im wondering if thats an anti tampering shear bolt, designed so that the head snaps off at a given torque setting to discourage anyone from altering the timing and thus doing any tuning. the pic does look like a shear bolt. this does make sense if it was an american market model, does it have the daft emissions controls on the air inlet side too? to get them off, you need to put an m6 or m8 nut on top of the bit shown in the pic, and then with a mig welder, weld the nut onto the head of the bolt, and remove it with an ordinary socket set. dont do it whilst its red hot, but do it before it cools completely. the thermal shock of the welding often assists in removing these. many jap bikes used similar bolts to secure their ignition locks to discourage hotwiring!
