Ariel Owners Motorcycle Club

I am rebuilding an engine from several parts and all was going well until I started assembling the gearbox. The idea was to rebuild it on the workbench and check its operation before putting it in the frame. I have rebuilt the gearbox and attempting to check it. First concern there is some lateral play in the main shaft when in neutral? but not when in first gear. With the end covers on gear selection is difficult neutral and first select ok but I am finding it difficult to select the other gears? Is the problem because the engine is not running? Any advice appreciated.

The gearbox on my late Arrow won't change gear unless I rotate the mainshaft
to help align the engagement dogs.

It has about 10 thou of endfloat on the mainshaft which doesn't seem to vary
whatever gear the box is in.