Thinking about finding an oil-bath filter for the Bajaab. Then noticed this centrifugal pre-filter for a Farmall Cub. These are pretty cool. They’re still used on tractors and trucks today, although they look a lot different now.

The method of operation is pretty simple. The air is drawn through the louvers on the bottom, which being arranged in a circle, spin the air. The dirt in the air is spun the outside of the filter, and collects in the “dead” air of the jar. The clean air continues down the intake stack and into the air filter. The centrifugal filter gets the bigger particles out of the air so they won’t clog the main air filter up fast. Here’s a patent drawing:

Modern ones work on the same principle but are more efficient I assume - at least they can trap a lot more dirt before they need to be cleaned out.


As for the oil bath filters... I was seeing if I could find one of the heavy duty ones for a VW Thing, but man, are those expensive! Given how few VW people run them, I wouldn’t have thought they’d be worth much. Also looking at Mercedes units, but again, pricey. Most car-style ones won’t fit on the Saab because there is not enough space over the engine, so I’ve been looking for models that mount to the side of the engine.

Also looked at tractor and truck units, but most would take up too much space under the hood, or be too restrictive (the Farmall Cub units are small, but those only needed to move enough air for a one liter engine).