Question

when measuring a valve guide with a ball gauge, you should
a) allow the gauge to expand until it presses hard against the bore walls
b) never move the gauge once it is inserted
c) rock the gauge from side to side to center it in the bore
d) loosen the adjuster nut before retracting the gauge from the bore

Explanation:

When using a ball - gauge to measure a valve guide, rocking the gauge from side to side helps center it in the bore for an accurate measurement. Allowing the gauge to press hard against the bore walls can give inaccurate readings and may damage the gauge or bore. Not moving the gauge once inserted may not ensure it is properly positioned. Loosening the adjuster nut before retracting is not a standard step in the measurement process.

Answer:

C. rock the gauge from side to side to center it in the bore