Resolved by:-
1) Changed the thermostat that was stuck
2) set the cam timing properly - turn engin ONLY clockwise to TDC- If you miss the spot turn another 2 turns for the crank before setting the cams.
3) The FLYWHEEL TIMING SENSOR ( Engin speed sensor) BRACKET was loose allowing the timing to be irratic, causing RAPID heating and cooling of the head.

HOPE this will help others.