I'm trying to get some girders situated / fixed up properly and I believe they may be earlier than M20. They are no doubt BSA as they are stamped and so are the bits and pieces. I looked at this diagram: girder fork illustrated parts and that's how I came to the conclusion mine are probably earlier. My bottom links are different and so is damper knob. The only thing obviously missing is the lower, rear link bolt. The main thing I'm wondering about are friction disks etc. and what else may be missing. Hoping somebody here can compare with theirs and chime in.
Well the good news is that there was only 1 friction disc listed from 1935 on so good old WM 20 ones will do you fine. The forks would appear to be M series and if the wing nut spindle bolt is correct from some time prior to 1935 when the M , J & G series got the full round type of adjusted while the B & R retained the wing nut till WW II. However there should be a support pin up the middle of the spring. BSA only made 8 different girders and each one is quite distinctive. Having said that parts can be swapped from one type to another & as they are pushing 70+ years old there is no reason to believe that they are as they left the factory. Please get them crack tested before you put them into use. They are prone to crack at the joint between the forged lugs & the tubes and in particular the front straight ones ( one appears to be bent on yours ).
What leads you to believe they are M series? They look different to me than the illustrated parts link above. In that picture, the headlight affixing points, integral with the fork, are different from mine. Also, because my links are different (they don't have that approx. 1" round protrusion on outboard side) I can't use the friction discs pictured - the hole is too big. The inner hole of original friction discs would have been about .5". I don't know what they are, part numbers 15-5246 and 15-5244 but they would be of no use either. If I were to make friction discs, where would they go - inboard side of link and outboard side of headlight fixing point? So, sandwiching that silver piece between link and headlight fix?
The most obvious is the mudguard support. Some were on the front of the cross tube, some on the back while others like yours come from the middle. Then there is it's shape & the fact that it is there at all.
Next there is the shape of the link plates.
Your spring is the double tapered which makes the forks either medium or heavy weight.
Then there is the mudguard stay/ front stand lugs intergral with the bottom forging and the absence of any other lugs on the legs.
Add the brake anchor plate & it is signed sealed & delivered.
The drawing in the link is the last version and those headlamp mount brackets are flat plate which was stitched on with a couple of welds and dates from around 1934 / 1936 depending upon which model when the wing nut was replaced by the adjustment disc.
You need 2 friction pads one goes between the fork & the chromed link on each side, which hopefully will move the left plate out far enough to clear the back tube.
To be definitive I would need you to measure between the centres of the holes in the link plates and tell me which ones are threaded & which ones are plain . I do not email from this computer but if you send me a pm I will send you a couple of pages from a mid 30's parts book with the measurements.
Overandout, thanks for trying but, those are a no go with my links. For mine, inside hole needs to be 13-14 mm (1/2"-9/16") and outside diameter about 6 cm (2 3/8").
BSA WM20, is this what you mean?
The measurement center to center is about 9.5 cm. I'm not sure what you mean about the threaded business. The bottom links, left and right have the same part number; looks like 15-8609. Sending PM now.
Got the message & sent the pages to you. You have it correct except you will need an imperial ruler graduated in 1/8". Any one else following this thread sorry but it it too much frigging around to get 16 pages on to this forum. Some link plates are threaded while others are just plain old holes. This will help you verify what you actually have.