1. Check valve disc (pic. 2.22). The contact surface of the valve seat must be in the middle of the valve disc and extend evenly over the entire surface.
Pic. 2.22. Checking the valve disc
2. If the valve head height is less than acceptable, replace the valve.
Normal value: intake valve - 1.0 mm, exhaust valve - 1.5 mm.
Limit value: intake valve - 0.5 mm, exhaust valve - 1.0 mm.