- pressure drop in the engine lubrication system. The cause of this malfunction is often increased wear of the camshaft journals and seats in the camshaft bearing housings. When the sockets are worn out, the cylinder head assembly is replaced, since the sockets are processed together with the bearing housing installed on the head;
- valve knocking with serviceable hydraulic tappets (see "Checking and replacing hydraulic tappets") in the valve mechanism. It is caused by increased wear of the camshaft cams due to the use of low-quality engine oil or damage to the oil filter.
You will need: the same tools as for replacing valve stem seals, except for those required for replacing them (tools are used only for preparatory operations), as well as a micrometer and bore gauge.
1. Remove the camshafts from the engine (see "Replacing the valve stem seals").
2. Inspect the camshafts. On the working surfaces of journals 2, no burrs, nicks, scratches, or aluminum drag from the bearing seats in the housings and block head are allowed. On the working surfaces of cams 1, scoring and wear exceeding 0.5 mm, as well as wear of cams in the form of faceting, are not allowed. Replace the shaft with any detected defects.
3. In workshops equipped with special devices and tools, it is possible to check the radial runout of the camshaft journals (it should not exceed 0.02 mm).
4. Measure the diameters of the shaft bearing journals. They should be 23.915–23.931 mm.
5. Inspect the bearing housing…
6. …and the camshaft supports in the cylinder head. Cracks on the body are not allowed. No marks, scratches, burrs or excessive wear are allowed on the working surfaces of the journal supports.
7. Install the camshaft bearing housing onto the cylinder head and tighten its mounting bolts to the recommended torque (see appendix 1). Measure the inside diameters of the camshaft housing bearings. They should be 24.000–24.025 mm.
8. Calculate the gaps between the shaft journals and supports based on the difference in size. For new parts, the gaps should be 0.069–0.11 mm. If after operation the gaps exceed 0.2 mm, replace the camshafts. If, even after replacing the shafts, the clearances exceed the maximum permissible value, replace the cylinder head assembly with the camshaft bearing housing.
9. Install the camshafts and all removed parts in the reverse order of removal.
Note: Apply a 2 mm bead of Loctite 574 type sealant to the cylinder head surface mating with the camshaft bearing housing.