All the bearings in the CRF engine are steel rollers. If you've got steel (magnetic material) in the filter, you've got an issue. During manufacturing there is a lot of aluminum that doesn't get cleared away and ends up in the filter. Thats not that big of a deal. The transmission doesn't have a filter so you've just gotta watch the tailings coming out in the trans oil when you change it. Everything in there is also cast iron or steel. Except for the basket and hub and drive cushions.