Removal and dismantling of the engine cylinder head are covered in the relevant articles.
After dismantling the cylinder head, all head parts must be washed and cleaned of carbon deposits. We prepare the parts for inspection.
Checking the cylinder head
The cylinder head height h must be 137 mm (Figure 1).
Using a straightedge and a feeler gauge, we check the flatness of the cylinder head mating surfaces (Figure 2). The maximum permissible flatness deviation is 0.05 mm. Grinding of the surfaces is not permitted.
We check the cylinder head (absence of cracks and through corrosion) using the appropriate tool (Figure 3).
We check the length of the head retaining bolts. The length of the bolts excluding the head must be no more than 117.7 mm.
If new bolts are fitted, they need not be lubricated before fitting; used bolts must be lubricated with engine oil. Subsequent re-tightening of the cylinder head retaining bolts is neither required nor permitted, otherwise the probability of bolt failure when undoing them increases sharply. Before tightening the bolts, remove dirt and oil remaining in the threaded holes of the cylinder block.
We measure the gasket thickness (Figure 4). The thickness is measured at the point indicated by the arrow in Figure 4. The thickness of a new gasket must be 0.96±0.06 mm; the thickness of a compressed gasket must be 0.90±0.02 mm.
We inspect the hydraulic tappets and rockers.
We measure the valves in accordance with Figure 6. The valve dimensions must correspond to the data in the table.
Main valve dimensions
| Description | Inlet valves | Exhaust valves |
|---|---|---|
| Stem diameter D1, mm | 5.470–5.485* | 5.456–5.471* |
| Head diameter D2, mm | 32.70±0.12 | 27.96±0.12 |
| Valve length L, mm | 109.32 | 107.64 |
| Working chamfer angle А | 45° 45′ | 45° |
| Minimum thickness of the cylindrical band of the valve head T, mm | 1.15 | 1.27 |
| Valve lift, mm | 9.221 | 8.075 |
* the valve stem diameter D1 is measured at a distance X1: inlet valves X1 = 75.14±0.35 mm; exhaust valves X1 = 77.5±0.35 mm.
Valve guide bushes
The inclination of the inlet valve guide bush is 63°30′ (Figure 7). The inclination of the exhaust valve guide bush is 66°. The height of the protruding part of the valve guide bush Н is 11±0.15 mm for both inlet and exhaust valves.
Oil-deflector caps
The oil-deflector caps are removed using the Mot1335 tool. The oil-deflector caps are fitted using the Mot1511 tool. Before fitting, the oil-deflector caps must not be lubricated. Fit the oil-deflector caps in accordance with the instructions in Figure 8.
- Insert the valve into the cylinder head.
- Place the tip of the Mot1511 tool onto the valve stem (the inner diameter of the tip must equal the stem diameter) (see Fig. 8).
- Press the valve against its seat.
- Fit the unlubricated oil-deflector cap onto the tip.
- Advance the oil-deflector cap by pushing it through the tip.
- Remove the tip.
- Fit the drift onto the oil-deflector cap. The inner diameter of the drift must coincide with the valve stem diameter. In addition, the lower part of the drift must bear partially against the oil-deflector cap over the surface that serves as a support for the valve spring washer.
- Carefully press the oil-deflector cap in by tapping with the palm on the upper part of the drift until the oil-deflector cap contacts the cylinder head (see E, Fig. 8).
- Repeat the above operations for all valves.
Checking the valve springs
With deformations B and C, operation of the spring is permissible if the deviation from the vertical is not more than 1.2 mm; with loss of shape (D) — the spring must be replaced. Even if the spring shape is preserved, its mechanical properties must be checked (height under a certain load). Only after such a check is the suitability of the spring for further service determined (see the table).
Valve spring parameters
| Parameter | Value, mm |
|---|---|
| Height in the free state | 41.30 |
| Spring height in the working state | 23.20 |
| Inner diameter | 18.80±0.20 |
| Outer diameter | 27±0.2 |
| Wire cross-section | Oval |
| Height / under load | 34.50 / 180–200 N; 24.50 / 563–617 N |
If a new spring is available, its characteristics can be compared with those of the old springs. Fit the new and the old springs one after the other, through washers, onto a long bolt. Tighten the bolt nut so that the height of the new spring decreases by 10 mm. Measure the height of the old spring. If the height of the old spring has decreased from 9 to 11 mm (±10 %), it can still serve; if more — replace the old spring.
Checking the valve clearance in the guide bush
The clearance between the stem and the valve guide bush can be checked in two ways.
First method
Raise the valve head by 25 mm, then measure with a dial gauge the displacement of the valve in the direction of the arrows (see Fig. 10) at 90° to the camshaft axis. Half of the value obtained gives the clearance between the stem and the valve guide bush.
Second method
Measure the valve stem diameter and the inner diameter of the guide bush (see Fig. 11).
Nominal clearance, mm:
- inlet valves: 0.015—0.048;
- exhaust valves: 0.029—0.062.
Checking the camshafts
The cam height Н (see Fig. 12) of the camshafts must correspond to the data in the table.
Camshaft dimensions
| Parameter | Value, mm |
|---|---|
| Camshaft axial clearance (inlet and exhaust valves) | 0.080–0.178 |
| Diametral clearance in the bearings | 0.040–0.082 |
| Number of bearings | 6 |
| Camshaft journal diameter: journals No. 1 | 24.979–25.000 |
| Camshaft journal diameter: journals No. 2, 3, 4, 5 | 24.979–25.000 |
| Camshaft journal diameter: journal No. 6 | 27.979–28.061 |
| Cam height Н: inlet valves | 40.661±0.030 |
| Cam height Н: exhaust valves | 40.038±0.030 |
Otherwise — replace the camshaft or carry out a restoration repair.
Check the clearance of the camshaft journals in the cylinder head bearings; to do this:
- Fit the cylinder head cover in place and tighten its retaining bolts to the specified torque.
- Using a bore gauge, measure the diameters of all holes in the camshaft bearings (see Fig. 13); record the measurement results.
Note. The measurements must be taken in the vertical plane of maximum wear.
- Using a micrometer, measure the diameters of the camshaft support journals (see Fig. 14). The measurements must be taken on each journal in two mutually perpendicular planes. Take the smallest value on the journal as the base value.
- Compare the measurement results with the maximum permissible values.
- Then calculate the clearances on all journals and compare the obtained values with the maximum permissible values.
Based on the results:
- replace the camshaft, the cylinder head, or both.
Note. In case of wear of the camshaft and the cylinder head, a restoration repair is possible (spraying followed by machining). Often the price of such a repair is considerably lower than buying new parts.
- If the previous checks have not shown the need to replace parts, check the camshaft axial clearance as described below and, if necessary, replace the worn parts.
If the parts are new, carry out the check anyway; it is not difficult, but it is important for confidence in the results of the repair performed.
- Fit the camshafts, ensuring their correct position.
- Fit the cylinder head cover.
- Tighten in the sequence shown in Fig. 15 to the required torque:
- cylinder head retaining bolts 13, 20, 22, 23: 8 N·m;
- cylinder head cover retaining bolts 1 to 12, 14 to 19 and 21 to 24: 12 N·m.
- Slacken the cover bolts 13, 20, 22, 23.
- Tighten in the indicated sequence the cylinder head cover retaining bolts 13, 20, 22, 23 to a torque of 12 N·m.
Secure the magnetic stand of the Mot588 axial clearance checking tool on the cylinder head, using for this purpose the mounting plate (3) of the Mot588 tool; tighten it with the oil separator retaining bolts (1) and spacer bushes (2) having the following dimensions:
- outer diameter: 18 mm;
- bolt hole diameter: 9 mm;
- height: 15 mm.
- Check the camshaft axial clearance, which must be within 0.080—0.178 mm.
- Remove the cylinder head cover and the camshafts.
