Cylinder Block Assembly: Description and Operation

Crankcase:



The crankcase comprises the two crankcase halves as well as the vertically split (along center of crankcase) bearing case. The bearing case is made of aluminium, but 7 bearing shells are made of nodular cast iron (see arrows).

This construction means that changes in the bearing clearance resulting from thermal fluctuations are reduced by a considerable degree which, in turn, reduces mechanical noise. An additional benefit is that, when the engine is warm, the oil flow at the main bearings is not significantly increased by the constant bearing clearance (virtually identical thermal expansion coefficients between steel/crankcase and nodular cast iron/bearing shells).

Cylinder Sleeve:

To reduce the wear along the cylinder sleeves to a minimum, a production method was chosen whereby a highly porous sleeve (25% silicon and 75% air) is cast directly into the crankcase.
When the sleeve is cast, the air escapes and the silicon remains locally along its path (hence the name LOKASIL).

Bearing Case With Oil-Spray Nozzle:

The Boxster's engine has oil-spray nozzle, used for cylinder cooling to reduce the piston temperature. The injection nozzles are inserted in the bearing case (arrow). To ensure that the engine oil pressure is retained at low engine speeds and at high engine oil temperatures, the nozzle has an opening pressure of 1.8 bar.