THanks Jens for your explenation.
I know the technique of lapping, but have not mastered it yet on my lathe

I will make a head with contrapiston and O-ring instead.
Still puzzeling what engine i should use on my latest project a no-cal F8f. The 10FP or the Magnum XL15 (both _to be_ converted to diesel)
Best regards,
Franck