Strange A10 Crankshaft

[Servodyne]

Hello everybody,
I've recently bought a large journal A10 crankshaft off ebay, but I'm now wondering what I've actually bought as it is totally different to any that I've seen before. The flywheel isn't attached with the usual 3 retaining bolts but appears to be 'shrunk' on with 3 retaining threaded studs that are flush with the outer surface of the flywheel. The question that concerns me is will it be compatible with a 1957 swinging arm A10?
Cheers Jim
   

[JulianS]

The crank is the early large journal item fitted to the Road Rocket until about July 1957 when it was superseded the version with radial bolts and removable sludge trap tube.

The service sheet below deals with compatibility of big end shells for the 2 cranks.

[Servodyne]

Thanks for the reply and information. It looks a though it's actually the correct crank for my 1957 Spitfire engine. I suppose the next question is; what's the difference with the big end shells and why can't the later ones be fitted to the earlier cranks?   

[JulianS]

The difference was probably due to the crankshaft material. The service sheet is ancient and later shells might be OK. I would ask someone like SRM about them.

Below a parts bulletin giving the engine numbers for the change. Unfortunately a poor copy.

[Servodyne]

More and more curious. Could it be that the earlier road rocket cranks weren't up to the job?
Is that why you don't see them around these days?

[JulianS]

I think the change was an improvement with the fitting of the removable sludge trap, of course the numbers of the older cranks were limited compared to the later version. I dont recall hearing or reading of any problems. It might have been more economic to produce but who knows.

[Servodyne]

I was hoping that you was going to say that. In theory the smaller sludge trap should make the crank stronger and with effective filtration make it far less likely to fill up with sludge.