Just bought a Stihl 110 4 mix power head with edger attachment. They assembled it for me but did not demo it. The engine starts (sounds wicked) but the edger won't spin. I took it apart and tried to put it right but I can't get that line and arrow completely flush. There seems to be half a cementer away and I just can't get it in. also, is it true you only let the edger dig about 5mm of depth? I just read that in the manual, I thought it was inches.