Cylinder head and valves — cleaning and checking (Opel Astra G)

1. Thorough cleaning of the cylinder head and valve mechanism parts followed by inspection will allow us to assess the scope of work required to repair the valve mechanism.

Note: If the engine has been overheating frequently, the cylinder head may have become warped, carefully check for signs of head deformation.

Cleaning

2. Clean the cylinder head sealing surfaces.

3. Clean the combustion chambers, all holes and channels from carbon deposits, then wash the cylinder head with solvent.

(Text copied from an online resource: OpelBook.ru)

4. Remove heavy carbon deposits from valves.

Examination

Note: Before concluding that parts need to be reground, be sure to complete all of the inspection procedures described below.

Cylinder head

5. Carefully inspect the head for cracks, signs of coolant penetration, and other damage. If cracks are found, replace the cylinder head.

6. Check the deformation of the cylinder head split plane (see photo)If the split plane is found to be warped, the head should be replaced (not subject to polishing).



7. Check the condition of the valve seats. In the presence of pitting (pits), cracks, traces of burnout, you will need to repair the head in the workshop of a car service station. Minor defects can be removed by lapping the valve.



8. Check the wear of the guide bushings (wear of bushings is one of the reasons for the appearance of bluish smoke from the exhaust pipe).. To do this, insert the valve into the corresponding guide bushing and rock it from side to side. A small, barely noticeable play is acceptable. If the valve play in the bushing is significant, measure the valve diameter. If the valve diameter has noticeably decreased due to wear, replace the valve. If the valve stem diameter is normal, replace the guide bushing (performed in a car service workshop). It is also recommended to check the clearance between the bushing and the valve, by the difference between the measured inner diameter of the bushing and the diameter of the valve. New bushings are pressed in after they have been deeply cooled. The amount of bushing protrusion above the cylinder head is specified in the Technical Data.

9. If the guide bushings are to be changed, the valve seats should be reground (or to over-center) only after pressing in new bushings.

Valves

10. Check the valves for cracks, burn marks, scoring and a bead formed due to wear on the rods. Check the bend. Roll the valves on a smooth hard surface. Check the wear on the end of the rod. If any signs of wear or damage are found, replace the valve.

11. If this check reveals that the valve is in satisfactory condition, then measure the valve diameter in several places (see photo). A noticeable difference in diameter indicates wear of the valve stem. If a noticeable difference in diameter is found in at least two places, replace the valve.





12. If the valves are in satisfactory condition, they should be ground to the seats. If the seats have only minor damage, or the seat has been reground, then lapping can be done with a fine-grained compound. A coarse-grained lapping compound should only be used if traces of deep wear or severe burnout of the seats are detected. In this case, the cylinder head and valves should be checked by an experienced specialist to determine whether the seats should be re-countersunk or replaced.

13. Before lapping, place the cylinder head on a flat surface with the combustion chambers facing up.

14. Apply a thin layer of lapping paste to the seat chamfer. Perform lapping by turning the device 180° in both directions and periodically lifting the valve to evenly redistribute the abrasive material (see photo).



15. Lapping on a coarse compound ends after the formation of a monotonous matte belt on the chamfers of the valve and seat (see photo). Wipe the valve and seat from the remaining paste and continue grinding with a fine-grained compound. Grinding is considered complete when a uniform, solid, grayish belt forms on the valve and seat chamfers. Further grinding is not allowed, since excessive wear of the seat may make subsequent repairs impossible.





16. After finishing grinding all valves, thoroughly wash all parts with solvent.

Valve Mechanism Parts

17. Check the springs for signs of chipping and damage. A rough check of the spring condition can be made by comparing the removed spring with a new one.

18. Check the spring deviation from the vertical using a square and compare with the standard

19. On single-shaft 1.6L engines, bearings are built into the support washers of the exhaust valve springs, ensuring the valve rotation and protecting the seat from carbon deposits. If the bearing is jammed or damaged, replace the support washer.

20. If at least one of the springs is damaged, has an increased deviation from the vertical, or has lost elasticity, then replace all the springs in the set. Keep in mind that during major repairs, it is recommended to change the valve springs regardless of their condition. The valve stem seals are changed regardless of their condition.