91.46 mm is the size of the over size pistons for the 616 and 617 engines.
Add 0.04 mm and you get the size that the cylinder should be machined to for that piston.
91.50mm is the size of the cylinder and 0,04mm is the clearance of the piston.

I used the new style head bolts on my 76 240 and never had a problem with them.

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76 240 D. Bought in 1998 for $25.
85 300D. Got it for free with a bad engine. ( Sold )
60 Unimog 404. What was left of it, was given to me. Now powerd by 617A.
88 560 SEL. Bought without engine and trans. Now powerd by 617A.
67 250 SE. Cuope. For resto or sale.
64 220SE. For resto.