Can someone please identify the pictured girder forks. I have been told they are 1936 M20. They will not fit the wheel of my WDM20 1942. they are 13.2 cm at the base, my wheel needs at least 14.2 cm.

http://i1058.photobucket.com/albums/t408/banderson323/Forks3.jpg

http://i1058.photobucket.com/albums/t408/banderson323/Forks2.jpg

http://i1058.photobucket.com/albums/t408/banderson323/Forks4.jpg

http://i1058.photobucket.com/albums/t408/banderson323/Forks1.jpg

I would guess at an M23-M24 but when did they stop with rubber mounted bars?
Is your friction damper in the right place?

Ron

email (option): ronpier@talk21.com

M20 wasn't sold until 1937 ... But for me they do indeed look like 36 forks suitable for the 500cc size bikes, the axle width is suited to the "brakeplate type speedo drive" bikes.
The tell tail sign is the sparkplug holding hex below the bottom pivot (to hold one hex while you undo the other hex of an 18mm sparkplug while you disassemble it for cleaning) that's only in the pre 37 forks (pre M20). Unless im mistaken, they dropped that hex when plugs changed over to 14mm.
I can check the part numbers for you if you can tell me them, I have all the part numbers listed for all those 30's forks.

Are the front tubes parallel down their run?
M20 (just for reference) start with a 5" gap & increase by about 10mm at the lower end.

I'm not good with this pre war stuff Fred. I was trying to make them later because of the rubber mounted bars. Of course they could be some mixed up parts. I dare say the bottoms could be gently spread to take an M20 wheel with speedo drive. I quite often do it with a length of studding, two penny washers and two nuts in the wheel spindle slots pushing outwards to get a mudguard between the forks without scratching it. Ron

email (option): ronpier@talk21.com

Thanks, Yes they are 5" at the top and 5 2/8s (10 mm difference) at the bottom. Am I wasting my time trying to fit them to a 1942 wdm20?

email (option): banderson323@bigpond.com

I can get the wheel in by shaving down the bearing spaces but it's a tight squeeze and the wheel looks off line from top to bottom (vertically). And the brake plate has no cap at the top and a larger cap at the bottom.

email (option): banderson323@bigpond.com

We posted simultaneously Ron, I agree I would carefully spread the bottom out if it were me, the legs aren't parallel from standard so structually not a huge bodge considering how many girder forks in use are probably a bit bent anyway.

I would use them.
Ive measured distance between top & bottom pivot centres (on blades) on M20 its 210mm.
Also regarding part numbers the 37 on forks (M19,20,21,22,23) start 66-****
The pre 37 forks I think yours are, will start 15-****
So easy to see which they are (confusion lies in the fact BSA list complete forks & just blades with different part numbers but 15 or 66 is the best clue.

I must also point out that its wrong to assume bike frames & forks have had a "Clean" life. After 75 years its highly likely the bikes been dropped, hit in accident, wrong wheels fitted etc etc
Never assume they are as left factory & compare with as many others as possible if you can, the wheel needs to run inline with the headstock. & could itself be laced with an incorrect offset.

...also, over the years ive noticed damaged fork bottoms, for that reason I pay alot of attention to how accurate the fit is of the "turned protruding part" of the wheel nut it the corresponding area of the fork bottom....

Thanks again. The numbers do start with 15-5252 etc. I did have the wheel restored you maybe right the wheel could be the issue.

email (option): banderson323@bigpond.com

Bryce,

Fred is right these forks are 1936 or earlier for 500cc bikes. They also had the rubber damped yokes. If the hexagon is for a 14mm spark plug they are Empire Star, Blue Star or J12. if the hexagon is for a 18mm plug it is for the bread and butter SV and OHV singles.

regards,
Leon

email (option): leonhop3@planet.nl

Does anybody know what year exactly the rubber yokes appeared ? Was it 1935 ?

Yes, 1935 is the first year of the rubber mounted top yoke.

Leon, does your J12 have 14mm plugs? Mine has 18mm plugs.

Hi I have a 1935 W35-7 and that has rubber mounted handlebars, same as my 1936 Q8 Empire star, both are 500cc bikes, also same for a 1938 M20 I have.
Interestingly, there is reference to a Hex for spark plugs in this forum subject on the fork, my 1936 and 1938 forks do not have this. The 1936 Q8 forks have been confirmed by Jake Robbins (the girder fork repair specialist) as 100% 1936 Q8 Empire Star when they were refurbished.( he had to make thin bushes for them ).
My understanding was that the 1935/36 heavyweight 15- series forks were not bushed for the links, but the later ( 1937? ) M20 etc bikes are bushed as per factory design. But basically same geometry.
Certainly the 1935 W35-7, 1936 Q8 and my 1938 M20 are all offside front hub speedo drive.. I would agree that many years have passed since the bikes were new, so they could have been modified/upgraded/repaired etc by previous owners.

Rgds Dave

The top fork blade grease nipple on pre 37 blades appears further round towards the spring & the speedo mountimg lugs are thicker outside diameter & shorter with threads running almost to the through bolts, so it seams when replaceable bushes were added the lugs had to be made longer as the only thread then available would be equal to just the length of the lug itself.
So maybe the speedo lug difference is the giveaway if for eg the sparkplug hex has been removed for some reason on a set of forks.

As an extra piece of info.. the 1936 Q8 uses 14mm spark plugs. The 1935 W35-7 uses 18mm, however I have a late spare head with a 14mm spark plug? ( Of course it could be so late that its a 36, but I am not so sure on that, maybe a head used right at end of the 35 model year).

Rgds dave

Alot of heads had inserts fitted to take 14mm plugs & not always obvious until the heads cleaned up for restoring.

I did check this previously, no insert.. its a mini mystery, good head though.

dave

Has it got a part number on that head ?

Hi Fred, cant tell you the P/N at the moment, I am 200 Nm offshore USA South of the Mississippi, will not be home in the UK until mid August, will take a look and report then..

dave

hi,excuse my ignorance ,with the spark plug reference,
are we talking about the hexagon hole shown in pic 4
or the thread in the forward pointing protrusion which i thought was for the early rod operated brake system.
im sure i saw a post that a 14 mm plug will screw into
this,if it is no longer used.
cheers rick

email (option): richardholt@rocketmail.com

Yes, that Hex hole in pic 4, on 18mm spark plugs for eg the two hex sizes to take the plug appart for cleaning are 13/16" AF & 1" AF, one is held in the hex hole in the forks while force is applied to the other, its as good as having a vice. .... Actually no, I can think of some good vices

Hello all
I am trying to restore a 1934 W34-7 and have been reading this thread with great interest.
My forks don't have the hex and the part list does not show it either. So was that only forks post 35.
Also anyone have any good photos to share to aid me with my restoration
Thanks Darren

email (option): Darrenacartwright@yahoo.com.au

Yes your 34 bike has the forks with no hex, it also has a different type of lower pivot faceplate ( on blades where the damper anchors).
The forks on yours have a shorter distance on the blades between top & bottom pivot centres so the links tend to run parallel with each other.
Its reported that for 35 when that distance was increased (some models 36) it was done to keep the wheelbase the same during fork travel, I think actually the reason was more likely to keep the wheelbase the same during BRAKING (anti dive) because the BSA girders from 35/36 on had links that "splay" when viewed from the side. That gives them the best chance of not rising OR falling under braking.

I agree with Fred no hexagon in 1934, but if I am not mistaken (I am at work and don't have the parts books at hand) your bike would have had one of the headlamp brackets with the hexagon in it. It was a flat strip as opposed to a tube.

Regards,
Leon

email (option): leonhop3@planet.nl

Yes Leon, I see it in the 34 book 15-8997 lower lamp bracket with hex hole at its centre.
I didn't know about those, plenty to learn

I've been to jumbles with Leon. He has every part number for every 1930's BSA, in his head Ron

email (option): ronpier@talk21.com

Very handy Ron
I carry on my phone a huge amount of reference info for eg all 30's BSA original parts books with pictures in. PDF format (over 300mb) that's extremely handy at jumbles ... In fact Ive never owned a home pc or had home broadband.. everything I do online/write here is on my phone, technology is amazing ... As long as I don't lose my phone