How to Check and Adjust Valve Clearance

Question 1: Briefly describe the adjustment steps of valve clearance? There are two common methods to check and adjust the valve clearance:

One is the cylinder-by-cylinder adjustment method, that is, according to the ignition sequence of the cylinder, the gap between the intake valve and the exhaust valve of the cylinder can be adjusted after the piston of the cylinder is determined to be at the compression top dead center position; After adjustment, turn the crankshaft and gradually adjust the valve clearance of other cylinders according to this method.

Second, the method of twice adjustment is adopted, that is, the crankshaft is rotated to make the piston of the first cylinder at the compression top dead center, and the flywheel mark is aligned with the inspection hole mark line (such as EQ6 100 engine). At this time, the valves of 1, 2, 4, 5, 8 and 9 can be adjusted (referring to the sequence of engine valves from front to back); Then turn the crankshaft once, so that the six-cylinder piston is at the top dead center of the compression stroke, and then adjust 3, 6, 7, 10 "plus two valves (i.e. 1 1, 12), which is actually memory adjustment. When adjusting, while tightening the adjusting screw, insert the thickness gauge between the valve stem end and the rocker arm and pull it back and forth. If you feel slight resistance, check it again until it is suitable. The cylinder-by-cylinder method requires the crank to rotate the crankshaft more times, and the inspection and adjustment time is longer. However, for the seriously worn engine, the cylinder-by-cylinder method is more accurate to check and adjust the valve clearance.

Adjusting the valve clearance twice saves time and effort, but it is difficult for maintenance personnel to remember the different adjustable valve serial numbers of different models, which is more complicated.

Question 2: How to adjust the valve clearance of an automobile There are two common methods to adjust the valve clearance:

One is the cylinder-by-cylinder adjustment method, that is, according to the ignition sequence of the cylinder, the gap between the intake valve and the exhaust valve of the cylinder can be adjusted after the piston of the cylinder is determined to be at the compression top dead center position; After adjustment, turn the crankshaft and gradually adjust the valve clearance of other cylinders according to this method.

Second, the method of twice adjustment is adopted, that is, the crankshaft is rotated to make the piston of the first cylinder at the compression top dead center, and the flywheel mark is aligned with the inspection hole mark line (such as EQ6 100 engine). At this time, the valves of 1, 2, 4, 5, 8 and 9 can be adjusted (referring to the sequence of engine valves from front to back); Then turn the crankshaft once, so that the six-cylinder piston is at the top dead center of the compression stroke, and then adjust 3, 6, 7, 10 "plus two valves (i.e. 1 1, 12), which is actually memory adjustment. When adjusting, while tightening the adjusting screw, insert the thickness gauge between the valve stem end and the rocker arm and pull it back and forth. If you feel slight resistance, check it again until it is suitable.

The cylinder-by-cylinder method requires the crank to rotate the crankshaft more times, and the inspection and adjustment time is longer. However, for the seriously worn engine, the cylinder-by-cylinder method is more accurate to check and adjust the valve clearance. Adjusting the valve clearance twice saves time and effort, but it is difficult for maintenance personnel to remember the different adjustable valve serial numbers of different models, which is more complicated.

Question 3: How to judge the large valve clearance? How long does it take to adjust the valve clearance? You can obviously hear the sound of the valve "click", which is very clear when idling, but you can't hear it when it becomes continuous after refueling. The valve can't be adjusted too tightly, so it's not easy to hit the car, and the car doesn't idle, which is easy to cause valve ablation and engine oil burning. Therefore, it is better to be restless than small, and you can hear the weak valve ring instead of adjusting it too tightly.

Question 4: What should I pay attention to when checking and adjusting the valve clearance? This requires turning the adjusted disc to the piston top dead center.

Question 5: Briefly describe the purpose and significance of engine valve clearance inspection and adjustment? Inspection and adjustment of motor valve clearance is an important work content.

During the engine operation, the wear or looseness of the valve train parts or the expansion of the valve due to the temperature rise will lead to the change of the original valve clearance. Except for the engine with hydraulic cylinder valve mechanism (the length of which can be automatically adjusted by oil pressure and the thermal expansion of the valve can be compensated at any time), there is no need to adjust the valve clearance. When other engines are driven 10000 km for secondary maintenance, check and adjust the valve clearance to meet the technical requirements. ?

The size of the valve clearance has a great influence on the performance of the engine in all aspects: if the clearance is too small, the engine may leak air due to the expansion of the valve stem in the hot state, resulting in power reduction and even burning out the valve; If the clearance is too large, the collision between the transmission parts and between the valve and the valve seat will easily occur. At the same time, the duration of valve opening will be reduced and the intake and exhaust will be insufficient, which will also directly affect the normal operation of the engine. Therefore, in order to ensure the normal operation of the engine, the valve clearance must be adjusted.

Question 6: What is the inspection method of valve clearance? In all kinds of engines, the valve clearance will become smaller due to the wear of the valve slope and valve seat; Because the valve stem tail end, rocker arm head, adjusting screw, push rod head, tappet and cam are worn, the clearance will become larger. In addition, the looseness of the fixed nut of the rocker arm seat, the replacement of the cylinder pad, the tightening of the cylinder head nut and the disassembly and assembly of the valve train will all cause the change of the valve clearance. Therefore, the valve clearance must be checked and adjusted regularly as needed. The inspection method of valve clearance is as follows: shake the crankshaft to make the valve to be inspected in a completely closed state (top dead center of compression stroke and exhaust valve in a closed state), insert the gauge between the tail of the valve stem and the rocker arm end, and pull the gauge back and forth to feel a little resistance, and the thickness of the gauge is the valve clearance value. The valve clearances of common internal combustion engines are as follows: intake valve and exhaust valve of the following models: intake valve and exhaust valve of the following models: 4125a 0.300.35j2850.30 ~ 0.350.35 ~ 0.40415t0.400. ~ 0.250 . 25 ~ 0.30 lr 4 1050.3 ~ 0.40 . 4 ~ 0.5 LD 375 q 0.20 ~ 0.250 . 25 ~ 0.30 lr 6 1050.3 ~ 0.40 . 4 ~ 0.5s 1 1 100.30 ~ 0.400.40 ~ 0.50 lr 46438

Question 7: How to adjust the valve clearance? Valve clearance refers to the clearance between the end face of the valve rod and the end face of the valve clearance adjusting screw when the engine is cooled (that is, below 35 degrees) and the valve is completely closed. When the engine is working, the valve stem expands and stretches when heated, which makes the valve clearance smaller. Due to the deformation of the cylinder head, the center of the valve rocker arm seat is raised, which makes the valve clearance larger. When the cylinder head is cast iron, the thermal expansion coefficient is basically the same as that of the valve, and the working temperature of the valve is more than 1 times higher than that of the cylinder head. Therefore, the elongation of the valve stem is larger than that of the rocker arm seat in the hot state, and the valve clearance in the hot state is smaller than that in the cold state. Because the valve and transmission mechanism expand after the engine works, the valve is improperly closed. Even the engine can't work. There is a certain gap between the end face of the valve stem and the transmission part, which can compensate the expansion of the valve after heating and form a good seal between the valve and the valve seat. Influence of working temperature of parts on valve clearance. In the process of valve work and exhaust, the temperature of the engine is very high, but it is not high in the process of intake and compression, and it has certain heat dissipation and cooling effect through the cylinder head. Therefore, the average temperature of the valve is about twice that of the cylinder head. When the valve rocker arm is installed on the cylinder head, the temperature of the cylinder head is higher than the temperature of the lubricating oil, which is generally estimated by the temperature of the spark plug gasket, which is about 120 degrees. Influence of cylinder head expansion on valve clearance When the cylinder head expands, the cylinder head rises and the center of the rocker shaft also rises, which increases the valve clearance, but the valve seat in the cylinder head is also expanding. The center of the rocker arm shaft is lowered, so the total elevation is smaller than the rocker arm seat on the cylinder head, such as the water-cooled engine of Honda CH 125 Shark Motorcycle 152M 1. The distance from the bottom of the cylinder head to the center of the rocker shaft is the calculated length in the expansion direction. If compared with the valve elongation, subtract the height from the bottom surface to the valve center (in general, the length of the rocker shaft center in the expansion direction is greater than the valve length). Influence of temperature change of lower camshaft valve train on valve train. The thermal expansion of transmission parts such as valve push rod and tappet makes the valve clearance smaller, and the total length of these transmission parts becomes longer. Although the temperature rise is not great, it will also have an impact. Most parts and cylinder heads of motorcycle engines are made of aluminum. In the heating state, the lifting amount of the valve rocker center is greater than the valve elongation. Because the long arm of the rocker arm is on the valve side, the change of the center of the rocker arm shaft is amplified. Therefore, the aluminum cylinder head has a small valve clearance when it is cold and a large valve clearance when it is hot. In most motorcycle engines, the air-cooled valve clearance is about 0.05-0.1mm. In some engines, the valve clearance is 0 mm For example, the valve clearance of CG motorcycle air-cooled 157FMI engine is only 0-0.02 mm. Because the engine works at high temperature, high speed and high load, the valve clearance will inevitably change with time, thus affecting the normal work of the engine. Too large or too small valve clearance mainly has the following hazards: a) too large valve clearance will make the valve timing open late and close early, that is, the valve opening time will be shortened. 1) In the intake stroke, due to insufficient valve opening time, the intake air volume of the combustible mixture valve decreases, the inflation coefficient of the engine decreases, and the engine power cannot be fully exerted. 2) During the exhaust stroke, poor exhaust and insufficient inflation increase fuel consumption, increase engine temperature, reduce power and make the valve knock loudly. B) If the valve clearance is too small, the valve timing will be opened in advance and closed later, that is, the valve opening duration is too long. 1) will cause air leakage due to lax valve closure, reduce effective compression ratio and reduce engine power. In severe cases, it will also cause a lot of carbon deposition and ablation of the valve, which will lead to the cylinder not working normally. 2) Incomplete combustion, power reduction and exhaust valve shooting. The size of valve clearance is usually determined by the manufacturer according to the performance characteristics of the engine, and the values of different models are different because of the different materials and structures. A) Check and adjust the valve clearance so that the engine is at the end of the compression stroke, that is, when the piston in the cylinder to be tested is at the top dead center position. First, open the cylinder head cover, remove the large and small bolts on the left crankcase, and turn the crankshaft with a special sleeve so that the T-shaped left notch on the flywheel rotor is aligned with the alignment mark of the left box cover. At this time, it should be confirmed that the valve is not pressed down, otherwise, the crankshaft should rotate for another turn to realign the timing mark. B) Insert the feeler gauge between the valve clearance adjustment screw and the valve stem end for inspection. When adjustment is needed, loosen the lock nut on the valve rocker arm and insert the feeler gauge of the middle value of the standard clearance at the measuring position. If the specified clearance is 0.06-0. 1 mm, insert a feeler gauge of 0.08mm.. Turn the valve clearance adjusting screw with special tool ... >>

Question 8: What is the method of adjusting the valve clearance twice? Turn the engine twice and all valves can be adjusted.

Question 9: How to adjust the valve and judge the clearance between the rocker arm and the valve? Isn't there a mark on the crankshaft pulley? Shake him to align with the mark on the cylinder! That's the top dead center of a cylinder, and then rotate the crankshaft 360 degrees in the direction of engine rotation! That's the top dead center of four cylinders! You should know that the top dead center of these two cylinders can be adjusted by other cylinders!