The BMW R12 motorcycle used oil filters that were very primitive in design. They were made Knecht, Mahle and other manufactures. The oil filters were a can design that was 92 X 83mm. The thickness of the oil filter was 1mm. They weighed 375 grams in total and was quite heavy compared to modern oil filters of today’s standards. Inside the oil filter is a spring that is covered in a cloth material. The wire of the spring was 0,05mm and the length was 100mm X10mm in dia. At the bottom of the can was a flat spring. This allowed the filter to be pressed up against the motor when you put the oil filter door back on.
1937 logo from MAHLE
The oil enters the filter by a small hole which is pressed onto the oil inlet on the bottom of the motor block behind the oil cover or the door. It would enter the tube under pressure and basically work its way back out of the filter by another small hole. This hole size was 1,5mm and was the size determined by BMW to create enough back pressure. This would give you about 2,5 bar of pressure at revolution of 250 cycles per min.
The old filters are not a wise choice to use now of days. With aftermarket kits out there, you can now use a modern oil filter with a new adapter created by someone from the BMW R12 community. These NEW adaptors have been tested and are working well. I highly suggest you buy a good filter kit from RRC tunning in Germany. They have a web site and its listed on the links page of this web site.
New oil filters brands must be used that are tested with the new adaptors, again PLEASE make sure you talk with someone who has used a new oil filter with their adaptor. Don’t just add any filter to the motorcycle.
If a filter is used which has the wrong oil flow direction, dirty oil will reach the clean smooth paper inside and the clog the pores sooner than expected. What happens is Filter resistance rises thus this decreases the ability to clean the oil. So it is very important that a new adaptor not only be able to mount to the small mouth piece at the bottom of the motor it also needs to be able to change the oil flow direction. Few filters have this correct flow design, again make sure you use the filter the seller has tested with his adaptor.
Here you have a new and improved oil Filter from RRC Tunning located in Germany. They are a specialist in BMW R12 motorcycles. Their web site is link is located on the links page.
The New cup design helps improve a better fit of the new filter in the area where the oil filter goes.
Below is an original BMW R12 Mahle oil filter. Notice the flat spring on top, this is what keeps pressure on the filter and hold it in place on oil nipple located on the bottom of the motor.
Another view of the Original BMW R12 oil filter. The flat spring on top keeps pressure on the filter when the door is on.
Here you can see the hole which the oil flows into.
Additional oil filter photos: