Also check piston to head clearnce
Hi Paul
Glad you got the head off. Are the piston tops flat or domed? If they are domed check to see how much clearance there is piston to head. Did these engines have or change from flat to domed piston?
Reason I say this is that when had to replace the head one my HUP the new head was ment for flat top pistons but the engine had domed piston I replaced the pistons.
Having said all that my bet is on Greg's theory done to allow the engine to burn lower octane fuel.
Cheers Phil
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