valve seats (see fig. 3.5) are made of austenitic powder metallurgy steel and cannot be replaced. If there are signs of burning or wear that cannot be removed by grinding, the entire cylinder head is replaced.
Table 5.3. Characteristics of valve seats
Parameters | Valve seat | |
inlet | prom | |
Model engine « N62 B44» | ||
Valve seat diameter, mm | ||
- nominal | 34,5 | 28,4 |
- admission | from 0.00 to +0.1 | |
Working chamfer angle, degrees | 45 | |
Correction angle, outer | 15 | 15 |
Correction angle, internal | 60 | 60 |
Working chamfer width, mm | 1,25 ± 0,25 | 1,65 ± 0,25 |
In this case, it is necessary to maintain the maximum allowable size. If this size is exceeded, then the reliability of gap compensation during the operation of hydraulic lifters is violated. The valve seat is lapped (being repaired) until a reliable contact patch is obtained. The valve seats have an additional narrowing - the angle of external correction. During processing, the external correction angle must be kept at 15°.
Technology for lapping valve seats and checking valve guides (see fig. 3.7) identical for all engines.
Maximum allowable clearance (during operation), between valve stem (diameter 6.0 mm) and the guide sleeve should be no more than 0.5 mm.
Attention! Valve guides are not available as spare parts.