Hi Glen,
I have not found anything in the Douglas Handbooks which specifically states which side the flattened part of the spindle goes (and therefore where the locking washer 1404D, in the 1925 parts book picture, goes). I suppose it might not really matter as all it does it stop the axle rotating? But I guess there could be a subtle reason why it would be placed on one side rather than the other? Also when Douglas manufactured the hubs I assume they would have most likely manufactured them all in the same orientation? When re-assembling a hub after maintenance I guess it would be a good idea to put the axle back in its original orientation ? Maybe someone knows the answer to this?
I found the attached pictures of the hub from the 1916 and 1925 versions of “The Handbook of the Douglas Motor Cycle”. Also a picture from the 1920 Peace Program Brochure which appears to be the same as the 1916 version.
Douglas state that the hub cup lock ring should always be fitted to left hand side of the forks, seen from the saddle (I assume that also means that the hub cup lock rings will be on the same side of the bike front and rear). The adjustable bearing cup is the one with the left hand thread and is usually stamped “LH”. So my understanding is that the left hand thread cup, marked “LH” goes to the left side of the bike when sitting on the saddle looking forward.
In the pictures of the hubs, the spindle locking washer 1404D, in the 1925 parts book picture, is shown on the right hand thread cup side (fixed cup side, marked “RH”), so following that, the flattened part of the spindle goes to the right hand side of the machine when viewed from the saddle.
I would be interested to see if anyone has found this written somewhere in the Douglas literature, rather than relying solely on what appears in their pictures.
Hope that helps,
EDIT:- I just noticed that in the 1925 parts book you can see the flats on the spindle in the picture of the rear wheel, it is on the belt drive side.
Cheers
Hutch