Constructional Engine Components This presentation will explore: Cylinder Block Construction Cylinder Block Sleeves Cylinder Head Construction Cylinder Head Components

Cylinder Block Bottom End View The cylinder block is usually made of cast iron for strength or aluminium for light weight (fuel economy) and good heat dissipation. The underside of the cylinder block houses the crankshaft and main bearings. The cylinder bores pass through the block, where the water jacket surrounds them. Underside view There are mountings for the starter motor, alternator, distributor, cam drives and other components.

Cylinder Block Top View Core plugs seal the coolant jacket holes left by the manufacturing process. The deck surface is ground flat for a good contact to mount the cylinder head. A gasket and high tensile bolts complete the seal between the cylinder block and cylinder head. Depending on the construction and use, there are many drilled, tapped and machined areas. An example of such being the hole for the dipstick.

Cylinder Sleeves Cylinder sleeves (or liners) are precision, steel tubular inserts fitted or pressed into the cylinder block, as walls for the pistons to move in. They are usually made of cast iron or steel, and may also be used to repair badly damaged cylinder walls in cast-iron blocks. Dry sleeves are thin and supported by the cylinder block material. They are not in direct contact with the coolant and are generally pressed into the block. Wet sleeve Wet sleeves are directly exposed to the coolant and are thicker to account for the lack of structural support from the block. Dry sleeve

Wet and Dry Sleeves Dry Sleeves Dry sleeves are pressed into cylinder bores in the block. They do not make contact with the coolant, but are supported by the cylinder block walls. Wet Sleeves The coolant is in direct contact with a wet sleeve, improving cooling efficiency. The wet sleeve must therefore be thicker than a dry sleeve to account for the lack of structural support generated by the block as in the case of the dry sleeve. A seal is fitted at the top and bottom of a wet sleeve to prevent coolant leakage into the crankcase.

Block Girdle Line boring is a precision process of machining an accurately aligned series of bores through the block, for the main bearings. If these holes are not aligned properly, the crankshaft will not turn correctly. A block girdle, or main bearing bedplate, is a one-piece (unit main) cap that fits over the whole of the bottom of the block, for added strength. The block girdle replaces individual main bearing caps and is more common on aluminium blocks.

Cylinder Head (2 Valve) Water jacket holes in the cylinder head match those in the cylinder block, providing coolant passageways from the block to the head. There is a combustion chamber for each cylinder, containing the spark plug and the valves. In a 2-valve system, each combustion chamber contains one intake valve and one exhaust valve. The shape of the combustion chamber depends on valve arrangements and intended gas flow within the cylinder. In the example shown, the exhaust valves are slightly smaller than the intake valves.

Cylinder Head (4 Valve) Cylinder head construction varies with engine design, and combustion chamber design will vary from engine to engine. This is dependent on the valve arrangement, performance required and intended efficiency. The cylinder head shown is an aluminium, four-valve with pent roof type combustion chamber. Passages allow water to flow between head and block, and to allow oil to return to the sump. High tensile (Stretch) bolts clamp the head to the engine block.

Cylinder Head Components The cylinder head contains many components. Cotters Retainers Seals Pivots Rocker arms Valve mounts consist of springs, guides, seats, seals, retainers and cotters. Springs In the case of the OHV layout shown, the valves are opened by pivoted rocker arms moved by push-rods from a camshaft mounted in the block. Push rods Bare cylinder head Valves

Integral Valve Guides An integral valve guide is when the cylinder head material is used as a valve guide. Valve stem Coolant passageways The close clearance hole for the valve is machined directly into the cylinder head. This design is less durable than a separate pressed in guide and not commonly seen today on a modern vehicle. Integral guide The integral type of guide is very common on cast iron cylinder heads, because of the low production cost. Integral valve seat

Pressed-in Valve Guides Pressed-in guides are generally made of cast iron or bronze and are precision components having a valve stem clearance of as little as a few thousandths of an inch. This type of guide may use an interference press fit to the head. Valve stem Spring seat Coolant passageways This separate sleeve arrangement is pressed into an oversize hole in the cylinder head. Phosphor bronze guide This technique simplifies valve guide repair and provides a highly durable solution. Seat insert Valve seats may also be pressed-in types, forced into recesses in the head (also called seat inserts).