Inspection and Maintenance Of Cylinder Head And Block

Inspection and maintenance of cylinder cead and block

1) Inspection of cylinder block

Cylinder block water jacket crack detection with water pressure method: seal the outlet of the cylinder block water jacket, press water into the water jacket with a hydraulic press at a pressure of 343~441kPa, keep it for 5 minutes, check all parts of the exterior, if there is water seepage, it means that there are cracks there.

①Cylinder block upper and lower flatness deviation detection Place the steam body on the flat plate, use a knife edge ruler or optical axis longer than the length of the steam body, and place it on the plane of the cylinder body, and use a thickness gauge to detect the light leakage. It is required that the flatness deviation of the cylinder block plane within the range of every 50mmX50mm is not more than 0.05mm. On the entire length plane, the limit deviation of the cast iron and aluminum alloy cylinder blocks with a cylinder block length less than 600mm is 0.15mm, and the cylinder block length is greater than 600mm. The limit deviation of the cylinder block is 0.25mm, and the limit deviation of the aluminum alloy cylinder block is 0.35mm. When the limit is exceeded, it should be ground.

② Testing the coaxiality of crankshaft bearing holes Use a comprehensive gauge with the same size as the bearing hole to detect the coaxiality error of crankshaft bearing holes and camshaft bearing holes. If the coaxiality error is within the range specified by the standard, the measuring rod can pass through the bearing hole, otherwise the measuring rod cannot pass through. Usually, the long rod is used to detect all crankshafts on the entire cylinder block; the short rod is used to detect the coaxiality error of two adjacent bearing holes.

③ The rear end of the cylinder block faces the positioning sleeve and the mandrel for the detection of the verticality error of the crankshaft bearing hole axis (the mandrel must be positioned axially), and the dial indicator is fixed on the mandrel, so that the guide rod of the watch frame The axis of the mandrel is vertical. When the mandrel is rotated, the dial indicator moves along the guide rod, and the maximum full runout of the end face is measured as the measured error.

④Check the parallelism error between the crankshaft bearing axis and the camshaft bearing axis Install a centering sleeve in the crankshaft bearing hole and the cam oil bearing hole, insert the measuring mandrel into the sleeve, and measure the distance between the two axes at both ends of the mandrel with a micrometer The difference should not be greater than 0.10mm.

2) Repair of the upper plane of the cylinder block

When the flatness of the upper plane of the cylinder block exceeds the limit, it should be repaired. The repair method is milling or grinding. In order to ensure that the cylinder axis and the crankshaft axis are perpendicular to each other after milling and grinding, the positioning datum must be selected. Generally, the joint surface of the front and rear bearing holes of the blood body spindle and the bearing cover is the benchmark. In order not to affect the compression ratio due to the reduction of the cylinder stroke after the plane milling of the cylinder block, the milling amount should be controlled within 0.24~0.25mm. Zhengguang's Pavilion

Repair of cylinder head

Common damage to the cylinder head includes warping, ablation, cracks, etc.

1) Detection and correction of the flatness of the cylinder head

The deformation of the cylinder head plane is due to improper tempering during the casting process, uneven torque of the tightening bolts during installation or removal during repair (especially hot cars) - caused by improper placement

①Measurement method Put the knife edge ruler on the plane of the cylinder head, and use the thickness gauge to test at the gap. Within the range of 50mmX50mm, the flatness error of the lower plane of the cylinder head of the side valve engine should not be greater than 0.05mm.

②Calibration method Put the deformed protrusion of the cylinder head on the flat plate, cushion the undersides with 0.5~0.7mm thick gaskets, and then gradually pressurize the convex surface with a press or screw, and at the same time use a blowtorch to the deformation. Heating to 300~4000, when the cylinder head plane is attached to the flat plate, keep it cool, and remove it for re-testing. If there is local deformation, use the scraping method to correct it.

2) Measurement and adjustment of combustion chamber volume

After the cylinder head plane is ground, the volume of the combustion chamber will become smaller, and local corrosion will also affect the change of the combustion chamber volume. When the combustion chamber volume exceeds the original specification, it will affect the Stability at idle speed must therefore be measured and adjusted.

①Measurement method The measurement of the volume of the combustion chamber of the cylinder head should be carried out after thoroughly removing the oil stains, carbon deposits and glue in the combustion chamber, and the cylinder head should be in a horizontal position. Generally, water or mixed liquid (80% kerosene and 20% engine oil) is used as the measuring liquid. When measuring, inject the object with the determined volume, and reflect the size of the volume through the pressure gauge.

②The correction method is small and the volume is small: a layer of metal can be milled off at the bottom of the combustion chamber, or a layer of the surface can be etched off by the electro-erosion method. The volume is too large: a layer of metal can be welded on the side wall of the combustion chamber.

3) Precautions when disassembling and assembling the cylinder head bolts

Disassembling and assembling the cylinder head bolts using the correct operation process is an effective measure to prevent the deformation of the cylinder head and the damage to the cylinder head gasket. When disassembling and assembling the cylinder head bolts, it should be carried out in the order specified by the original factory. If there is no original regulation, the dismantling bolts should be loosened from both ends to the middle in steps: when assembling, they should be tightened sequentially from the middle to both ends, preferably three times. The first time is to tighten it by hand, and the second time is to tighten and disassemble the cylinder head at one-third of the specified torque, which should be done after the engine has cooled down. The tightening torque of the cylinder head bolts shall be tightened according to the original standard.

(3) Repair process of cylinder

1) Cylinder measurement

The purpose of cylinder measurement: mainly by measuring the wear degree of the cylinder, and determining the technical state of the engine according to the wear amount of the cylinder. If the wear of the cylinder exceeds the limit of use, the cylinder liner should be replaced or the cylinder should be repaired by boring and grinding.

The wear of the cylinder is usually measured with an inner diameter gauge (also called a cylinder gauge)。

① Install the dial indicator in the upper end hole of the watch rod. When the needle swings slightly, you can fasten the dial indicator with the locking nut. Generally, the surface and the movable measuring rod are in the same direction.

②According to the measured cylinder diameter, select the appropriate length of the post, screw on the fixing nut, and install the post into the post seat at the lower end of the gauge rod of the measuring cylinder.

③ Insert the measuring rod of the cylinder gauge into the upper part of the cylinder, adjust the length of the connecting rod, it is appropriate when the needle rotates 1~1.5 circles, and then tighten the fixing nut on the connecting rod.

④According to the wear law of the cylinder, find out the maximum wear of the cylinder within the stroke of the piston ring, and turn the dial to align the "0" position with the pointer.

When measuring, the measuring cylinder should be swung back and forth so that the measuring rod is perpendicular to the axis of the cylinder, so that the measurement can be accurate (when the measuring cylinder is swung back and forth and the needles indicate a certain minimum value, it means that the measuring rod is perpendicular to the cylinder axis). cover

⑤ Move the cylinder gauge up to the shoulder of the cylinder or find a minimum diameter in the cylinder. At this time, the difference between the position pointed by the dial and the "O" position on the gauge is the wear amount of the cylinder.

⑥ Take out the cylinder gauge, and use an outer micrometer to measure the length of the measuring rod of the cylinder gauge at the maximum diameter in the cylinder, which is the maximum diameter of the cylinder after wear.

2) The service limit of cylinder bore wear

If the cylinder bore wear exceeds the service limit, the cylinder liner should be replaced or the cylinder should be repaired by boring and grinding.

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