allows a functional check without opening the M42 cooling system.
The M42 cooling system operates with a higher flow capacity than previous BMW 4 cylinder engines due to the new type high output coolant water pump. The temperature regulating thermostat is now rated at 88°C.
The engine oil pan is made up of two cast aluminum sections. The primary section incorporates strengthening ribs at strategic attachment points. As with other BMW engines, this feature creates a "unitized" engine/transmission assembly which reduces flex, vibration and noise.
The cylinder head cover provides ease of service and effective noise reduction. All cylinder head contact points are rubber insulated. A "Stop" incorporated into the holddown bolt shank base prevents insulator grommet distortion from overtightening.
A spark plug cable removal tool is stored in the spark plug recess within the cylinder head cover.
1 Sound Barrier
2 Liquid/Vapor Seperator
Further, an insulation baffle and the crankcase gas liquid/vapor separator act as a barrier for valve train operating noises.
The identical twin camshaft sprockets are driven in clockwise rotation by a duplex roller chain. The chain guides are acoustically insulated to lessen chain drive operating noises.
A newly designed chain tensioner is used which reduces running friction while maintaining correct chain tension. The chain is lubed and cooled by a dedicated oil spray jet mounted in the timing chain housing.
The internal gear engine oil pump is now directly driven from the crankshaft without a chain.
1. Upper chain guide
2. Cam sprockets
3. Primary guide
4. Chain housing
5. Lower guide
6. Idler gear
7. Oil spray jet
8. Tensioner guide
9. Chain tensioner
10. Cylinder I.D. lug
Front view with belt drives
Partial cutaway view of engine
Engine designation: 18 4 SI
Design: 4 cylinder inline (DOHC)
Stroke: 81 mm
Bore: 84 mm
Power: 134 HP/100 kW
At engine speed: 6000 RPM
Maximum torque: 172 Nm
At engine speed: 4600 RPM
Maximum permitted engine speed: 6500 ± 40 RPM
Continuous engine speed limit: 6300 RPM
Compression ratio: 10:1
Inlet valve diameter: 33 mm
Exhaust valve diameter: 30.5 mm
Oil pressure: 4 bar
Oil capacity: 4.5 (filter 0.36) litres
Thermostat: 88 °C
Digital Motor Electronics: M 1.7 ignition system
Firing order: 1-3-4-2
Spark plug (three-arm ground): 0.9 mm electrode gap
CO value: 0.7 0.5%
Idle speed: 850 40 RPM
Premium unleaded gasoline: 90 AKI/95 octane (RM)