Valve seats, reworking
WARNING: This page is about a different car, the 2006 Audi A8, 2005 Audi A8, and 2004 Audi A8. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
- If a perfect contact pattern is not achieved by grinding the valve seats, rework the valve seats.
Special tools, testers and auxiliary items required
- Depth gauge
- Valve seat refacing tool
NOTE:
- When repairing engines with leaking valves, it is not sufficient to rework or replace valve seats and valves. It is particularly important to check valve guides for wear on engines with higher mileage performance → Valve guides, checking .
- Only reface valve seats enough until a perfect contact pattern is obtained.
- Before refacing, determine maximum refacing dimension.
- If the reworking dimension is exceeded, the function of the hydraulic lifters can no longer be guaranteed and therefore the cylinder head should be replaced.
Determining maximum allowable refacing dimension
- Insert valve and press it firmly against the valve seat.
NOTE:
- If the valve is to be replaced as part of a repair, use a new valve for the calculation.
Fig 1: Measuring Distance Between End Of Valve Stem And Camshaft Center Axle (Camshaft Center Axle Is Located At The Level Of Cylinder Head Upper Edge)
- Measure distance - a - between end of valve stem and camshaft center axle (camshaft center axle is located at the level of cylinder head upper edge).
- Determine maximum allowable refacing dimension using distance measured and minimum dimension.
| Minimum dimensions | ||
|---|---|---|
| Outer intake valves | Center intake valves | Exhaust valves |
| 39.3 mm | 41.0 mm | 40.6 mm |
Measured distance minus minimum dimension = maximum permissible refaced dimension.
| Example for outer intake valve: | |||
|---|---|---|---|
| Measured distance | 39.7 mm | ||
| - | Minimum dimension | 39.3 mm | |
| = | Maximum permissible refacing dimension | 0.4 mm | |
NOTE:
- If the maximum permissible refacing dimension is 0 mm or less, repeat measurement using new valve. If measurement result is still 0 mm or less than 0 mm, replace cylinder head.
Valve seats, reworking
| Intake valve seat | ||
|---|---|---|
| a | = | Dia. 26.6 mm |
| b | = | Approx. 1.0 mm |
| Z | = | Cylinder head lower edge |
| α | = | 45° valve seat angle |
| β | = | 30° upper correction angle |
| g | = | 60° lower correction angle |
| Exhaust valve seat | ||
|---|---|---|
| a | = | Dia. 26.0 mm |
| b | = | Approx. 1.0 mm |
| Z | = | Cylinder head lower edge |
| α | = | 45° valve seat angle |
| β | = | 30° upper correction angle |
| g | = | 60° lower correction angle |