- pressure drop in the engine lubrication system. The cause of this malfunction is often increased wear on the camshaft journals and sockets in the camshaft bearing housings. When the nests are worn out, the head of the block assembly is replaced, since the nests are processed together with the bearing housing installed on the head;
- valve knock with serviceable hydraulic pushers (see «Checking and replacing hydraulic pushers») in the valve mechanism. It can be 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 those required directly for replacing them (tools are used only for preparatory operations), as well as a micrometer and inside gauge.
1. Remove the camshafts from the engine (see «Replacement of valve stem seals»).
2. Inspect the camshafts. On the working surfaces of the necks 2, scoring, nicks, scratches, aluminum enveloping from the bearing seats in the housings and the head of the block are not allowed. On the working surfaces of the cams 1, scuffing and wear of more than 0.5 mm, as well as wear of the cams in the form of a cut, are not allowed. Replace the shaft with detected defects.
3. In workshops equipped with special fixtures and tools, you can check the radial runout of the camshaft journals (it should not exceed 0.02 mm).
4. Measure the diameters of the bearing journals of the shaft. They should be 23.915–23.931 mm.
5. Inspect the bearing housing..
6.... and camshaft bearings in the block head. Cracks in the hull are not allowed. On the working surfaces of the bearings under the necks, risks, scratches, scuffs, excessive wear are not allowed.
7. Install the camshaft bearing housing on the block head and tighten its fastening bolts to the recommended torque (see annex 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 the bearings by 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, after replacing the shafts, the clearances exceed the maximum allowable value, replace the cylinder head assembly with the camshaft bearing housing.
9. Establish camshafts and all removed details in an order, the return to removal.
Note. Apply a sealant to the surface of the cylinder head mating with the camshaft bearing housing «Loctite-574» in the form of a roller with a diameter of 2 mm.