I just rebuilt my crank to replace my snapped one I just swapped the big end as mine was good, I didn't take much notice of the roller length, simply rebuilding my good big end into the new flywheels then I came to fit it............it wouldn't fit, it had about a 1mm gap at the crankcase halves, then I realised that the Flywheel into my engine had been previously modified by reducing the little spigot that the main shafts protrude from, this is possibly why it snapped in the first place, possibly they didn't machine it correctly when the fitted the later crank and they possibly created a stress riser. I realised I didn't want to go through the pain of taking the big end back out and machining it, so I simply placed the main bearings on the broken shaft I had lying around and ground the bearing centre on my lathe with a Dremel. I just took them down to where the inner seal on my sealed bearing was removed from and it fitted perfectly. The moral here is that the later big end assembly which is wider will fit in the earlier crankcases without doing any harm. I just made sure that I throughly washed out and blew the bearing out afterwards.

email (option): davmax@ntlworld.com

I've mentioned this before Dave !!!! Post-war, the crank-assembly was beefed-up (though the design drawings of which I have the originals) are dated 1943............the change was not incorporated into production though until 1945-46..........

The complete Flywheels, conrod and crankpin are interchangeable between earlier and later units (cases) and vice-versa but not the individual components................

The pre and wartime crankcases are also much more "webbed" than later versions (more cutaways, less metal)..............

['The complete Flywheels, conrod and crankpin are interchangeable between earlier and later units (cases) and vice-versa but not the individual components...']

So they are only interchangeable if modified slightly?...or only interchangeable if the complete crank assembly is fitted...?

If the latter is the case does that mean the big end widths are different but the overall width of the two crank assemblies is the same?.. Ian

email (option): ian@wright52.plus.com

The post-war book of the Royal Enfield by Booker (service manager, Royal Enfield) in the Pearson's series covers all models of the Flea in considerable detail........this guide states that the complete crankshaft assemblies pre / wartime and post-war are interchangeable as complete units between pre / wartime and post-war crankcases (that were also beefed up a tad internally) but the individual component parts are not..........in particular the early crank assembly had 1/4" rollers x 21/64ths long whereas the post-war unit had the roller length increased to 1/2" length........

And from personal experience I have fitted the early crank assembly into later cases and vice-versa.......some light shimming may be necessary but all the clearances are detailed in the various manuals...........

Photos above showing the different crank assembles........post-war is "fatter" in construction..........

Mine has the early crank like on the left picture but the rod is wider to accommodate the longer rollers but it doesn't have the raised web at the side of the conrod like the one pictured right.

email (option): davmax@ntlworld.com