substituting a large journal crank for a small journal crank

[Guy Wilson]

Some of you were following my 'my small engine rattle' post that transpired was terminal big end failure on my '55 Gold flash. It had a small journal crank. My spare engine had a large journal crank. I can't see any obvious reason why they are not interchangeable and the large journal crank would fit in the original small journal crankcases.
Is this the case or am I missing something fundamental ?
Guy

[Klaus]

Hi Guy,

you are right. The crankcases are the same.
Only difference is the prefix showing whats inside. D is for big journals C for small.

cheers Klaus

[Guy Wilson]

Thank you Klaus, I'll go the large journal route for now. I can't afford the replacement small journal con rods  at the moment...
Guy

[muskrat]

The only problem I struck in doing that was the con rod nuts rubbed the cases. I shortened the nuts a mm and all was good.
Cheers

[Guy Wilson]

Good to know!
thanks
Guy

[Dean]

I have just made the same mod and I also had a probelem with the big end nuts catching on the cases. A couple of minutes with the Dremel to remove a mm or so from the inside of the case and all is well.

[Guy Wilson]

So what the general consensus? Remove metal from the case or shorten the bolts? The bolts are surely cheaper to replace?
Guy

[trevinoz]

I would put the crank into the case and see what happens first. I have fitted LJ cranks into early cases with no problems.