HI MATE ,
GO WITH WHAT PAUL SAYS BUT ALL 2WD COSWORTHS SUFFER FROM PISTON SLAP THAT WAS OVERCOME ON THE 4WD AS THEY OFFSET THE GUDGEON PIN ON THE PISTON TO ELIMINATE THAT.IT WILL GO AWAY AFTER A MIN OR TWO AS THE ALUMINIUM PISTON EXPANDS IN THE CAST BLOCK.
CHEERS MARK