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The structural characteristics and assembly technology requirements of diesel engine cylinder head assembly

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Through the introduction of the structural characteristics and assembly technology requirements of diesel engine cylinder head components, to improve people’s understanding of diesel engines, and then improve the quality of diesel engine repair quality.

Diesel engine cylinder head assembly is mainly used to close the cylinder, in addition to many important tasks. Its main parts are the cylinder head, cylinder head cover, cylinder gasket and valve assembly. The structure of the cylinder head assembly differs according to the way the diesel engine is burned and cooled. We should understand the structural characteristics and assembly technology requirements of diesel engine cylinder head components in order to improve the quality of diesel engine repair. The following focus on the role of the main parts of the diesel engine cylinder head assembly, structural characteristics and assembly technology requirements.

1 cylinder head, cylinder head gasket, cylinder head bolts, cylinder headcover

The cylinder head is fastened to the body with cylinder head bolts according to a certain tightening torque, and the piston and cylinder liner constitute the combustion space, in the cylinder head there are generally intake and exhaust channels, cooling water chamber (water-cooled diesel engine), lubricating oil orifice. The cylinder head has finely machined holes and flat surfaces for the installation of valve seats, valve guides, valves, valve springs, injectors, intake and exhaust pipes, etc. The cylinder head is fitted with a cylinder head gasket to compensate for the flatness error between the cylinder body and the cylinder head joint surface to ensure cylinder sealing. The cylinder gasket should meet the requirements of high temperature resistance, corrosion resistance, not easy to break, the ability to compensate for the flatness error of the joint surface, easy to disassemble, reusable and so on. Diesel engines mostly use steel (or copper) plus asbestos cylinder gasket. Covered with steel (or copper) asbestos, the cylinder hole around the steel rolled edge, waterway holes, oil holes around the copper rolled edge. To improve its thermal conductivity and reduce the temperature difference between the cylinder head and the cylinder body, copper shavings or steel wires are mixed with asbestos. The cylinder head cover is used to close the valve rocker room, and some models are equipped with pressure reducing mechanism and oil pressure indicator. The cylinder head is not only subjected to the high temperature and pressure of the gas, but also to the great preload of the cylinder head fastening bolts. The heat load on the cylinder head is very serious, and the temperature distribution on its bottom surface is extremely uneven. The most serious part of the thermal stress is between the intake and exhaust valve seat and the valve seat and combustion chamber between the block, the most vulnerable to thermal fatigue and cracking. Diesel engine economy, power, reliability and cylinder head has a direct relationship.

Cylinder head and other parts installation technical requirements are as follows: (1) cylinder head bottom plane should be flat, there should be no warping, pits, pockmarks and other defects. (2) cylinder head by the machine.

cylinder head

After mechanical processing should be after 0.4MPa water pressure test, lasting more than 2min shall not leak. (3) air-cooled diesel engine with aluminum alloy casting, the periphery of the heat sink, to accelerate cooling, shall not be blocked. Water-cooled diesel engine cylinder head casting with waterway must ensure that the smooth. (4) Valve seat ring, valve guide, combustion chamber inlay and installation hole interference fit, heating the cylinder head or pressed in with special tools when installing. When pressing in the combustion chamber insert, pay attention to the orientation of the main spray hole and do not shift. (5) The intake and exhaust channels and cooling water channels on the cylinder head need to be carefully cleaned and must not have mud, sand, iron filings, abrasive paste and other dirt. (6) The cylinder head gasket has a certain thickness and must not be increased or decreased arbitrarily, nor can it be installed in reverse to avoid blocking the oil channel hole and water channel hole. The quality of aging, warping and uneven or the edge of the package should be replaced. There should be no debris, sand or grease between the cylinder head gasket. (7) cylinder head bolts according to a certain tightening torque diagonal tightening, not too loose, too tight or loose tight.

2 valve, valve seat ring

The valve has into, exhaust valve, with the corresponding valve seat ring, the valve work is to open and close, in the diesel engine intake and exhaust strokes in the cam The valves open and close during the intake and exhaust strokes of the diesel engine under the action of the cams to draw in or discharge the gas. Valve stem wear will make the valve stem and the tube fit clearance increased, easy to cause the valve skew, and because of poor closure and air leakage. Poor valve sealing, in compression and work stroke, the gas in the cylinder will leak out, resulting in a decrease in diesel engine power, increased fuel consumption, starting difficulties, etc. Valve wear can be checked by measurement, if the measured size does not

If the measured size does not meet the requirements, the valve should be replaced.

Valve and valve seat ring installation technology requirements are as follows:

(1) there are cracks, corrosion is serious, as well as burned valve and valve head thickness is too thin can not guarantee the valve seal, generally need to change the new valve. The thickness of the valve cone edge allows heating pier thickness repair, and heat treatment also allows to reduce of the diameter to use

Valve rod and valve guide clearance should be adjusted in accordance with the original machine instructions, generally 0.05 ~ 0.10mm.

(2) In order to ensure that the diesel engine works valve seat ring does not fall off, and the cylinder head combined with good heat dissipation, the valve seat ring and cylinder sleeve with an interference fit. When the use of cold set, with the interference amount of 0.04 ~ 0.12mm; with hot set, with the interference amount of 0.20 ~ 0.25mm, the seat circle of the roundness and cylindricity should not be greater than 0.02mm.

3 Valve guide

Valve guide is to guide the valve for linear movement, to ensure that the valve and the seat coaxial fit. The clearance between the valve stem and the valve guide is very small, and the surface of the valve stem is machined smooth to reduce the sliding friction during movement. If the valve stem and guide fit clearance due to wear are too large, then the oil will enter the combustion chamber from their gap, resulting in the phenomenon of “flicking and burning oil”. The valve guide is not normally disassembled, but when the wear is severe and the valve stem clearance exceeds the permissible limit, it needs to be replaced with new parts.

Installation technical requirements are as follows: (1) valve guide and hole interference fit, installation with special tools pressed into. After installation, the cylinder head should be a certain height above the cylinder head plane. The fitting requirements for each model can be found in the manual of each model. (2) The inner diameter of the guide should be smooth, with a surface roughness of Ra0.4μm. no scoring, eyelets, loosening, dents, cracks and other defects are allowed. The bore and valve stem fit clearance is small and should be replaced when the limit is exceeded. For each model, see the manual of each model for the clearance between the inner hole of the tube and the valve stem. (3) The tube with oil hole, the oil hole up when installed (horizontal diesel engine).

4 valve spring, spring seat, valve lock clip

The valve spring enables the valve to close tightly and automatically. The valve spring is supported by the valve spring seat. The valve spring is connected to the end of the valve by the valve locking clip and the spring seat. The valve locking clamps are two half conical bodies, which are self-locking after assembly due to spring tension, and snap into the sloping groove at the end of the valve stem to prevent the valve from falling off.

Installation technical requirements are as follows:

(1) Each model has certain requirements for the length and elasticity of the valve spring. The elasticity should be checked during maintenance, and the spring should be uniform, smooth and flat, with no cracks, scars, rust, crookedness or other defects allowed.

(2) The locking clip must be installed in such a way as to ensure that it enters the spring seat and snaps onto the end of the valve stem with the two pieces being level. When installing the valve assembly, the locking clip must be installed correctly in order for the spring to be installed securely.

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