China Naming Network - Solar terms knowledge - How to adjust the valve clearance of SD4AW604u engine of Yellow Sea pickup truck?

How to adjust the valve clearance of SD4AW604u engine of Yellow Sea pickup truck?

1. Valve clearance: When the valve is completely closed, the clearance between the end of the valve rod and the parts of the valve train is called valve clearance.

Second, the necessity of valve clearance:

When the engine is working, the valve will expand due to the increase of temperature. If there is no gap between the valve and its transmission parts in the cold state or the gap is too small, the expansion of the valve and its transmission parts in the hot state will inevitably lead to the untidy closing of the valve, resulting in air leakage during the compression and power stroke of the engine, which will reduce the power and even make it difficult to start in serious cases. In order to eliminate this phenomenon, the engine usually leaves a valve clearance when it is assembled in cold state to compensate for the expansion of the valve after heating. Some engines use hydraulic tappets, the length of which can be changed automatically, and the thermal expansion of the valve can be compensated at any time, so there is no need to reserve the valve clearance.

Third, the valve clearance is too large and too small.

The valve clearance is determined by the engine manufacturer according to the test. Generally, in the cold state, the intake valve clearance is 0.25mm~0.35mm, and the exhaust valve clearance is 0.30mm~0.35mm.

1, too small: the valve clearance is too small, and the engine may leak air when the valve is not tightly closed in hot state, resulting in power reduction and even burning the valve.

2. Too large: too large valve clearance will cause impact noise between transmission parts and between valve and valve seat, which will accelerate wear. At the same time, it will also reduce the duration of valve opening, and the inflation and exhaust of the cylinder will become worse.

Fourth, the valve clearance adjustment method

1. Draw a line every 4mm in the radial direction of the valve working face, so that the matching valve can contact with the valve seat. Turn the valve 1/8 ~ 1/4 and take it out. If the pencil line trace has been completely interrupted and the contact is below the center, it means that the seal is good; If some lines are not broken, or the contact position is wrong, it means that the seal is not tight or not ideal and needs to be polished or repaired again.

2. After patting the valve several times on the mating seat, check the working faces of the valve and the valve seat, and a bright and complete halo should appear. The halo position on the valve should be below the center of the working cone, so it is considered that the sealing requirements have been met.

3. Check with the valve seal tester with barometer that the valve group parts are in the assembled state. Press the cylinder of the testing machine tightly at the position of the valve head, so that the joint surface between the end face of the container and the cylinder head (or cylinder block) can maintain a good seal. Then pinch the rubber ball and inflate the air container to make it have an air pressure of 0.6 ~ 0.7 MPa. If the barometer reading does not drop within half a minute, it means that the combination between the valve and the seat is well sealed.

Principles of checking and adjusting valve clearance

It should be done when the valve is completely closed and the valve tappet is lowered to the lowest position. The clearance between the end face of the valve stem and the rocker arm should be measured for overhead valves, and the clearance between the end face of the valve stem and the tappet should be measured for side valves. There are two inspection and adjustment methods.

Five, check the adjustment method

(a) cylinder by cylinder adjustment method.

First, find the compression end point of a cylinder, adjust the gap between the intake valve and the exhaust valve of the cylinder, and then crank the crankshaft one by one according to the ignition order.

(2) twice adjustment method.

Taking a six-cylinder engine with 1, 5, 3, 6, 2 and 4 ignition sequence as an example, the explanation is as follows:

① First, put the cylinder piston at the end of compression, and then the intake valve and exhaust valve of the cylinder must be adjustable.

(2) According to the principle of "two in three rows". That is, the intake valve of the second cylinder and the exhaust valve of the third cylinder must be completely closed at this time, and the adjustment can also be checked.

(3) Only one pair of valves can be adjusted at a time for two cylinders with connecting rod shaft diameters in the same plane, so the exhaust valves of five cylinders and the intake valves of four cylinders can also be checked and adjusted.

(4) When the six-cylinder piston is at the end of compression, the remaining valves that have not been checked and adjusted must be completely closed.

Therefore, all valves of the engine can be checked and adjusted by rotating the crankshaft twice.

(3) Other methods

(1) marking method.

Use a soft pencil to draw a line on the ground valve working surface every 8mm or so, then put the matching valve on the valve seat and rotate it 1/4 times. If all the drawn lines are cut off, it means good sealing. If some lines are not cut, it means that the sealing is poor and needs to be polished again.

(2) pressure method,

Inject 50 ml kerosene from the air inlet and the air outlet respectively, and then apply an air pressure of 20 ~ 30 kPa to see if there is kerosene oozing from the valve. If there is oil leakage, take it out and grind it again.

(3) coloring method,

Coating a layer of Gonglan film on the working surface of the valve, and rotating the valve relative to the valve seat when the valve naturally presses the valve seat. At this time, if the valve sealing surface 360. Gong blue appears, indicating that the valve is concentric, otherwise the valve should be replaced.

Excessive valve clearance will make the valve open late and close early. Therefore, the opening time is too short, and the combustible mixture can not be fully inhaled during the intake process. So that that normal pow of the engine cannot be exerted. In the exhaust process, the exhaust gas can not be fully discharged, which is easy to overheat the engine. In addition, when the engine is working, it will also produce valve knocking sound, which will affect the service life of the parts.

The valve clearance is too small, which leads to the early opening and late closing of the valve and makes the cylinder unable to work normally. With the increase of engine temperature, valves and valve seats will leak due to poor sealing. At the same time, it may also make the valve carbon deposit and even burn the valve.

(4) check the adjustment method

The general method of valve clearance adjustment is:

① Preheat the engine to make the cooling water temperature reach 80℃-90℃.

② Open the timing mark inspection holes on the clutch housing and cylinder head cover.

③ Confirm that the cylinder head bolts have been tightened to the specified torque.

④ Turn the crankshaft so that the "0" engraved line on the flywheel is aligned with the marking line on the clutch housing, and confirm that the cambered surface of the rocker arm of the intake and exhaust valve of the first cylinder is in contact with the base circle of the camshaft cam, that is, the piston of the first cylinder is at the compression top dead center (if the rocker arm is in contact with the cam, the crankshaft should rotate 360), and the valve is in the closed position.

⑤ Loosen the lock nut 2 of the adjusting screw 1 and turn the adjusting screw with a screwdriver to make the gap a between the lower end face of the screw and the upper end face of the valve stem 3 reach the specified value (determined by the thickness of the thickness gauge). Keep the screwdriver still, tighten the lock nut to the specified torque, and then insert the thickness gauge into the gap A for re-inspection so that the gap between the intake valve and the exhaust valve of the first cylinder can be adjusted.

⑥ Then turn the crankshaft clockwise (as viewed from the front of the engine). For a 4-cylinder engine, the valve clearance of the next ignition cylinder can be adjusted in the order of 1-3-4-2 every time it rotates 180. For a 3-cylinder engine, it can be adjusted according to the ignition sequence of 1-2-3 every 240 (the rotation angle of crankshaft can be converted by the number of teeth of flywheel ring gear).