Figure 2.25. Valve seat angles and lapping
8-valve engines
Normal value: inlet valve - 41.45 mm, outlet valve - 41.35 mm.
Limit value: inlet valve - 41.95 mm, outlet valve - 41.85 mm.
12-valve engines
Normal value: inlet valve - 43.70 mm, outlet valve - 43.30 mm.
Limit value: inlet valve - 44.20 mm, outlet valve - 43.80 mm.
Replacing the valve seat ring
1. Before removing the valve seat ring, first use a milling cutter to rough up the inside of the ring to make it easier to remove. Then replace the ring with a new one.
2. Drill the hole for the valve seat in the cylinder head according to the outer diameter of the valve seat ring, taking into account the permissible repair dimensions.
12-valve engines
Inlet valve (primary):
- Boring by 0.30 mm: 27.421-27.441 mm.
- Boring by 0.60 mm: 27.721-27.741 mm.
Inlet valve (secondary):
- Boring by 0.30 mm: 32.425-32.445 mm.
- Boring by 0.60 mm: 32.725-32.725 mm.
(The material was borrowed from the website MitsubishiMan)
Exhaust valve:
- Boring by 0.30 mm: 35.425-35.445 mm.
- Boring by 0.60 mm: 35.725-35.745 mm.
8-valve engines
Inlet valve:
- Boring by 0.30 mm: 36.300-36.325 mm.
- Boring by 0.60 mm: 36.600-36.625 mm.
Exhaust valve:
- Boring by 0.30 mm: 32.300-32.325 mm.
- Boring by 0.60 mm: 32.600-32.625 mm.
3. Before installing the valve seat ring, heat the cylinder head to 250° or cool the ring to avoid deformation of the cylinder head bore.
4. Lapping the valve seat. The angles and lapping of the valve seat are shown in Figure 2.25.