They aren't magnetic, also if you put the cylinder on top dead center, that doesn't always
mean that the whole rotating assembly won't move on you if you put too much air
pressure into that cylinder. The fix to that would be to put a rachet on the crank pulley
and wedge it so it wont move. Because that's what happened to me and a buddy, we
had air into the cylinder and the piston was at tdc and the whole assembly rotated and
moved so it fell into the cylinder, so then we pulled the head....
Chris.