Got myself a bit of an unwanted challenge at the wkend! Driving along in my ST170 at 40mph in 5th, when all of a sudden, spark plug no. 4 decided to leave the cylinder head! The previous owner had cross-threaded it, so must have only been hanging on by 2 or 3 threads, which are now a bit... less than perfect! Got a new set of plugs and offered one up (or down) to it but it only went round 1 full turn once it was in before i thought i'd better not go any further.

I want to try tapping the thread with the head in situ then try again- does anyone know which one I should use, or the spec of the spark plug thread to find out?

Failing that I'll replace the head with either a low mileage 2nd hand one (which I don't have yet) or a new one. I don't want to do this myself so any recommendations who should do the work either near Stoney Stanton or Crewe?

Any help much appreciated,

Ken