Just bought myself a galaxy off ebay with a bit of a missfire...... Guy recons it could be the head gasket, but where can i find the timing chain timing marks etc, and how long approx would it take a average DIYer to do? He's not serviced it for some time, changed the plugs on his front to see if that made a difference, as a get me home repair but you should've seen the state of the one ones that where in there! It only seems to miss on No1 plug, took it out and all sooty( the one i put in) rest are clean. Next thing to try is a different lead, but how reliable are the coil packs? before deciding on the big job!