BMW 5251 Service Manual page 236

11
6-60
Cylinder Head and Valvetrain
Valve springs
The valve springs should be checked for fatigue. To quickly
check the springs, line them up in a row. Place astraight edge
across the top of the springs. Any spring that is significantly
shorter than the others is worn and should be replaced.
Valve spring specifications and wear limits are not available
from BMW.