1 Valve assembly points
The valve is composed of valve stem, valve head. The valve head is in direct contact with high temperature gas and has a high working temperature. In the work, the valve opening and closing frequently, and valve seat impact, and poor lubrication conditions, so the damage to the intake and exhaust valves is one of the main failures of diesel engines.
The valve should be tested before assembly: ① check the bending of the valve stem with a micrometer, the needle should not be more than 0.05 mm. or the valve stem on a flat plate rolling check, if bent, should be corrected or replaced. ② Measure the wear of the valve stem. Use a spiral micrometer to measure the upper, middle and lower parts of the valve stem. Usually compare the measurement results with the unworn part of the valve stem end. If it is more than 0. 05 mm, or if there is obvious stepped feeling when touching by hand, the valve should be replaced. ③ Check the valve length. If the end of the valve stem is worn unevenly, it should be repaired by grinding wheel, and the grinding amount should not exceed 0. 50 mm. ④ Check whether the working surface of the valve is grooved, widened and ablated due to wear, and spots and depressions appear, and if so, it should be polished.
When assembling the valves, pay attention to identify the markings of the intake and exhaust valves. ① structural features mark: for most engines, the diameter of the intake valve head is larger than the exhaust valve; valve cone angle is sometimes different, intake valve is sometimes 30 °, while the exhaust valve is often 4500 ② mark mark: some engines, intake and exhaust valves, both the diameter of the valve head or valve cone angle are the same. In order to distinguish between the factory in the exhaust valve head engraved with a mark. ② grinding mark. After grinding the valve, the valve head to use the steel character imprint to play the serial number (such as six-cylinder engine 12 valve head 1, 2 ......12, to the first cylinder of the first valve for 1, and then in order to mark), to ensure that each valve and its position with the grinding of the valve seat will not be installed wrong, so as to ensure that the valves and valve seat Sealing of each valve and valve seat.
2 Valve stem assembly points
The valve stem is cylindrical, the end is made into a cone or ring groove, some drilled with pin holes for the installation of locking plates, rings or pins, in order to fix the spring seat, to prevent the valve spring breakage or locking plates fall off when the valve falls into the cylinder and cause serious accidents. In operation, the valve stem moves in the valve guide. In order to make the valve accurately situated in the valve seat, does not occur left and right swaying skew and leakage, the valve stem and the catheter between the fit clearance is very small, the intake valve for 0.025 ~ 0. 077 mm, the wear limit clearance of 0.15 mm; exhaust valve for 0.040 ~ 0. 092 mm, the wear limit clearance of 0.15 mm. overhead valve valve distribution mechanism work, the valve chamber oil will be From the valve stem and valve guide clearance into the cylinder, resulting in carbon deposits in the cylinder, affecting the normal operation of the engine. In the valve stem part of the installation of rubber made of oil retaining ring, can reduce the valve chamber of the oil into the cylinder. Some engines are only installed in the intake valve stem oil ring, when the intake stroke, the vacuum generated in the cylinder will be the valve chamber of the oil through the valve stem and valve guide gap between the cylinder, installed oil ring, you can avoid excessive oil leakage into the cylinder and the adverse consequences. Therefore, when assembling the valve stem assembly, do not miss to install the valve locking plate, snap ring, oil retaining ring and other small parts.
3 Valve guide assembly points
Valve guide on the movement of the valve stem plays a guiding role, to prevent the valve head skewed, so that the valve and valve seat tight fit. The inner surface of the valve guide requires high dimensional accuracy. The valve guide tube is pressed directly into the cylinder head and plays a guiding role to ensure that the valve moves in a straight line. The outer diameter of the catheter and the catheter mounting holes on the cylinder head should have a certain degree of tightness, and the catheter should be pressed into the mounting holes on the cylinder head by hand during installation. If the hammering method is used to drive in, the upper end of the catheter should be padded with a wooden board to prevent the catheter from being deformed or damaged.
The outer circle of the catheter has no limit setting, when pressing the installation, pay attention to the depth of the press-in, that is, the upper end of the valve catheter should be a certain height above the cylinder head. You can measure the length of the exposed part of the old conduit, and leave the same length after the new conduit is loaded to ensure that the valve opening and closing activities of a sufficient distance. 195 diesel engine valve guide upper end of the distance above the cylinder head is 20 mm. If the upper end of the conduit above the cylinder head is too long, the spring seat and the valve guide collision, so that the valve can not be completely open, resulting in insufficient intake air, exhaust is not clean, and even make the valve push rod bending, breaking the rocker arm. Even bend the valve push rod and break the rocker arm. If the upper end of the tube is too short above the cylinder head, it will increase the resistance to intake and exhaust, and even cause valve leakage.
The valve guide has a chamfer at the top of the inner hole, for oil storage, supplying lubricating oil to the guide hole. Chamfer is too large, more oil storage, oil through the conduit hole into the cylinder burned off, increasing oil loss; chamfer is too small, insufficient oil supply, increasing the inner hole wear.
4 Valve spring assembly points
The function of the valve spring is to ensure that the valve and the valve seat of the close fit, generally each valve has two rotating opposite, set together in the inner and outer springs (double valve springs), in order to prevent the spring from *** vibration at work, even if one of the springs broken, the valve will not fall into the cylinder. The valve spring is attached to the valve stem, one end is supported on the cylinder head and the other end is supported on the spring seat. The spring seat is fixed in the ring groove at the end of the valve stem by a locking piece. The valve springs have sufficient spring force to overcome the inertial forces of the valves and other parts when the cam is turned, allowing the valves to quickly seat closed. When installing the valve assembly, the locking tabs must be installed correctly for the springs to fit securely.
Before installation, carbon should be removed, clean the parts, and then carefully check the parts for damage. And the valve spring to do the following tests: ① appearance test. After cleaning the valve spring, first of all, should be observed with the naked eye cracks, corrosion, skewed deformation, etc.. The above defects of the valve spring, should be replaced. ② free length inspection. Length generally available straightedge, calipers and depth gauge and other checks, but also can be used to check the length of the old and new spring comparison. When the length of the valve spring is found to be less than the standard size of 3 mm, generally should be replaced. ③ Stretch test. Check with a spring tester. Inspection of the spring according to the spring pressure to the working height, observe the reading of the tester, its elasticity should be in line with the specified value.
Installation, the installation order is the reverse of disassembly, but the same tools. The intake and exhaust valves into the cylinder head, and then the inner and outer valve springs pressed into the valve spring seat; installation of valve locking plate and valve springs, in order to ensure that the various conical surface fit, can be in the valve stem end of a set of tubes, the top of the locking plate, and then the side stand cylinder head, evenly knocking on the end of the casing for several times, so that the locking plate pressure flat bite. After installation, the valve locking plate must be located in the groove of the upper part of the valve stem, and should be higher or lower than the spring seat 0.7 ~ 2.5 mm. the height of the two locking plate should be the same, the gap between the two locking plate should be greater than 0.6 mm. measure the amount of valve subsidence, that is, the distance between the valve and the cylinder head plane. 195-type diesel valve subsidence is 1 ~ 1.8 mm. shake the spring seat with your hand, if the spring seat and the valve stem has a If the spring seat and the valve stem have a relative swing, then the spring seat or lock plate should be replaced