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I am rebuilding my 1964 Kadett engine. I can tell it has been rebuilt once before becasue the pistons are ovesize for sure but what to all the numbers mean on top of the pistons? I read in one of the manuals that ther should be 2 sets of numbers, one is what the pistons were and one what the pistons are... What are your thoguhts of these pictures? Are these 73mm pistons or are they 72.99mm pistons in a 73mm cylinder bore? and what about the 0.010 reference?

Piston.jpg Piston.2.jpg
 

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Opel Rallier since 1977
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1,217 Posts
A difference in .01 mm (which is 0.0004") does not make sense for the 'before and after' sizes..... you won't be taking out 0.0004" with boring.... even a light hone will take that much out. And that small amount does not make sense for used bore taper numbers.... only for a fresh bore.

A SWAG: Maybe it is the range of bores for which these pistons will meet the standard new piston-to-bore clearance. This would make it easy in a volume assembly situation to measure the bore, and then pick a piston off of a rack to nicely fit.
 
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