Been meaning to post this,
If you're reading this I'm sure you realize the Sachs has 2 cranks, a 42mm and a 44mm "D" crank which gives more displacement AND higher compression, both final and in the case. COOL!
Obviously you'd want the D, and you can tell if your crank's a D if the engine tag says 49cc instead of 47, however sometimes the cranks may have been swapped before, or you're buying one randomly, or maybe you don't have the tag.
You CAN tell just by looking at them. The longer stroke is accomplished by pushing the big-end pivot farther out on the lobes of the crank.
On the 42mm "A" cranks (below) the big end pivot is about 2mm in from where the crank lobes begin to taper in.
On the 44mm "D"s the crank arm pivot is right at the line where the lobes start to taper.
as a side note, even many of the later european "B"s and other underpowered restricted models were made with the 44mm crank just to save money from making multiple different cranks for basically the same thing. they just got even MORE restrictive in the cylinders... These later B's will still say 49 (or sometimes strangely "50") cc on the tags