The top and rear cover on this type of BMW engine were too high for this frame, plus they were full of all sorts of holes and BMW aluminum is difficult to weld, so I decided to make new covers. I started making a positive mold of the shape I wanted, using 18mm MDF. The first parts were slotted so that they slide into eachother, forming a strong base to clamp the rest of the pieces into.

The pieces were glued together with ordinary woodglue, and after drying I used a handheld beltsander to roughly shape the MDF, after that I used a hand sanding block to do the rest of the sanding, because a beltsander will very easily remove too much material.