I bought a koken 1/2" drive impact socket to get mine undone, about $20 or so, they only had 10mm in impact so that's what I got. Worked a treat too, except clearance is a tad tight especially where the hex parts on the camshafts are. My bolts were very tight- I had a 3/8" drive in hex set but I just got the 'somethings gonna give and it's not the bolt' feeling so go the koken socket. I like Koken tools but they are a bit dear so I don't have many.