Cylinder Block Assembly: Description and Operation

Engine Block





All 4-cylinder engines are water-cooled in-line units with 4 valves per cylinder, 2 overhead camshafts and 2 balance shafts incorporated in the cylinder block. The engines have fuel injection and are of cross flow type, i.e. with the inlet valves on one side and the exhaust valves on the other side of the combustion chambers. The balance 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 oil ways for the lubricating system are also drilled into the block.
Two tunnels for the balance shafts are incorporated in the block. The tunnels have press-fitted aluminum bearing shells in which the balance 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 forging 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 circles. 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. Oil ways 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.