The valve guide isautomobile engineThe guide device of the valve. The valve guide acts as a guide for the valve and transfers the heat on the valve stem to the cylinder head through the valve guide.
Chinese name
Valve guide
Foreign name
Valve guide
Definition
Guide device of automobile engine valve
Role
Ensure that the valve moves in a reciprocating straight line
The function of the valve guide is tovalveIt can ensure the reciprocating linear movement of the valve, make the valve and the valve seat ring fit correctly, and transmit the heat of the valve stem to the cylinder head.
The operating temperature of the valve guide is also high, about 200 ℃.When the valve stem moves in the guideValve trainSplashed oil is used for lubrication, so it is easy to wear.Therefore, nodular cast iron orPowder metallurgy materialMake individual parts and press them into the valve guide seat hole on the cylinder head with a certain interference to prevent falling off.SomeengineIn order to prevent the valve guide from loosening, snap rings are used to fix and position the guide.
The lower part of the valve guide extends intoExhaust passageIn order to prevent resistance to air flow, the outer circle of the extension end is made into a cone.There is a clearance of 0.05-0.12mm between the valve guide and the valve stem, so that the valve stem can move freely in the guide.[1]
Valve guide structure
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The valve guide plays a supporting and guiding role for the valve that reciprocates in it, ensuring that the valve and the valve seat can fit correctly and play a role in heat conduction.
There are two types of valve guides: integral type and embedded type.The integral valve guide directly processes the valve stem hole in the cylinder head.The inserted valve guide is pressed into a cylindrical tube in the guide hole of the cylinder head with an interference of 0.015-0.065mm.
The cylindrical surface of some valve guides is machined with a ring groove, which is inserted into a snap ring for positioning to limit the depth of the lower end into the air passage and prevent it from loosening.
There is generally 0.05~0.12mm fit clearance between the valve stem and the valve guide.They are lubricated by the oil splashed from the valve transmission parts.
If the clearance between valve stem and valve guide is too small, it is easy to cause valve stem seizure and poor sealing, which will cause valve burning and reduce power, economy and emissions.
If the clearance between valve stem and valve guide is too large, the following abnormal phenomena will be caused:
① The valve seat is not smooth, the sealing property is reduced, and the wear is accelerated, resulting in valve burning, power, economy, emissions, etc.
②Air intake systemAir leakage makes the mixture of gasoline engine lean.
③ Too much oil seeps down into the combustion chamber or air passage through the gap (especially during the intake process), resulting in increased oil consumption, blue smoke, and accelerated the formation of carbon deposits.
④ During the exhaust stroke, the exhaust gas enters the crankcase through the clearance between the exhaust valve rod and the valve guide.
⑤ When the pressure at the exhaust port is lower than the pressure in the crankcase, the oil leaks to the exhaust port through the clearance between the exhaust valve stem and the valve guide.
The reason for blue smoke when starting is often that the gap between exhaust valve guides is too large. When stopping, the engine oil leaks through the gap between exhaust valve guides, enters the combustion chamber, sticks to the exhaust manifold, and is burned when starting.This phenomenon will reduce or disappear with the increase of engine temperature.
The function of the valve oil seal is to prevent excessive oil from seeping into the combustion chamber or the intake and exhaust passages through the clearance between the valve guide and the valve stem.It is a rubber seal ring installed on the upper end of the valve guide.If the valve oil seal is damaged, too much oil will flow down into the combustion chamber or air passage through the gap between the valve and the valve guide, leading to increased oil consumption, accompanied by blue smoke from the exhaust, accelerating the formation of carbon deposits in the valve and combustion chamber.[2]
Replace valve guide
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The replacement method of valve guide includes the replacement of flanged valve guide and the replacement of non flanged valve guide.
Flanged valve guide
When the whole cylinder head is heated to 100~150 ℃ in the thermostat, take it out and support itThe cylinder coverDrive out the valve guide towards the camshaft side with the valve guide disassembly tool;Then coat the new O-ring with lubricating oil and install it on the new valve guide, and then drive the new valve guide from the camshaft side with the valve guide disassembly tool;After the cylinder head is cooled, drop some cutting oil into the inner hole of the valve guide, and trim the valve guide with the valve guide reamer to obtain a proper fit clearance between the valve stem and the valve guide;Finally, use gasoline or kerosene to clean the cylinder head thoroughly before installation.more
Replace the valve guide without flange
Before removing the cylinder valve guide, use theVernier caliperMeasure the height of the exposed part and make records.When the cylinder head is heated to 100-150 ℃ in the thermostat, take out and support the cylinder head, and use the valve guide disassembly tool to drive the valve guide out towards the camshaft side;Then use the valve guide disassembly tool to drive the new valve guide from the camshaft side, and measure the height of the exposed part of the valve guide while driving the new valve guide bit by bit until it meets the specified requirements;After the cylinder head is cooled, drop some cutting oil into the inner hole of the valve guide, and trim the valve guide with the valve guide reamer (J) to obtain a proper fit clearance between the valve stem and the valve guide;Finally, use gasoline or kerosene to clean the cylinder head thoroughly before installation.[3]
work environment
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(1) Working environment of the valve guide: the valve guide is the guide for the reciprocating movement of the valve. The heat received by the valve head is transmitted to the guide through the valve stem and then to the cylinder head for heat dissipation.In addition to bearing the temperature, the valve guide also bears the side pressure transmitted by the valve transmission mechanism to the valve stem and acted on the valve guide through the valve stem.At the same time, there is no lubricating oil between the motion pairs formed by the valve stem and the valve seat, which is dry friction. The friction force is large and the wear is large, making the gap between the motion pairs larger.The excessive fit clearance makes the valve movement lose its guiding role. The valve is skewed during reciprocating movement, which makes the valve seat and valve unsealed, resulting in air leakage, reduced power, increased fuel consumption, poor emissions, and poor heat dissipation.
(2) Technical conditions of valve guide: according to the working conditions of valve guide, the material of valve guide must have good heat dissipation and wear resistance. ①Conduit material: carbon steel with hardness of 40-45HRC is generally selected. ②It is arranged in V shape relative to the cylinder head centerline.This arrangement can enlarge the water chamber in the middle of the cylinder head and strengthen cooling. At the same time, it can make the combustion chamber design more compact, the valve head diameter larger, the exhaust more smooth and the intake more sufficient. ③The interference of the valve guide must be appropriate.If the interference is too small, the conduit will become loose and oil will leak into the combustion chamber;Too much interference will cause the cylinder head to crack when pressing into the guide tube.The interference is generally 0.027~0.045mm. ④Pressing guide tube: A. Heat the cylinder head evenly to 80 ℃~100 ℃, and cool the valve guide tube to - 40 ℃.B. Quickly install the punch and press the guide tube into the guide tube hole on the cylinder head.When the upper end of the guide tube exposes the inner surface of the cylinder head basin groove, the extension must be in accordance with the factory specified value.Do not extend too much, or the valve spring will be affected.When the length of the catheter is fixed, the upper end of the catheter extends too short, which means that the lower end of the catheter may extend into the airway, which will affect the intake and exhaust.C. After the tremie is pressed, the inner hole shall be reamed as required, with the roughness of Ral.6~0.8μm。The roughness should not be high, because there is no lubricating oil between the guide tube and the valve.In order to prevent the oil from leaking into the combustion chamber from the clearance between the guide hole and the valve, install the valve oil seal on the upper end of the guide tube.[4]
