ISO Metric screw thread
Overview of ISO metric screw threads M3 – M30. Commonly used screw threads on 1948 – 1969 BMW models are M6x1 coarse, M8x1.25 coarse and M8x1.0 fine. The length of bolts and screws is measured like this:
Reading spark plug faces (Bosch)
A visual inspection of the spark plugs can serve as a good indicator of the condition and tuning of the engine. This Bosch sheet may help to identify the possible cause in case of trouble. (click to enlarge)
Overhaul of a 2-cylinder crankshaft
The photos are a compilation of the work done on different crankshafts: R67/2, R60/2 and R69S.