Diesel generator maintenance training diesel article -p35-p38 valve guide and valve...

Diesel generator maintenance training diesel article -p35-p38 valve catheter and valve stem wear

In the wear of the valve guide tube and the valve stem portion during a long-term relative movement, it is easy to increase the fitting clearance between the two. Under normal conditions, the clearance between the intake valve and the guide tube is approximately 0.09 mm, and the clearance between the exhaust valve and the guide tube is approximately 0.12 mm. When the gap is increased to the limit of 0.26mm, the valve guide and valve should be replaced. If the clearance is too small during assembly, valve jamming may occur.

When the diesel generator is dismantled the valve guide, the bottom of the cylinder head must be placed in the reverse direction, and it should be placed according to the position shown in Figure 2-10(b). Then the valve guide tube with wear exceeding the limit of 0.26 mm shall be dismantled with a special punch. under.

When assembling the valve guide, first place the bottom of the cylinder head down and lay flat as shown in Figure 2-10(a). Then use a special punch to press the new valve guide into the cylinder head and make the guide tube. The height of the high outlet valve spring seat is the same as the height before removal.

There are two methods for checking the clearance between the diesel generator valve stem and the valve guide tube:

1 experience test method: This inspection method is to swim a layer of oil on the valve stem, and then slowly push the valve stem into the catheter and reciprocate several times back and forth. When the cylinder head and the horizontal plane are at 45 degrees, the hand releases the valve head. If the valve slowly descends, it indicates that the clearance is appropriate. If the valve does not slide, the gap is too small and the inner diameter of the catheter should be reamed until the fit clearance meets the standard.

A special reamer can be used to ream the inside diameter of the catheter.

(3) valve seat ring

Valve seat trap is designed for reciprocating valves. It is used together with the valve to seal the combustion chamber. Its shape is shown in Figure 2-38. Valve seats are generally made of heat-resistant cast iron and pressed into the cylinder head. The position of the valve seat in the cylinder head is shown in Figure 2-10(b). The flying door cluster has long been subjected to the continuous impact of the valve and the Temple 2 measurement gap method of high-temperature and high-pressure gas. The inner diameter of the catheter and the outer diameter of the valve stem were measured with a vernier caliper, and the difference between them was compared with a prescribed standard value. If the gap is too large, the catheter or valve should be replaced: If the gap is too small, it is an eclipse and it is particularly prone to failure during use. In the long-term work, the cone of the valve seat ring will have pitting, pits, shortening of the seat ring, and widening of wear.

During the operation of the diesel generator diesel engine, the failure caused by the valve seat is mainly caused by the continuous impact of the valve, the ablation of the high-temperature gas and the incomplete combustion of the diesel in the combustion chamber, resulting in excessive carbon deposition.

1 observation method. The main observation is whether the tapered surface of the seat ring is widened due to wear, whether there is a leakage phenomenon when it comes in contact with the valve, whether it can meet the requirements, and whether there are pits, pits, and cracks on the cone surface.

2 measurement method. The depth of depression of the valve on the valve seat is mainly measured by a depth gauge, a vernier caliper, or a depth micrometer. If the depth of the recess is too large, the volume inside the combustion chamber will increase, the compression ratio will decrease, and the intake air volume will decrease, which will affect the output power of the diesel engine. The recess depth of the valve of a typical small high-speed diesel engine is within the range of 1.5-2.2mm.

If the concave depth, pits, and pits on the conical surface of the valve seat cone are not obvious and the amount of air leakage is small, the valve and valve seat grinding can be used to improve the sealing of the valve and the valve seat ring. Manual grinding method is shown in Figure 2-36.

If the valve seat group is seriously damaged and there is a large amount of air leakage, the new valve seat should normally be replaced. When replacing the new valve seat ring, remove the old valve seat ring with a special puller, then apply a small amount of oil on the new valve seat drawing, and use the special punch with the guide rod to press the new valve seat into the cylinder head Hole in the seat. The replaced valve seat must be reamed and ground before it can be used. The specific reaming method is as follows; after the new valve seat is pressed into the cylinder head seat hole, 45 is used first.

A (or 30 degree) reamer removes the valve seat due to the hardened layer on the surface. For small ordinary diesel engine valve seat working face, 45-degree reamer is generally used for reaming; for turbocharged diesel intake valve seat gardener, a 30-degree reamer for dumpling. Secondly, a reamer with 15 degrees or 75 degrees is used for correction based on the width of the contact ring after reaming and the position of the upper F. If the new valve seat is reamed and the width of the contact ring is more than 2.2mm and it is upside down, 15 can be selected. Reamer correction: If the width of the contact band is more than 2.2mm on the side and below it, a 75-degree reamer can be used for correction.

After reaming, the width of the contact ring should be in the range of 1.5-2.2mm, and then use a 45-degree (or 30-degree) knife to perform a precision hinge, and then let the new valve seat and valve to grind the dumped Until the seal requirement is reached.

The technical points in the dumpling cutting process are as follows: First, the guide rod of the reamer must not be allowed to move after inserting the valve guide tube; secondly, it should be smooth when rotating in a clockwise direction; and third, it should be ensured that the reamer is in the center line of the cylinder head with the horizontal plane of the cylinder head. Rotate at right angles.

(4) Diesel Generator Valve Spring

The shape of the valve spring is shown in Figure 2-39. The role of the valve spring is to ensure that the valve quickly falls on the valve seat ring and closes tightly, preventing the valve from being disengaged from the transmission mechanism due to the inertial force during opening and closing. The valve spring should have sufficient elastic force. The lack of spring force or spring breakage will affect the working conditions of the combustion chamber. For this reason, maintenance personnel should check the spring force when assembling the valve spring. When the free length of the old spring is less than about 4mm of the free length of the new spring of the same model, the new spring should be replaced.

When the valve has inner and outer springs, the spiral directions of the inner and outer springs should be opposite during the assembly process so as to prevent the single spring from breaking and affecting the other spring.

During the operation of the diesel engine, when the valve spring breaks or the spring force is insufficient, the interior of the valve cover generally sounds. The installation position of the valve spring is shown in Figure 240.

The valve transmission assembly is mainly composed of a tappet, a push rod, a sway assembly, a camshaft and a transmission mechanism. The role of the valve transmission assembly is to periodically open and close the intake and exhaust valves according to the working order of each cylinder of the diesel engine, so that the intake air in the combustion chamber Adequate, exhaust dry earned, and sealed well.

(1) Diesel generator set tappets and push rods

The role of the tappet and the report rod is to transmit the cam force to the rocker arm. The lattice arm overcomes the spring force of the valve spring to open the valve. When the thrust gradually decreases to the minimum, the spring force of the valve spring causes the valve to close. The physical appearance of the valve lifter and the push rod are shown in Figure 2-41 and Figure 242, respectively.

During the normal operation of the diesel engine, the tappet wear is generally small and the push rod does not bend. However, if the diesel engine is overloaded for a long time or if the load changes greatly during the operation (for example, the diesel engine used in the pile driver), it may easily cause serious scrape, serious wear and fatigue flaking of the tappet. When the above-mentioned damage occurs on the tappet, new parts should generally be replaced. If the valve is stuck or the valve falls into the cylinder during the operation of the diesel engine, and a car accident occurs, the bar will be evaluated. When the bending waste is too large, it should be straightened or replaced with new ones.

(2) Grid arm assembly

The physical appearance of the shaking stay assembly is shown in Figure 2-43. The total achievement of the grid arm is to use lever principle to convert the upward thrust of the report to the pressure of the valve. The grid arms are divided into an intake valve swing arm and an exhaust valve swing arm, which are mounted on both sides of the rocker seat through a rocker shaft on the rocker seat. There is a bronze or powder metallurgy in the center hole of the rocker arm at both ends of the bearing. The bearing bush fits with the rocker shaft and can rotate freely. The rocker seat is fixed to the cylinder head with a stud. The contact portion of the rocker arm with the push rod includes an adjustment screw and a lock nut. Turning the adjustment screw can adjust the valve clearance. After adjustment, use a lock nut to prevent the adjustment screw from loosening during operation.

In the process of long-term rotation of the diesel engine, the prone to failure is the wear of the rocker arm and the rocker arm bush.

When the wear gap between them exceeds 0.25mm, the rocker bushing is generally replaced. Under normal circumstances, their labor clearance is 0.06mm.

To be continued...