I have an interesting problem: the #4 spark plug is covered in a light gray colour. The other plugs are normal; light brown. The threads of the offending plug appear to be covered in oil, while the others are clean. Two things might explain the grey: malfunctioning injector causing a lean mixture or blocked water passage resulting in overheating (head gasket is intact). These have not been looked into yet. What about the 'oil'? Do I need a valve job? I'm pretty sure I don't burn any blue... Any help is always appreciated.

P.S. Are there any good websites about Volvo cylinder heads (405 and 531) and their modification? Been to 'tractor pulling center' and Paul Grimshaw's sites, and a host of others, but I need more. Puma racing is excellent, but direct experience with Volvo heads is what is needed.

Thanks

ben