Engine - 16-Valve S14 Description: Overview
87BMW03GROUP 11 Engine
Bulletin Number 11 02 86 (2052) Page 1 of 8
Montvale, NJ May 1987 Technical Dept.
SUBJECT: Four-cylinder, 16-valve engine (S14)
A high performance 4-cylinder 16-valve engine has been developed by Motorsport GmbH for the 3-Series M3-model. Its concept is based on the S38 six-cylinder 24-valve engine. With a displacement of 2.3 liters and a catalytic converter, the S14 engine develops 192 hp (SAE net) at 6750 rpm.
Although this engine was primarily designed for high performance, additional design objectives were incorporated to make it suitable for every day use. These objectives are low noise level, good response at part load, smoothness over a wide engine speed range and ease of maintenance.
The high power output is achieved mainly by use of a two-deck, crossflow aluminum cylinder head with 4 valves per cylinder (2 intake/2 exhaust valves) and twin overhead camshafts, running in five bearings each. The camshaft bearings are split, allowing the camshafts to be removed upward.
The 4 valves are arranged in a V-configuration, with the exhaust valves operated by one camshaft and the intake valves by the other. Four valves per cylinder increase volumetric efficiency and allow quicker gas flow through the engine. As the weight of the individual valves is lower compared to the usual 2-valve engine, they can be opened and closed more rapidly by using steeper flanks on the camshaft lobes.
The valves are operated directly by the camshafts and bucket-type tappets (2). Valve clearance is adjusted by shims (1) located in the bucket tappet (2) without removing the camshafts. Double valve springs ensure positive valve opening and closing at high engine speeds.
Piston weight has been reduced to enhance mechanical efficiency and minimize friction. The piston pin was moved closer to the piston head by using a longer connecting rod. To prevent any possibility of the valves hitting the piston, four pockets are provided in the piston head.
A double roller chain is used to drive the camshafts. A hydraulic chain tensioner maintains constant tension and a low noise level in all speed ranges.
The combustion chambers are in the cylinder head and include a squish area. This ensures good turbulences of the air/fuel mixture around the centrally located spark plug. This configuration with its short flame path allows a compression ratio of 10.5:1.
The design and dimensions of the cylinder block resemble those of the M 10 four-cylinder engine, but the cylinder barrels are siamesed (cast together) to permit the bore to be increased to 93.4 mm.
The new forged crankshaft with eight balance weights has a stroke of 84 mm. The connecting rods are 144 mm long between the bigand smallend bearing centers.
The engine is carried on two hydro-mountings, which provide improved insulation not only against radiated noise from the engine block but also against vibration.
Oil is supplied to the engine by the standard M10 pump. There is an oil cooler to lower the temperature of the oil. The oil circuit is thermostatically controlled at a new oil filter head (opening temperature 90~C/194~F). The oil temperature is displayed in the lower section of the tachometer. The temperature sensor is on the oil filter head.
The oil temperature shown on the instrument panel is between 80~ and 120~C (176~ and 248~F) with the engine at its normal operating temperature. If the car is driven hard, a maximum value of 130~C (266~F) should not be exceeded.
The oil pan contains an additional oil deflector (windage tray); it diverts oil with a rotary motion from the crankshaft area into the sump, to improve overall mechanical efficiency.
An oil separator, which is mounted to the crankcase underneath the starter motor, separates the oil from the crankcase ventilation vapors, before they enter the intake manifold. The vapors go from the valve cover to the separator; from "dry" vapors are drawn into the intake manifold. The condensed oil flows from the separator back into the oil pan.
To ensure smooth running and compensate for or attenuate vibration, the crankshaft also has a vibration damper. A stiffening shell is installed between the engine block and the transmission housing to reduce vibration.
The cooling system has been increased in efficiency in order to dissipate the heat generated by this engine. The new vertical flow radiator and an electric fan ensure optimum heat exchange. The cut-in temperatures are 82~C/180~F (stage 1) and 91~C/196~F (stage 2). A new water pump housing with a suitable impeller ensures a higher water flow rate. The coolant hoses and thermostat housing have also been modified to accept the greater flow.
For reasons of weight and noise and to prevent corrosion, the intake air cleaner has a plastic body.
To ensure adequate torque and a sufficiently high starting speed even at low outside temperatures, a 1.4 kW starter motor with a planetary gearset is installed.
Fuel injection and ignition of the S 14 engine are regulated by the well-known "Motronic" without adaptive control. An engine speed and a reference sensor are mounted on the flywheel side of the engine. The system features electronic idle control, cold start control and warmup enrichment. The 30 kV distributor is mounted to the exhaust valve camshaft. Fuel system pressure is 3.0 bar. An atmospheric pressure sensor provides compliance with emission standards at different altitudes.
The engine wiring harness is new, to suit the actual operating conditions. The connection plug and the diagnosis plug are of the push-in and screw-on type to ensure good electrical contact. The airflow meter is of revised pattern on account of the increased airflow volume and more marked differences between the minimum and maximum flow volumes. The characteristic curve is logarithmic, to ensure a more accurate signal at low airflows and as a result greater precision in fuel metering.
The fuel tank is vented through an activated carbon filter with extraction at idle speed, to prevent fuel vapor from reaching the atmosphere and contributing to total pollutant emissions.
Intake and exhaust systems had to be completely redesigned to achieve optimum gas flow without unnecessary flow restrictions.
Four separate intake funnels connect the one piece intake manifold to the four separate intake pipes. Each intake pipe has its own throttle plate. The throttle plates are operated synchronously in two groups via two linkage shafts connected to a central shaft running on needle bearings. The synchronized operation of the throttles guarantees excellent emission control and fast engine response.
As part of the PDI as well as with every engine washing, the bearings and the balls and sockets of the entire throttle linkage have to be lubricated with Molykote Long Term Grease, BMW P/N 81 22 9 407 007.
The exhaust gas leaves the engine through a fan-shaped manifold with individual pipes of carefully determined length. The pipes from each pair of cylinders are siamesed, so that two exhaust streams enter the expansion chamber of the muffler system. A crossover connection between the two pipes locates the oxygen sensor. It also provides a a tuned exhaust effect which scavenges the burned gases from the combustion chambers more efficiently.
The idle mixture does not have to be checked/adjusted during inspections. However, checking and/or adjusting the idle mixture is still required for troubleshooting or repairs. The basic adjustment procedure is described below. For specific and current values/details always refer to the current Nominal Value and Repair Manual microfiches! For the idle mixture adjustment, the engine must be at operating temperature (oil temperature greater than 60~C), and the air pressure sensor connected.