Internal Components

The combustion chamber is a completely new design having a compact, bi-concave 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 240~ combined with high valve lift (9.7 mm) 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. Refer to S.I. 11 06 90 (3060) for complete information.



The self-adjusting hydraulic tappets function with the use of engine oil pressure, internal chambers and orifice control.
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. Please follow instructions.

Occasionally tappet noise may occur following a cold start. Within certain limits this is normal, see S.I. 11 05 90 (3058) for complete information.



The crankshaft is forged steel supported by five main bearings with 8 counterweights. The 3-layer main bearing shells conform to the BMW Tri-Color classification.



The forged steel connecting rods have been developed specifically for M42 use. The connecting rod bearings conform to the double color 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 35 mm and 54 mm respectively. The 1st to 2nd stage transition point is 22~ 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 "selflearned". 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.