A friend has a small engine machine shop (he even does replating) and he said that Maicos have by far the strongest cranks of any single cylinder engine he has worked on. When he has to re & re a rod on a Maico crank all his employees hide.
Maico cases,like the old Spanish and British bikes, are pure sandcast aluminum. The Japanese cases are diecast and are "thinned" with impurities like zinc.This is why Japanese cases are always painted - to prevent corrosion.