Sorry, my question was tounge in cheek.
I not trying to doubt anyones knowledge, not at all, but the problem is, when a specialist, Alfa Romeo factory trained (won top Alfa tech once!) tells me that these cranks cannot be reground it plants a seed I cannot ignore. I realise they can physically be reground and the material will be harder than the base metal but that does not mean it is good for thousands and thousands of miles.
The evidence does in fact stack up. The process means the "hard" layer is thinner than conventional hardening. this must make it more subseptable to damage which would explain why the Twinnie crank will not tolerate low oil, dirty oil and indeed "bruising" after a cam belt failure. Changing the shells after a belt failure is never an issue with other marques or indeed other Alfa engines, the V6 for example.
I am not preaching here, I don't know what the facts are for sure, but if I was in Jons position, I would be getting a good second hand crank, re-shelling, and be very confident of as good as new running.
All very good points.. indeed some high performance motorcycle crankshafts cannot be reground for a similar reason..
Exactly what hardening process is used on Alfa crankshafts and how does it differ from say a Fiat item??
I believe oversize shells are available from Alfa .. up to 0.75 mm ???
There is no doubt that grinding will reduce the thickness of the case hardening.. but this will not necessarily make it any less durable. The journals can also be re-hardened.. nitrided..
The problem with sourcing a used/ un-reground crankshaft is that it will have come from a scrap engine and even if it has not suffered a valve/piston collision.. oil starvation etc.. it will inevitably be ovalled to some extent.
I think it improbable that Alfa would supply oversize bearings if the c/shaft could not be reground..
Also I'm not sure that the twinnie is any less tolerant of neglect than any other engine.. no oil supply and it will wreck the bottom end.. that goes for any engine.. some twinny's burn oil more rapidly than most engines..
combined with lack of maintenance and you have a wrecked c/shaft.. end of story..
I'm just getting started on a full engine rebuild myself.. so if there's any secret knowledge out there (and not just heresay) regarding re-grinds..I'm all ears