I'm currently doing a trial fitup on my 1943 WM20 to make sure everything aligns correctly before doing the final paint. While mounting the gearbox in the engine plates, i couldn't work out why someone had fitted extra spacers to the gearbox mounting bolts. At first I thought I had the wrong gearbox, but the box is stamped JHL 66-3030 so I figured it was about right for my bike. After much headscratching, I noticed that the gearbox case has been damaged/modified by removing the supporting webs on each side of the mounting bosses. Hence the need for the additional spacer on each mounting bolt to take up the additional space between the engine plates. Why Why Why would someone do this??? The additional spacer between the plates is 12mm wide. There's also a custom spacer at the gearbox adjuster that is 15mm wide.
Does anyone see any potential alignment issues with this setup? eg primary chain or drive chain?
It might be better to find another gearbox case, as that one is seriously weakened. But if you are going to use that one, I would suggest setting it in the frame, Temporarily add the clutch and see if the engine and clutch sprockets line up with a straight edge. Ron
I see the casting is also drilled and tapped through the mounting boss for the central gearbox adjuster...It is therefore probable that at some point it has been modified to fit either into either a just pre war B series frame or a post war 1946-47 B31...These machines have the central adjuster and narrower gaps between the gearbox mounting plates...Where are you based?.....Ian
As Ian has highlighted it’s been modified to fit the “ narrow “ gearbox plates / box on the 46/48 B series
That box perhaps wasn’t the greatest being based on a pre war design - so when they eventually started giving bother - military surplus boxes were a plenty & cheap
I should think you could come up with a gearbox case relatively easily in your part of the world....Many of the M20s we lent you weren't sent back...!!:laughing: ...Ian
