Hi All,
All relevant points, what I was saying was that the leaking gasket (more than once) caused over heating which contributed to the burnt valve!
Valve/seat recession, excessive cutting/facing/grinding is more gradual,
Excessively wide seats lead to burning valves due to the relative drop in spring pressure as the area of the valve seat increases,
After many uses the head bolts also stretch and lose their elastisity,
As well as new head bolts I spotface the seating area of the bolt heads and make special 0.100in. thick washers which are 0.750in. OD, this spreads the load over a wider area,
The original bolts and washers dig into the alloy head surface and also squeez the alloy in around the shank of the bolts, so affecting the torque setting!!!
On composite gaskets, (on Triumphs anyway) they normally require several torqueing down sessions, after first startup, 50 and 500 miles. Real PITA
Regards
John O R