Cylinder Block

Cylinder Block Introduction

Generally speaking, the cylinder block, the cylinder head, the cylinder head cover, and the oil pan form the engine’s exterior shape. The first of these — the cylinder block — is the largest single component in the engine and is essentially a metal block which has been machined to create both cylinders and a network of oil and water passages for the purpose of lubrication and cooling respectively. In addition, the sides of the cylinder block are fitted with oil filters, with the water pump, and with other similar auxiliary components.

Cylinder Block Section Names

The internal diameter of a cylinder is referred to as either cylinder bore or simply bore. The engine’s displacement is determined by the bore, by the piston stroke (i.e., the distance that the piston travels between TDC and BDC), and by the number of cylinders employed.

The bore to bore interval is known as the bore pitch — that is, bore pitch indicates the distance between the centers of adjacent bores.

The distance from the cylinder top surface to the crankshaft’s center line is called the block height. (This is also true in the case of V-type engines.)

Each cylinder is marked with a different number: in the case of in-line, 4-cylinder engines, the cylinder marked No. 1 is the furthest from the transmission and the other numbers are assigned sequentially in accordance with reducing distance from the transmission.

In the case of a V-6 engine, the furthest cylinder from the transmission is designated as cylinder No. 1 and the other two cylinders in the same bank are designated as No. 2 and No. 3 in accordance with reducing distance from the transmission. The cylinders in the other bank are numbered from No. 4 to No. 6 in accordance with increasing distance from the timing belt.

Cylinder Block Construction

The principal purpose of the cylinder block is to form a housing for the powertrain components — that is, the pistons and the crankshaft. Aluminum has been adopted as the material for the cylinder blocks of engines due to the weight reductions which it allows. The most important section of each cylinder block is its cylinders, within which the engine’s pistons move up and down in a reciprocating motion. Accordingly, sleeves manufactured of a hard material are cast into these cylinders in order that corrosion resistance may be increased. These sleeves will be dealt with in the following section.

Large amounts of heat are generated in combustion, and in order that this heat may be removed from the cylinders, a passage for engine coolant which is known as the water jacket passes around the outside of each. Similarly, the cylinder block is also fitted with passages which allow the supply of lubricating oil to the cylinder head.

Engine Oil Passage

The crankshaft is connected to the underside of the cylinder block via plain bearings, and the lower part of the cylinder block forms the upper part of the crankcase. Furthermore, a section of the cylinder block is often used to form the oil pump case.

Cylinder Sleeves

A cylinder sleeve (also known as a “cylinder liner”) is inserted into each cylinder bore. Since the cylinders’ inner surfaces must resist wear when subjected to the sliding motion of the pistons, these sleeves are made of a hard material.

The inside of each cylinder sleeve is given a fine crosshatch pattern through a machining process known as “honing.” This pattern ensures proper lubrication by maintaining an oil film on the sleeve’s inner surface.

Cylinder sleeves can be classified according to their manufacturing material, whether this be cast iron or fiber-reinforced metal (FRM). Cast iron sleeves offer superior cooling efficiency and rigidity, whereas FRM sleeves are superior in terms of cooling efficiency and weight.

Sleeves can also be classified into single-cylinder and multi-cylinder types. A multi-cylinder type sleeve actually consists of several sleeves joined together. Because this type allows shorter distances between cylinders, its use also permits smaller cylinder blocks to be manufactured. The merit of the single-cylinder type, on the other hand, is its higher cooling efficiency.

Regardless of the fact that hard materials are used, sleeves will wear over extended periods of time. And because the degree of wear that results is not uniform at all points on the sleeves, measurements must be taken at multiple locations when performing wear inspections.

Types of Cylinder Blocks

The following principle classification methods are implemented with respect to cylinder blocks:

Short Skirt or Deep Skirt
Dry Sleeve or Wet Sleeve
Open Deck or Closed Deck

Short Skirt and Deep Skirt Classifications

The term “skirt depth” refers to the distance from the crankshaft center to the bottom of the cylinder block. Accordingly, those cylinder blocks for which this distance is relatively small are classified as short-skirt cylinder blocks; those for which the skirt is long and forms a complete cover for the crankshaft are classified as deep-skirt cylinder blocks.

Dry Sleeve and Wet Sleeve

As mentioned earlier, cylinder blocks are fitted with a number of sleeves. Cylinder blocks for which there is no cylinder wall between the sleeves and the water jackets — i.e., the sleeves are in direct contact with the coolant — are classified as wet-sleeve cylinder blocks. Conversely, dry-sleeve cylinder blocks feature sleeves which do not come into direct contact with the coolant due to the presence of the cylinder wall. It is important to remember that all Honda engines use dry-sleeve cylinder blocks.

Open Deck and Closed Deck

It can be determined whether cylinder blocks are classified as open deck or closed deck by simply removing the cylinder head. If the water jacket (i.e., the coolant passage surrounding the cylinders) is open at the cylinder-head mating surface, then the cylinder block is of the opendeck classification.

Other cylinder blocks — those of the closed-deck classification — feature water jackets which cover the cylinders right up to the top. In this respect, an open-deck cylinder block offers superior cooling efficiency and lower weight.

A closed-deck construction makes the cylinder block more rigid in the vicinity of the cylinder head mating surface, and for this reason, is generally put to use in high-performance engines.