JPH1077812A - Regulation method for valve clearance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve precision of regulation of the valve clearance of an engine, to simplify a regulation work, and to improve work efficiency. SOLUTION: The release end part of the exhaust port 4 of a cylinder head 1 is sealed by a closing member 21. Pressure air is fed from a pressure air feed system 24, and air pressure change characteristics between an opening amount and an air pressure are predetermined by changing an opening amount of an exhaust valve 2 in a state that a given pressure air is fed to the exhaust port 4. When a valve clearance is regulated, the closing member 21 is closed, pressure air of a given pressure is fed to the exhaust port 4, and a gap gage 26 being thicker by a given thickness (d) than a set valve clearance VC is inserted between a cam 11 and a swing arm 12. A regulation screw 13 is regulated until an air pressure in the exhaust port 4 is lowered to a set pressure corresponding to an opening amount equivalent to a given thickness (d) in air pressure change characteristics, and a lock nut 14 is then fastened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a valve clearance of an intake / exhaust system valve of an engine, and more particularly to a method for easily and precisely adjusting a valve clearance via a pressurized gas sealed in a port. About technology.

[0002]

2. Description of the Related Art In a valve train of an engine, a camshaft and an arm member (rocker arm or swing arm) driven by the camshaft to drive a valve of an intake / exhaust system are provided. In the swing arm, a clearance adjustment screw and a lock nut for adjusting the valve clearance are provided at the fulcrum, and in the rocker arm, a clearance adjustment screw and a lock nut that abut on the top of the valve stem are provided at one end thereof. Is provided.

As a countermeasure against thermal expansion occurring in a cylinder head, a valve stem and the like during use of an engine, a valve clearance of about 100 μm is set in an engine assembly line. Conventionally, when setting the valve clearance by the manual method, insert a gap gauge of the same thickness as the set valve clearance between the arm member and the cam or valve, and use a screwdriver to set the clearance adjustment screw. Tightening the clearance adjustment screw and then tightening the lock nut while estimating the tightening torque with the sense of a hand so that the valve does not open.

On the other hand, in the valve clearance setting method described in Japanese Patent Application Laid-Open No. 5-35243, a cam shaft is stopped at a valve closed position, an open end of a port corresponding to the valve is closed, and a predetermined amount is set in the port. Supply the pressurized air, and then slightly move the clearance adjustment screw to the valve open side, and after the air pressure in the port drops to the set pressure, rotate the clearance adjustment screw in the opposite direction to the above by a predetermined amount of rotation. It describes a method of setting the valve clearance by simply rotating the valve. The predetermined rotation amount corresponds to a sum of a predetermined valve opening amount (which is obtained in advance) when the air pressure in the port is a predetermined pressure and a predetermined valve clearance. This valve clearance setting method is implemented through an automated and dedicated complicated device, and in this method, a clearance gauge is not used.

[0005]

According to the manual valve clearance setting technique, the skilled worker adjusts the tightening torque when tightening the clearance adjusting screw while estimating it with the sense of a hand.
There is a problem that an error of about μm occurs, an error of the valve clearance increases, adversely affects the performance of the engine, and it takes a lot of labor and time because a skilled worker performs trial and error. .

In the valve clearance setting method described in the above publication, the clearance adjusting screw is tightened to the valve opening side to attain the predetermined valve opening amount, and thereafter the clearance adjusting screw is returned to the valve closing side by a predetermined rotation amount. So
The adjustment operation of the clearance adjustment screw is two steps,
The movement amount of the clearance adjusting screw also increases. That is, assuming that the predetermined valve opening amount is 50 μm and the set valve clearance is 100 μm, (50 + α) μm (where α
Moves the clearance adjustment screw toward the valve opening side by the amount of movement of the clearance adjustment screw until the valve starts to open), and then moves the clearance adjustment screw toward the valve closing side by (50 + 100) μm. As a result, adjustment of the adjustment screw becomes complicated, and waste increases.

In order to drive the clearance adjustment screw toward the valve closing side by the predetermined amount of rotation, it is necessary to apply a dedicated and automated adjustment screw drive mechanism, which is disadvantageous in equipment cost. This valve clearance setting technique is also common to the conventional manual valve clearance adjustment technique in that the set valve clearance is adjusted after the valve is fully closed. The purpose of the present invention is
In the method of adjusting the valve clearance, it is necessary to improve the accuracy of the adjustment of the valve clearance, to simplify the adjustment work of the valve clearance adjusting screw, to eliminate the need for skill, and to increase the work efficiency.

[0008]

According to a first aspect of the present invention, there is provided a method of adjusting a valve clearance, comprising: a first step of stopping a camshaft of a valve operating system of an engine at a position where a valve is fully closed; A second step of supplying a pressurized gas of a predetermined pressure into the port with the open end of the port corresponding to the valve sealed with a sealing member, and then driving the valve by sliding contact with the cam of the camshaft. A third step of inserting a gap gauge having a predetermined thickness larger than the set valve clearance between the arm member and the cam or the valve to be closed, and then moving the retracted valve clearance adjusting screw toward the valve closed side to the gas pressure in the port. And a fourth step of adjusting the valve to the valve open side until the pressure decreases to a set value.

The present invention is based on the principle that when a pressurized gas of a predetermined pressure is supplied to a port, the gas pressure in the port decreases to a gas pressure corresponding to the valve opening amount. Further, the present invention uses a clearance gauge having a predetermined thickness larger than the set valve clearance, and adjusts a valve clearance adjusting screw so as to have a valve opening amount corresponding to the predetermined thickness. This is based on a technical idea of setting a valve clearance corresponding to the sum of the above.

In a state where a pressurized gas of a predetermined pressure is supplied into the port and a gap gauge having a predetermined thickness larger than the set valve clearance is inserted, the valve clearance adjusting screw which is retracted to the valve closing side in the fourth step is When the valve is adjusted to the valve open side until the gas pressure in the port decreases to the set value, the valve opening amount corresponding to the set value is obtained. Since the predetermined thickness is determined in advance so as to be equal to the valve opening amount, when the adjustment of the valve clearance adjusting screw is completed, the valve is opened by an amount corresponding to the predetermined thickness, and the set valve clearance is set. And a predetermined thickness is set.

Then, with the clearance gauge removed,
The valve that is biased to close by the valve spring is fully closed, and the valve clearance becomes the set valve clearance. The first to fourth steps can be performed by a manual method, or can be performed by a dedicated device. In particular, the adjustment of the valve clearance adjustment screw in the fourth step is as follows.
It can be done manually or with an automatic screwdriver.

According to a second aspect of the present invention, in the first aspect of the present invention, the pressure of the pressurized gas of a predetermined pressure previously supplied into the port before the first step is changed when the valve opening amount of the valve is changed. The pressure change characteristics are obtained experimentally, and the predetermined thickness and the set pressure are determined based on the gas pressure change characteristics. When a pressurized gas of a predetermined pressure is supplied into the port and the opening amount of the valve is increased, the gas pressure in the port decreases in accordance with the increase in the opening amount. Since the gas pressure change characteristic changes when the diameter of the valve changes, the gas pressure change characteristic is experimentally obtained in advance, and the predetermined thickness and the set pressure are determined based on the gas pressure change characteristic. Thus, the valve clearance can be set with high accuracy.

According to a third aspect of the present invention, in the second aspect, the predetermined thickness and the set pressure are determined based on the linear region of the gas pressure change characteristic. Since the gas pressure change characteristic includes a linear region and a curved region, the predetermined thickness and the set pressure are determined based on the linear region of the gas pressure change characteristic. In the linear region, for example, when pressurized air is used as a pressurized gas with a valve diameter of about 30 mm, the change in gas pressure per 10 μm of change in valve opening is about 0.1 kg / cm ^2. Therefore, the valve clearance adjusting screw can be adjusted with high accuracy by measuring the set pressure through a pressure gauge having a scale of about 0.02 Kg / cm ² or a finer scale. Further, since a plurality of sets of the predetermined thickness and the set pressure can be obtained from the linear region of the gas pressure change characteristic, the convenient predetermined thickness and the set pressure can be applied.

According to a fourth aspect of the present invention, in the third aspect of the present invention, after the fourth step, the lock nut for locking the valve clearance adjusting screw is tightened, the clearance gauge is removed, and the supply of the pressurized gas is stopped. The sealing by the stop member is released. By tightening the lock nut, the valve clearance adjustment screw can be locked so as not to be loosened, the gap gauge is pulled out, the supply of pressurized gas is stopped, and the sealing by the sealing member is released, so the cylinder head Can be sent to the next step.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. First, the intake / exhaust system and the valve train of the cylinder head of the engine will be briefly described. As shown in FIG. 1, this cylinder head 1 is a cylinder head of an in-line four-cylinder engine, and one cylinder head is provided for each cylinder.
Exhaust valves 2 and two intake valves 3 are provided,
The exhaust port 4 is opened to the left side of the cylinder head 1,
The intake port 5 is open to the right inclined side surface of the cylinder head 1. On the left side on the open end side of the exhaust port 4, a stud bolt 6 for mounting an exhaust manifold is planted, and on the right inclined side on the open end side of the intake port 5, a stud bolt 7 for mounting an intake manifold is planted. Has been established.

An exhaust valve 2 for opening and closing the rear end of the exhaust port 4 and an intake valve 3 for opening and closing the rear end of the intake port 5 are provided so as to be able to move up and down in a vertical position. 2b, the valve stem 3a of the intake valve 3 is guided by the valve guide 3b, the exhaust valve 2 is urged to the closing side by the valve spring 9 received by the spring receiver 8, and the intake valve 3 is received by the spring receiver. The valve spring is biased to the closing side.

A camshaft 10 extending in the direction perpendicular to the paper is provided at the center of the upper end of the cylinder head 1 in the width direction. The camshaft 10 is rotatably supported by a plurality of bearing portions and bearing caps 11. I have. The camshaft 10 has a cam 1 corresponding to each of the valves 2 and 3.
1 are formed, and the swing arms 1 corresponding to the respective cams 11 are formed.
2 are provided. In the case of the illustrated exhaust valve 2 as an example, an intermediate portion of the swing arm 12 is in sliding contact with the cam 11, and a valve clearance adjusting screw 13 (hereinafter, referred to as an adjusting screw) is screwed to a fulcrum side end of the swing arm 12. The hemisphere at the lower end of the adjusting screw 13 is pivot 1
5, a lock nut 14 is screwed onto the adjusting screw 13, and the other end of the swing arm 12 opposite to the fulcrum end is connected to the valve stem 2 of the exhaust valve 2.
a is in contact with the upper end.

The two intake valves 3 are also opened and closed by the same swing arms (not shown) as described above. The cylinder head 1 is sequentially conveyed from two sides of a roller conveyor 17 on a conveyance table 16 of a cylinder head assembly line from the near side of the sheet of FIG. 1 to the rear of the sheet. next,
A valve clearance adjusting device for adjusting the valve clearance of the cylinder head 1 will be described. As the valve clearance adjustment devices, four sets of valve clearance adjustment devices 20 for four exhaust valves 2 for four cylinders and eight sets of valve clearance adjustment devices 20A for eight intake valves 3 are provided. However, a description will be given with reference to FIG. 1 using a set of valve clearance adjusting devices 20 as an example.

This valve clearance adjusting device 20 includes:
A sealing member 21 for sealing the open end of the exhaust port 4 so as to be openable and closable in a gas-tight manner; and a plurality of members for driving the sealing member 21 between a sealing position shown by a solid line and an open position shown by a chain line. A dynamic air cylinder 22 and an air supply / discharge device (not shown) for supplying and discharging pressurized air to and from the air cylinder 22
, A support member 23, a pressurized air supply system 24, a pressure gauge 25 for measuring an air pressure in the exhaust port 4, and a gap gauge 2.
6 and a screwdriver 27 and the like.

A rubber plate 21a is fixed to the surface of the sealing member 21 on the cylinder bed 1 side, and a plurality of bolt holes 21b through which a plurality of stud bolts 6 are loosely inserted are formed in the sealing member 21. An air passage 21 c that receives pressurized air at a predetermined pressure (for example, 0.5 kg / cm ² G) from the pressurized air supply system 24 and supplies the pressurized air into the exhaust port 4 is also formed. The air cylinder 22 is fixed to a support member 23. When the piston rod is extended, the sealing member 21 is at a sealing position, and when the piston rod is retracted, the sealing member 21 is at an open position.

About 4 to 5K for the pressurized air supply system 24
A pipe 29 extending from a pressurized air source 28 for supplying pressurized air of g / cm ² G is provided with an on-off valve 33 and a regulator 30 for reducing the air pressure of the pressurized air to the predetermined pressure.
The outlet of the regulator 30 is connected to an air passage 21 c of the closing member 21 via an air hose 31. A connection fitting 32 for connecting the pipe 29 and the air hose 31 is fixed to the support member 23 by a fitting 23a. The pressure gauge 25 is attached to the sealing member 21.
5 is connected to the air passage 21c by an air passage 25a formed in the sealing member 21. Although FIG. 1 also shows the valve clearance adjusting device 20A, the description is omitted because it has the same configuration.

Next, a method of adjusting the valve clearance of the exhaust valve 2 using the above-described valve clearance adjusting device 20 will be described. First, in a preparatory stage before the cylinder head 1 of this type is put into an assembly line, the air pressure change characteristic shown in FIG. 2 is obtained in advance by using the valve clearance adjusting device 20 outside the assembly line. In this case, first, the camshaft 10
The base circle of the cam 11 is brought into contact with the swing arm 12 (that is, the exhaust valve 2 is fully closed) to fix the camshaft 10, and the adjusting screw 13 is adjusted so that the valve clearance becomes zero. The member 21 is closed, and the predetermined pressure (0.
5 Kg / cm ² G) of pressurized air is supplied. Initially, the opening amount of the exhaust valve 2 (the descending distance from the fully closed position) is zero, and the air pressure does not decrease.

Next, when a gap gauge 26 having a thickness of 5 μm is inserted between the cam 11 and the swing arm 12, the exhaust valve 2 is opened by 5 μm, so that the air pressure in the exhaust port 4 is slightly reduced. The air pressure is precisely measured, and the thickness of the gap gauge 26 and the air pressure are recorded. Then, while measuring and recording while sequentially increasing the thickness of the gap gauge 26 by 5 μm, and plotting the recorded data on paper, the air pressure change characteristic shown in FIG. 2 is obtained. The air pressure change characteristics include a curved area Ca, a linear area Cb, and a curved area Cc, and the valve diameter of the exhaust valve 2 is 30.4 m.
m, the inclination of the linear region Cb is 10 μm
The change in air pressure per contact is 0.1 kg / cm ² G. Therefore, when the linear region Cb of the air pressure change characteristic is used, for example, if the reading error of the air pressure measured by the pressure gauge 25 is ± 0.02 Kg / cm ² G, the valve opening amount is ± 2 μm. Only an error of

Next, the cylinder head 1 of the above-described model is put into an assembly line, and in the assembling step of actually assembling the cylinder head 1, the valve clearance adjusting device 20 is used to control the valve of the exhaust valve 2 of the first cylinder. A method for adjusting the clearance will be described. When the cylinder head 1 flows into the valve clearance adjustment station of the assembly line, in a first step, the camshaft 10 is stopped at a position where the exhaust valve 2 is fully closed and held at that position. Then, the adjusting screw 13 is set in a state of being sufficiently retracted to the exhaust valve closing side. In this state, the exhaust valve 2 is fully closed.

Next, in the second step, the air cylinder 2
The piston rod of No. 2 is extended, the sealing member 21 is brought into contact with the left side surface of the cylinder head 1, and the opening end of the exhaust port 4 is sealed by the sealing member 21 in a gas-tight manner. And
Open the on-off valve 33 to open the air passage 2 from the pressurized air supply system 24.
1c, pressurized air is supplied into the exhaust port 4 to reduce the air pressure in the exhaust port 4 to the predetermined pressure (0.5 kg / cm ^2).
G). Next, in a third step, the set valve clearance VC is set between the swing arm 12 and the cam 11.
(For example, VC = 100 μm), a gap gauge 26 (for example, d = 35 μm) thicker than the gap gauge 26 (for example, d = 35 μm).
(Thickness of 135 μm). Also in this state, the exhaust valve 2 is fully closed, and the air pressure in the exhaust port 4 is the predetermined pressure.

Next, in a fourth step, the adjusting screw 13 is adjusted to the exhaust valve open side using the screw driver 27, and the air pressure in the exhaust port 4 is adjusted to the set pressure Pa ( For example, the adjustment screw 13 is adjusted to the exhaust valve open side until the pressure drops to 0.34 kg / cm ² G). Here, the predetermined thickness d and the set pressure Pa are determined based on the linear region Cb of the air pressure change characteristic as shown in FIG. In the state after this adjustment, the exhaust valve 2
Is equal to the predetermined thickness d, and a gap gauge 26 having a thickness of (VC + d) is inserted between the cam 11 and the swing arm 12.

Next, in the fifth step, when the lock nut 14 is tightened using a nut fastener (not shown), the valve clearance adjustment for the exhaust valve 2 is completed. Then, the gap gauge 26 is removed, the on-off valve 33 is closed, the supply of the pressurized air is stopped, the piston rod of the air cylinder 22 is retracted, and the closing member 21 is switched to the open position. When the clearance gauge 26 is removed, the exhaust valve 2 is switched to the fully closed position by the urging force of the valve spring 9, and the valve clearance becomes the set valve clearance VC.

Thereafter, the second, third, and fourth cylinder exhaust valves 2
Adjust the valve clearance in order, and then
For each of the two intake valves 3 of the first to fourth cylinders,
After adjusting the valve clearance in the same manner as in the first to fifth steps, the cylinder head 1 is transported to the next station. However, air pressure change characteristics similar to the air pressure change characteristics are obtained in advance for each of the two types of intake valves 3, and the predetermined thickness and the set pressure are determined based on those characteristics.

In the above-described method of adjusting the valve clearance, the moving amount of the adjusting screw 13 is converted into the air pressure in the exhaust port 4 instead of directly adjusting the moving amount of the adjusting screw 13 with the hand. Since the adjustment can be performed while checking the air pressure measured by the pressure gauge 25, the accuracy of adjusting the valve clearance can be improved. Further, even if a slight error occurs with respect to the set value Pa of the air pressure when the adjustment of the adjusting screw 13 is completed, only a small error occurs in the valve clearance, so that the accuracy of the valve clearance adjustment can be improved. Further, the adjustment of the valve clearance is simplified, and the adjustment can be efficiently and reliably performed even by a non-expert. When adjusting the adjusting screw 13, it is only necessary to adjust the exhaust valve open side in one direction until the air pressure in the exhaust port 4 decreases to the set value Pa.
Adjustment is simplified and no waste occurs.

That is, instead of adjusting the valve clearance to the set valve clearance with the exhaust valve 2 fully closed as in the prior art, the exhaust valve 2 is set to a predetermined thickness d.
The valve is opened by an amount equal to, the air pressure in the exhaust port 4 can be reduced from the initial predetermined pressure, and the valve clearance of the sum of the set valve clearance VC and the predetermined thickness d is set. The adjustment of the screw 13 is simplified.

Further, the adjustment for the adjusting screw 13 can be manually adjusted by the screw driver 27, which is advantageous in terms of equipment cost. Further, the air pressure change characteristics shown in the figure are experimentally obtained in advance, and the predetermined thickness d and the set pressure Pa are determined based on the linear region Cb of the air pressure change characteristics, thereby increasing the valve clearance. It is possible to set the accuracy. Then, since the plurality of sets of the predetermined thickness d and the set pressure Pa can be obtained from the linear region Cb of the air pressure change characteristic, the convenient predetermined thickness d and the set pressure Pa can be applied. .

Here, a description will be given of a modification in which the above-described embodiment is partially modified. 1) In the valve clearance adjusting device 20, instead of the screwdriver 27, a fastening machine that can automatically or semi-automatically tighten the adjusting screw 13 and the lock nut 14 is applied. An air pressure measuring device that outputs a pressure signal may be applied to the apparatus, and the fastening machine may be controlled using a detection signal of the air pressure measuring device. By applying such a configuration, a valve clearance adjusting device that operates automatically may be provided.

2) In the third step, the gap gauge 26
May be inserted between the swing arm 12 and the upper end surface of the valve stem 2 a of the exhaust valve 2 instead of inserting the gap gauge between the cam 11 and the swing arm 12. The present invention is similarly applicable to a case where the valve train has a rocker arm.

3) Although deviating from the gist of the present invention, in the air pressure change characteristics of FIG. 2, the predetermined pressure (initial pressure) is set sufficiently high, and the exhaust valve opening amount is equal to the set valve clearance. A linear region of the air pressure change characteristic can be obtained in the range, and the valve clearance can be adjusted without using a gap gauge. In this case, in the air pressure change characteristic, a set pressure corresponding to the valve clearance when the exhaust valve opening amount is equal to the set valve clearance is obtained in advance, and when adjusting the adjustment screw 13 in the fourth step, the pressure in the exhaust port 4 is adjusted. The adjusting screw 13 may be adjusted to the exhaust valve open side until the air pressure decreases to the set pressure corresponding to the valve clearance.

[0035]

According to the first aspect of the present invention, the amount of movement of the valve clearance adjusting screw is converted into the gas pressure in the port, instead of adjusting the amount of movement of the valve clearance adjusting screw directly by hand. Since the gas pressure can be adjusted while checking the gas pressure displayed on the pressure gauge, etc., and even if a slight error with respect to the set value of the gas pressure occurs when the adjustment of the valve clearance adjustment screw is completed, a minute error in the valve clearance will occur. Since this only occurs, the accuracy of the adjustment can be increased. The adjustment of the valve clearance is simplified, and the adjustment can be performed efficiently and reliably even by a non-expert. When adjusting the valve clearance adjusting screw in the fourth step, it is only necessary to adjust the valve pressure in the one direction toward the valve opening side until the gas pressure in the port drops to the set value. Does not occur.
Since the adjustment for the valve clearance adjusting screw can be manually adjusted with a screw driver or the like, it is advantageous in terms of equipment cost.

According to the second aspect of the invention, in addition to the effect of the first aspect, as described above, the gas pressure change characteristics are experimentally obtained in advance, and the predetermined thickness is determined based on the gas pressure change characteristics. By determining the pressure and the set pressure, the valve clearance can be set with high accuracy.

According to the third aspect of the invention, in addition to the effect of the second aspect, the predetermined thickness and the set pressure are determined based on the linear region of the gas pressure change characteristic, so that the valve clearance adjusting screw can be adjusted. Adjustment can be performed with high accuracy.
Further, since a plurality of sets of the predetermined thickness and the set pressure can be obtained from the linear region of the gas pressure change characteristic, the convenient predetermined thickness and the set pressure can be applied.

According to the fourth aspect of the invention, in addition to the effect of the third aspect, by tightening the lock nut, the valve clearance adjusting screw can be locked so as not to be loosened. Since the supply of the pressurized gas is stopped and the sealing by the sealing member is released, the cylinder head can be sent to the next step.

[Brief description of the drawings]

FIG. 1 is a cross section of a cylinder head and a valve clearance adjusting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing air pressure change characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Exhaust valve 3 Intake valve 4 Exhaust port 5 Intake port 10 Camshaft 11 Cam 12 Swing arm 13 Valve clearance adjustment screw 14 Lock nut 21 Sealing member 24 Pressurized air supply system 25 Pressure gauge 26 Gap gauge 27 Screw driver

Claims (4)

[Claims] 1. A first step of stopping a camshaft of a valve train of an engine at a position for fully closing a valve, and then closing an open end of a port corresponding to the valve in a cylinder head with a sealing member. A second step of supplying a pressurized gas of a predetermined pressure into the port in a stopped state, and then a valve clearance between the cam or the valve and an arm member that slides on the cam of the cam shaft to drive the valve. A third step of inserting a gap gauge thicker by a predetermined thickness, and a fourth step of adjusting the valve clearance adjustment screw in the retracted state to the valve closed side to the valve open side until the gas pressure in the port decreases to the set value. A method for adjusting a valve clearance, comprising the steps of: 2. Prior to the first step, a gas pressure change characteristic of the pressurized gas of a predetermined pressure supplied into the port when the valve opening amount of the valve is changed is previously determined experimentally. The method according to claim 1, wherein the predetermined thickness and the set pressure are determined based on a gas pressure change characteristic. 3. The method according to claim 2, wherein the predetermined thickness and the set pressure are determined based on a linear region of the gas pressure change characteristic. 4. After the fourth step, a lock nut for locking a valve clearance adjusting screw is tightened, a gap gauge is removed, supply of pressurized gas is stopped, and sealing by a sealing member is released. The method for adjusting valve clearance according to claim 3.