timing

The oil pump sprocket is attached via gear drive to a balance shaft. If it isn't timed properly, you'll get an engine vibration.

Thanks a lot for the answer.Harstat

So if it happens to be a few teeth off and you have an engine vibration, any harm done to the engine? (speaking hypothetically here)

Probably not, but it'll be very annoying when you drive the car. By the same token, the vibration will be felt in the entire car. I'd suppose that some items attached to the engine could experience vibration fatigue.