Help!!,I need a piston for 031 AV,I got one on E-bay (new) (Golf brand) when I put it on with cylinder off and turned crank it hits and wont go 360 degrees around, put old on and no problem, sent it back after calling vendor ( who says he's sold hundreds and never had a problem ),he says it looks the same as rest of one he has !! I NEED A PISTON HELP thanks Duke