Minimum allowable cylinder head height, not less than, mm:
- engines YP, YZ: 132.55;
- engines EP, OT, OS, OZ: 132.60.
Warping of the mating surface of the head with the cylinder block, not more than, mm: 0.1.
The diameter of the holes of the supports for the camshaft bearings, mm: 26.00-26.02.
Diameter of nests of pushers, mm: 35.00-35.02.
Valve seats
The valve seats are made from powder metallurgy steel and are non-replaceable. If signs of burning or wear are found that cannot be removed by grinding, replace the cylinder head.
Inlet valve specifications
Exhaust valve seat specifications
Valve guides
Valve guides made of special brass (engines YP, YZ) or bronze (engines EP, DT, OS, DZ) and pressed into the cylinder head. Guide bushings supplied as spare parts have a support shoulder.
Pressing force of guide bushings, not more than, tf: 1
Maximum allowable limit clearance (when worn) between valve stem and guide bush (measurement procedure is described on page 67), mm:
- for inlet valves: 1.0;
- for exhaust valves: 1.3.
Hole diameter in valve guide bushings, mm: 8.013-8.035.
Valves
Steel valves are located in the cylinder head in a row and are actuated directly by the camshaft cams through pushers or hydraulic pushers (DT, DS, DZ engines from July 1985). Exhaust valves are not subject to grinding, only their grinding to the seats is allowed.
Inlet valve specifications
*91.00 mm from July 1985 for DT, DS, DZ engines.
Exhaust valve specifications
*90.80 mm from July 1985 for DT, DS, DZ engines.
Clearances in the valve drive mechanism
Engines of all models
The gap between the camshaft cams and shims at a coolant temperature above 35°C should be 0.25±0.05 mm for intake valves and 0.45±0.05 for exhaust valves, on a cold engine, respectively 0.20±0.05 and 0.40±0.05 mm.
The gap is adjusted by selecting the thickness of the shims mounted on the upper ends of the pushers. Spare parts are supplied with shims with a thickness of 3.00 to 4.25 mm at intervals of every 0.05 mm. The thickness of the washer is marked on its bottom surface. The washer is installed with the marked surface down.
DT, DS, DZ engines since July 1985
The gaps in the valve drive mechanism are compensated automatically by hydraulic tappets.
Valve springs
Each intake and exhaust valve has two springs. The intake and exhaust valve springs are the same.
Calibration characteristics of valve springs
Pushers
The valve lifters are located directly in the cylinder head. Adjusting washers of various thicknesses are installed on the upper ends of the pushers to adjust the thermal clearances of the valves. Since July 1985, DT, DS and DZ engines have been equipped with hydraulic tappets to compensate for thermal valve clearances.
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