The 2 and 4 lobe sprockets are completely different....(as is the matching part of the cam, the spring, the nut and the crankshaft sleeve)...The 2 lobe sleeve has wider splines externally, the sprocket cam surface is wider and only has 2 'high points' not 4, and the cam form is more gentle than the 4 lobe type...It's worth noting that the 2 lobe cams were also fitted to the A7 nd A10 but for those models the crank mainshaft is a bigger diameter so those sleeves won't fit on the single cylinder cranks...
The most common type for the singles is the 4 lobe type and it's probably best to stick with that type as there are far more second hand parts available...The 2 lobe version was only fitted to later, pre alternator, swinging arm model OHV singles and the crank sleeves in particular are much less common for that reason....Ian
