Thank you all for your answers.
For now I think we can have a relative confidence in this system: xxx-x-xxx (cc-year-serial)
For now I think we can establish this:
401 - FE400
472 - FC470
501 - FE501
553 - FC550
651 - FX/FE650
But here I have some doubts, for example I had here one set of cases, sent by Taffy, that had 473. They had to be from one 400 or probably one 470 but a different model ???
So I would say the first 3 numbers could define also the model or variation of the engine, not just CC of the engine.
Or probably the system is: XX-X-X-XXX (CC)-(model)-(year)-(serial).
So we would need more engine number to try to set this right.
Kris, this system only applies to 01-03, I think, so for the first generation until 2000 I think it's a different system.
I don't have here with me my older engines, but if I remember they have 2 numbers, one on the cases and one on the cylinder, maybe we will have to play with both ??
But it would be even more interesting to be able to understand the first generation of engine numbers, because there a lot of cases like yours, of owners that don't really know the year of the engine, specially with the older ones.
So to start that, we need engine numbers, of engines that the owners have sure of the year and model.
So please keep sending them