Series One/Series Two

[welleyes]

Other than bigger bores and longer stroke crankshaft, what was the difference between the two engines? Or to put it another way, what do they have in common? Are the main castings different? What was different about the con rods?

Stuart Tallack

[davidwheeler]

Heads are interchangeable.  Blocks certainly look the same.  Early rods are Duralumin and run direct on the crank journals, later ones are steel with white metal in bronze shells.  Possible to fit modern shells by building up the crank a la Harry Manning.

[ben]

As far as I know all Aprilia rods are aluminium alloy except where owners have had replacements made especially in steel.(like David!)
S2 cranks have smaller big end journals than S1 ones,I assume in order to provide some of the space needed for the thick-wall shells.
Hence using modern thin-wall shells in alloy rods works best with an early crank.
The man with the data is Ken Cousins but he is not on the forum.   See membership list for contact details.

As for other differences between S1 and S2 engines----what can you tell us Blue Sky?

When I put together my spare S2 engine I found that the oil feed pipe for the main bearings did not fit as the outer feed fittings were not far enough apart.It made me wonder if the centre distance between the cylinders was greater and I was maybe using a S1 feed pipe. My attempts to confirm this by measurement have been inconclusive!