Our experience has shown that additional breathing is required for all offset crank engines. An in-line Positive Crankcase Ventilation (PCV) valve is recommended along with a vapour condensation chamber that can be easily drained. The breather line should exit well past the end of the rear tire. A breather line run from the timing hole of a T120 or T140 twin that is connected to the existing breather lines is also recommended. Various modifications can be made to the breathing system on Norton engines. On pre-unit BSA and Triumph engines a breather that connects to the crankcase between the barrels and the igition unit is recommended similar to the image shown below.