Disassembly order:
- remove the cylinder head and install it on a workbench with a wooden cover;
- remove the fuel injectors;
Pic. 3.29. Compressing the valve spring and extracting crackers
- using a special device, compress each valve spring and, having moved a sufficient distance down the valve stem, the upper spring plate, remove the crackers (pic. 3.29). If crackers «stuck», gently tap the end face of the valve with a copper-faced hammer;
Pic. 3.30. Removing the top plate and valve spring
Pic. 3.32. Valve installation kit in bag
Pic. 3.31. Removing the valve from the guide sleeve
- remove the top plate, spring and remove the valve from the guide sleeve (pic. 3.30, 3.31). Put the set of parts in a separate plastic bag, marking the place of their installation (pic. 3.32);
Pic. 3.33. Removing the oil seal
- remove the valve stem seals, which simultaneously serve as the lower plates of the springs, from all guide bushings (pic. 3.33).
Parts Inspection
Thoroughly clean the removed parts from dirt and carbon deposits. Remove the remains of the old gasket on the mating surface of the cylinder head only by chemical means (see subsection «Removal and installation of a head of the block of cylinders»). To remove carbon deposits from the combustion chambers, use only aluminum scrapers. Rinse the block head thoroughly with kerosene or white spirit. Use a wire brush in the drill chuck to remove carbon deposits from the valves.
When inspecting and measuring parts, consider the technical data given in Table. 3.2.
Carefully inspect the cylinder head for cracks. If cracks are found, the head must be replaced.
Check if the flatness of the mating surface of the head is broken using a metal ruler, applying it along, across and diagonally and measuring the gap with a feeler gauge. Permissible gap in all dimensions is not more than 0.05 mm. If the gap exceeds 0.05 mm, the head must be replaced.
Inspect the valve faces for pitting and burns, paying particular attention to the exhaust valves. If significant damage is found on the working chamfers, replace the valve. Minor surface defects are eliminated by lapping the valve.
Lapping of the valve is performed as follows. Apply a small amount of coarse abrasive paste to the contact surface of the valve or seat and insert the valve into the valve guide. Place the valve lapping tool with suction cup on the valve head and lap the valve in a semi-rotary motion. Change the position of the valve relative to the seat from time to time and continue lapping until the seat and valve surfaces are a uniform gray color. Then repeat lapping with a fine paste. When finished lapping, remove any remaining lapping paste, being careful not to let the lapping paste get into the guide bushing. Wipe the valve and seat with a rag soaked in kerosene and then with a dry cloth.
Make sure, by rotating the valve, that there is no bend in its stem. The end face of the valve must be free of chips and signs of wear. Replace damaged valves.
Measure the diameter of the valve stem with a micrometer and compare the measurement results with the data in Table. 3.2.
Also measure the inner diameter of the corresponding guide bush. Calculate the gap and compare the result with the data in the mentioned table. If the clearance is out of specification, replace the guide bush or valve. It is better to entrust the replacement of bushings to specialists. For self-repair, use a mandrel with shoulders and knock out the guide bushing towards the combustion chamber. Place the new bushing in the freezer for one hour before installation, then press it into the head with a mandrel from the side of the camshaft to the prescribed protrusion height above the surface. Expand the inner diameter of the guide bush to the required size.
Check valve seats. In the presence of significant surface damage, the chamfers of the saddle are subject to grinding on a special machine. Minor surface imperfections can be removed by lapping as described above. If it is necessary to grind the valve seats, it is necessary to specify the maximum possible depth of grinding, since if the metal is removed excessively, the correct operation of the valve lifter is not ensured. The solution of this issue should be entrusted to specialists.
Inspect the valve springs for broken or cracked coils. The dimensions of the springs must correspond to the data given in table. 3.2. The geometry of the spring must not be changed. Replace damaged springs.
Table 3.2. Technical data for cylinder head, valve train parts and camshafts
Inspect hydraulic tappets for wear and cracks. Minor abrasions on the working surface are allowed.
All valve stem seals must be replaced without fail.
Pic. 3.34. Measurement of axial clearance of the camshaft
Check the axial clearance of the camshafts using an indicator (pic. 3.34) and compare the result with the table.
Check the camshafts. The surface of the necks and cams should be smooth with a matte finish.
The bluish color of the surfaces indicates overheating of the engine or its insufficient lubrication, and scuffing, chipping, bright shine indicate wear. Accelerated wear begins immediately after damage to the outer layer of the camshaft, so damaged parts should always be replaced.
On a special stand, check the camshafts for radial runout. Its maximum allowable value is not specified by the manufacturer, but a value of 0.1 mm can be used as a guide. If the measurement result exceeds this value, then the issue of replacing the camshaft should be decided.
Assembly order:
- lubricate the valve stems with engine oil and insert them into the guide bushings of the cylinder head;
- put on the valve stem the installation tip supplied with the valve stem seals. Do not lubricate oil seals before installation;
- while holding the valve pressed against the seat, carefully put the valve stem seal on the tip without distortion;
- push the cap along the shaft to the guide sleeve and remove the tip;
- make sure that the cap is installed without distortion, and install a pusher to press it in;
- tapping the upper part of the pusher with your palm, move the cap until it comes into contact with the cylinder head;
- install the spring and the upper spring plate;
- using the tool, compress the spring and install crackers in the groove on the valve stem. To facilitate assembly, lightly grease the crackers with grease;
- assemble the remaining valve assemblies in the same way;
- through a wooden spacer, tap lightly on the protruding ends of the valves for the correct fit of the parts;
- install fuel injectors.