A few pictures to help explain the subtle differences between early and later engines. All from my junk pile, as found.
1 Longstroke crank has a distinct cut out between the crankpins, shown here beneath a shortstroke A7 crank for comparison. Timing side journal, crank nose and drive splines are the same for both cranks. Later crank has wider flywheel, and is also marginally longer, pictured here with the inner race still in place.
2 Longstroke crank has extra weight at the flywheel side edges, opposite the crank pins. This is absent from later crank.
3. Crankcase drive side bearing location, showing small recess to accommodate oil slinger, which goes in first before the bearing. This recess is also found on pre-oilseal later A7/A10. Bearing used here is a different size, so slinger and bearing location diameter also changes.
4. Oil slinger and bearing in place. It's the idler shaft visible thro' the bearing bore, due to the camera angle.
5. Close fit between correct drive sleeve and Longstroke crankcase or later pre oilseal shortstroke case. Oilseal type drive sleeve is smaller. Fitting the wrong sleeve results in a gap together with crankcase oil transferred to the primary.
Swarfy.
