The cylinder block acts to maintain the compression pressure with the piston and receive the combustion pressure. Recent cylinder block consists of the aluminum cylinder block and the cylinder liner. However, there are engines without cylinder liners (2ZZ-GE engine). Also there are cylinder blocks made of cast iron. The cylinder bore is a cylindrical shape. However it becomes inclined for the upper part of the cylinder, which becomes high temperature and high pressure, and the piston thrust side, which is pressurized with the thrust force of the piston to wear. For this reason, the cylind er can become oval shaped or tapered due to partial wear. Various defective conditions resulting from cylinder wear:
Extreme piston-side knocking
Abnormal engine oil consumption
Compression leakage etc.
Abnormal wear and damage inside the cylinder and damage mainly occur for the following reasons:
Improper maintenance of the engine oil or oil filter
Dust being sucked into the engine
Air-fuel mixture too rich
1. Cylinder bore size
Even when brand new, there may be some difference in cylinder bore size due to unevenness in manufacturing precision. For that reason, there are three standard cylinder bore sizes. The size code of each cylinder is inscribed on the top of a cylinder block. In order to increase the precision of piston clearance, standard pistons that match the cylinder size are used. As the size code increases, bore size increases by about 0.01 mm. For some engines, there are four to five standard sizes. Further, there are engines where there is only one cylinder bore size, in which case they do not have the size code inscribed on the cylinder block.
2. Crankshaft main journal bore size
The crankshaft main journal bore is machine-manufactured along with the cylinder block and bearing cap. Differences in crankshaft main journal bore sizes occur from unevenness in manufacturing precision. For that reason, there are several standard crankshaft main journal bore sizes. This size code in inscribed on the bottom of the cylinder block. Use this code when selecting bearings to improve the crankshaft main journal oil clearance precision in order to prevent abnormal noise and seizing and to maintain good fuel economy. As the size code increases, the bore size increases in micron units. Number of standard size, size coding and location of inscription differ according to the engine models.