My understanding of your problem is that the piston is hitting the prechamber. The solution is to purchase shims that are placed proximate the shoulder of the prechamber prior to insertion. Mercedes sells these shims but it is very difficult to find someone with knowledge as to their existence. My buddy did this with his 602 after machining.

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Jovan

'84 (11/83) 190D 2.2 5-Speed; Silver/Blue; Motor No. 00354, 402k mi (340+kmi mine)

'89 Porsche 911 Turbo Coupe; Black/Black; 53kmi
'05 BMW 530i 6-Speed; 302kmi
'19 Range Rover; 30kmi