Sounds like your putting a 9 speed front derailleur on an 8 speed crank. The normal jump for the 9 speed is from 32 to 44 or 12 teeth. Is the 8 speed crank a 32/42 jump. The 9 speed derailleur can be made to work on the smaller 42 ring but it will have to be spaced farther away from the 42 ring for the back of the cage to clear the middle ring.