Aprilia Engine Numbers

[Martin9]

My 1937 Aprilia No 38-3999 has engine No MOT:99 30593 which I understand is a 1496cc engine.

I've been digging on the forums to find when this engine was built but without success: can anybody out there help me with this information?

Many thanks.

Martin

[DavidLaver]

I think of the "small" and "large" engines being pre and post war.  Anyone know quite when and why the change was made and what else differs other than capacity?

[GG]

In Storia Della Lancia, Rosani has the changeover in 1939. Drawings for the 438 were begun in late 1938.

In the larger displacement engine, bore and stroke were both revised, from 72x83mm to 74.61 x 85 (bore and stroke). Conrod bearings increased in diameter.

In order to fit the larger pistons, the cylinder centerline moved a bit further out in the block and the bore angle slightly reduced. In the crankshaft, the crankpin offset angle was unchanged, but conrod bearing was increased in size.

[ColinMarr]

Apart from the engine numbers stamped on the block, I think the only distinguishing features are that the later larger engines had a spring clip cover over the flywheel inspection port and a larger beefed-up aluminium bottom hose connector. The cam box cover on later engines had a cast-in fitting for a top stay. Such useless knowledge still clutters the brain …. !

[Martin9]

Many thanks, Gentlemen,

What interesting and varied information and yes, I certainly do have the larger engine.

Is there a schedule anywhere, as there is for chassis numbers, that shows engine numbers by year?

Martin