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Engine block

Engine block


All 4-cylinder engines are water-cooled in-line units with 4 valves per cylinder, 2 overhead camshafts and 2 balancer shafts incorporated in the cylinder block. The engines have fuel injection and are of crossflow type, i.e. with the inlet valves on one side and the exhaust valves on the other side of the combustion chambers. The balancer shafts are designed to overcome vibration and the forces generated by the moving parts of the engine and at the same time reduce the level of unwanted engine noise.


Cylinder block

The cylinder block is a special one-piece casting with the cylinder bores drilled directly into the block. Special oilways for the lubricating system are also drilled into the block.

Two tunnels for the balancer shafts are incorporated in the block. The tunnels have press-fitted aluminium bearing shells in which the balancer shafts run. These bearing shells can be replaced without the need for subsequent machining.

Pistons

The pistons are made of light alloy and have grooves for two compression rings and one oil scraper ring.

The upper compression ring is flat and coated with chrome or molybdenum. The lower compression ring has oil-scraper characteristics and is slightly wider than the upper. The oil-scraper ring is in three parts. The pistons in the B235 are slightly lower than in the B205. They are reinforced internally and designed for trapezoid connecting rods.

Connecting rods

The connecting rods are forgings and incorporate bushings for the gudgeon pins. The gudgeon pin bushings and big-end bearing shells are replaceable.

The gudgeon pin has a floating fit in the piston and connecting rod. The axial movement of the pin is limited in the gudgeon pin hole with circlips. The B235 has sturdier connecting rods with trapezoid small ends.


Crankshaft assembly

The crankshaft is a forging and has ground journals, which are surface-treated by induction hardening. This produces a hard surface finish which is highly resistant to wear. There are five main bearings, with the middle one also serving to locate the crankshaft axially. Oilways are drilled in the crankshaft for lubrication. All main bearing shells are replaceable.


Cylinder head

The cylinder head, a light alloy casting, is bolted to the cylinder block. The combustion chambers are hemispherical with 4 valves per cylinder. This design improves the flow of gases in the cylinders, ensuring effective combustion of the fuel-air mixture and so higher efficiency.

Timing cover and end plate

The timing cover incorporates the oil pump. The timing cover and end plate are both sealed to the block by means of Loctite 518.