Valve Train Features

The most important design feature is the crossflow cylinder head with four valves per cylinder, double overhead camshafts (DOHC) and bucket-type tappets with hydraulic lash adjusters.


Compared with the M20, the intake and exhaust port areas, exposed when the valves are open, have gone up by 40 percent. Mixture flow through the intake valves is 30 percent higher. Cylinder filling is therefore more complete and the charge-exhaust cycle more efficient.

The combustion chambers are ideally shaped for short flame paths and uniform flame propagation. This makes for efficient combustion and a high level of thermal efficiency, and therefore high specific power output with good fuel economy and low exhaust emissions.

The intake and exhaust valves are arranged in a V pattern, and use dual valve springs to ensure rapid, bouncefree closure.

The self-adjusting hydraulic tappets simplify maintenance, eliminating routine valve adjustments. Fluctuations in performance or exhaust emission levels due to valve clearances changing are a thing of the past. Valve train noise and thermal load on the valves are also reduced due to permanent contact between the camshafts and tappets.



The double overhead camshafts are hollow castings (M20: solid castings) and rotate in seven bearing journals. The camshaft housings are separate components which permit removal of the camshaft and self-adjusting hydraulic tappets without cylinder head removal.



In view of the higher loads imposed by the new valve train, the camshafts are driven by single roller chains which are lubricated and cooled by oil spray jets.


The main drive (primary chain) connects the crankshaft to the exhaust camshaft, with a guide rail on the tension run of the chain and a hydraulically dampened tensioning rail.

The secondary chain runs from the exhaust to the intake camshaft and also has a guide rail and a hydraulically dampened tensioning rail.



The cylinder head cover has been reduced in weight. New rubber elements and components limit noise radiation.

The ignition leads for the direct solid-state distribution system with its six individual coils are integrated into the cylinder head cover.

An oil trap is also integrated into the cylinder head cover. A labyrinth formed by cast webs is sealed at the bottom by a sheet-metal cover with molded rubber seal. Return openings in the webs allow the trapped oil to flow back into the cylinder head. The almost oil-free fumes that remain are conducted to the intake manifold for combustion, in order to comply with pollutant emissions legislation.

An oil shield on the intake camshaft reduces the oil splash accumulation in the crankcase breather.



The single-piece plastic intake manifold with its optimized intake pipe lengths and cross-sections provides a torque curve which ensures immediate response and good flexibility in all engine-speed ranges.

With a weight of approx. 3 kg (6.5 lbs.), the plastic air intake system is about 50% lighter than a comparable aluminum system. Its very smooth inside walls make additional treatment unnecessary. The resulting drop in flow resistance ensures optimum operating efficiency.

The air collector is extremely rigid and therefore emits less noise.