Hello everyone!
I'm a reenactor and motorcycle enthusiast from Hamburg and I need your help! - Please! 
I bought a BSA M20 about two months ago, and still waiting for it to arrive. Since then I'm gathering informations as many as I can.
I'm not really familliar with bikes like this, in fact it's my very first "older" bike.
I sold my lovely 2007 Ninja ZX6R to finance the BSA, so you might understand I'm really serious with this. 
Also, keep in mind I'm riding for only 5 years in total, I'm 24 years old and since I'm a chemist I'm definitely not an experienced mechanic at all!
First things first. This is the bike I purchased:
http://www.abload.de/gallery.php?key=qqQwVBJ2
It's supposed to be from 1944, I bought it from the US, was at least 30 years in the hands of the pre owner and seldom ridden. Basicly, that's all the info I got there...
Now, because I'm also (trying) to re-enact, I'd love to have the M20 not only in working order, but also in the most "authentic" and "original" look, as I could possibly make. That IS my goal.
I spent a lot of time researching, comparing pictures and dates and so on, but I have the feeling there're so many details I simply can't find out for sure.
For example, I know you guys have the knowledge to preciecly identify an indian made copy girder fork from an original one - just by a picture! But actually that is not my concern because I have tons of other questions.
So here we go:
- First of all: Is that an odd colour mix for an military 1944 M20?
It appears to me, the main frame, both rims, fork, most plugs, levers, speedo, main and fieldstand and the complete handlebar are painted black.
As you can see, only a few parts are actually some kind of olive.
I looked through a lot of BSA pictures, and there are many different colour shemes. (Yes, I checked for the colour information on the main page here). Still, I have not found an original picture of a military BSA with a mixture of black and olive, as mine. Most of the original pictures show them in "complete" green. Most modern restorations are complete green aswell...right?
Also, notice the big black cover on the engine. I've never seen this on any pictures. What could it mean?
- Where has the C-number table gone? I'm trying to figure out, what C-number I can choose, regarding to the frame number (see pictures). Unfortunately the table vanished from this site. Why? 
- Where to put the C-number? Obviously, there's a pedestrian slicer on the front fender. I saw so many pictures from M20s', it's all mixed up I guess.
Does it mean, this particular m20 was in civilian use before the war? Or not? Where should I put the C-number on? The Tank or the slicy plate? Should I cut of the plate then, if it makes it more "authentic" to a military 1944? I'm really confused with this ... 
- If I'm seeing correctly, the white "mud flap" on the front is missing. Is tha a must for a military 1944 m20 ?
- Is the lamp size correct for 1944?
- Why is the horn located near the back wheel? I have found very few pictures of M20s with the horn on the back. Most of them got it on the front of the frame. Why is that, and when was that changed during the war?
- What are these two red reflectors besides the tail-light? Turn-signal indicators, or just reflectors for US-Street standards? Never seen these on pictures too. Should I just remove them?
- Is the tank I have the "cut away" tank? (I suppose, the edge of the tank was cut of for that massive hose from the external air filter, which I don't have). Is that ok for a 1944 M20?
- Do I need an air filter on the carb? Is it not recomended to ride without an air filter on these bikes? Did military bikes had no small air filters, except the vokes filter?
- When I read this correctly, frame and engine number do NOT match. I don't care that much though, because I can't do very much about that, right?
Do you see any more things that are odd, or don't fit into the year 1944?
Is there anything suspecious on this M20? Technically it seems to be in quite a good condition, just by looks. What do you think?
Unfortunately the bike did not arrive yet, so I can't take a more detailed look at it.
I have a ton more of newbie questions on hand but I think that's enough for now!
I would really really appreciate it if you guys give me some advice on my questions! thanking you in anticipation!
By the way, this is me:
http://www.abload.de/gallery.php?key=sXISw4Uo
I apologize for my faulty english, I did my best.
Regards,
Thomas
email (option): tomekk-13@web.de
Hello Thomas
Welcome to the forum, there are people on here who will be able to answer your questions with no problem. Me, I might have one or two problems answering them However, the easy one is that the bike would have been just the one colour - even though it does look quite smart as it is. The black on the timing cover would not be correct either. It could be that it is just painted black or it may be that the paint is hiding some repaired and filled damage, but I hope not. You do not need an air filter on the carb, a lot of us run without the Vokes. The 'C' number should be on the tank.
I will step back now and let the experts chime in.
It looks pretty good and complete so I hope you have some good experiences with it.
Duncan
Hello Thomas, welcome to the forum.
I think it looks pretty good, you are right the frame and other parts shouldn't be painted black but that's was most likely just the previous owners decision.
There are a few minor parts which aren't correct for WW2 but it will be a nice easy job to put it back if that's your goal.
The front and rear number plates are both post war military additions and can be removed and the census C number should be on the petrol tank.
And I'm not sure if I can read the frame number properly from the pictures but if you tell us what it is we should be able to tell you the census number.
Rob
email (option): robmiller11(at)yahoo.co.uk
Hi Thomas,
Just a few answers to some of your questions.
You are correct with the horn, your bike should have it on the front engine mount. Early bikes had it fastened to the seat spring bolt.
I did notice the kickstart lever looks to be at the wrong angle. I would have thought that this needs looking at. It may have been put on wrong, or could have a broken return spring.
Enjoy your bike when you receive it
Regards,
Dave
email (option): jeepfinger@blueyonder.co.uk
Thanks a lot!
I never noticed the kickstarters position on the picture before.
What happens when the kickstarter spring is worn? Does the kickstarter crank flop around? Won't I be able to start the bike at all?
I have to dismount the gearbox completly to take of the cover from the gearbox, in order to replace the worn spring. Is that correct? Sounds like a difficult procedure...
If I have to replace the spring, I have trouble identifing the "right" one. I need part 66-3058. How do I know, what gearbox type I have?
Which one of these springs would fit?
http://www.ebay.de/itm/BSA-M20-M21-B31-B33-KICKSTART-RETURN-SPRING-66-3058-/300999925036?pt=UK_Motorcycle_Parts_13&hash=item4614fe5d2c
http://www.ebay.de/itm/NEW-KICKSTART-RETURN-SPRING-BSA-B-M-PLUNGER-M20-M21-/120801788955?pt=UK_Motorcycle_Parts_13&hash=item1c2059041b
Both say in the describtion, part no. 66-3058. Though, the second one says "not fitting for M20 WM.
What is the difference between WM, M and B model ???
Regards,
Thomas
email (option): tomekk-13@web.de
Thomas, have a look at the Technical Info pages on the website! There is a wealth of information available, also for the gearbox
email (option): viaconsu [at] planet'dot'nl
Kickstart return spring just that.. You should be still able to start bike, but lever will flop around (bungee straps always come in handy in those cirumstances) The gearbox end cover will come off without removal of gearbox. The spring is located inside this outer cover..
Congratulations by the way.. You'll get more fun out of riding the M20 than on a riceburner in my opinion!!!
email (option): ian@integsi.com
Hi Thomas,
A really nice bike with all difficult parts present. According to the framenumber page your bike must be from 1941 instead of 1944. So the colour could be brown or OD.
best regards,
ramon
email (option): noahlevi6@hotmail.com
Hi,the kickstart may just need the cotter pin turning round,if the spring was broken the lever would hang down.
Cheers Rick
email (option): richardholt@rocketmail.com
Allright, thanks for the input guys! Keep it coming!
I hope the M20 arrives next Tuesday. Then I can finally check that stuff first hand.
Hmm, I'll check the kickstarter and this cotter pin. Thanks for the advice!
As for now, it looks like I leave the colour the way itis. As I stated earlier, I already looked through a ton of photos. Including the ones on this page. I saw all kind of colour configurations, that's why I asked if anyone saw this black/green combination anywhere else. Maybe one day I'll strip her down completly and repaint everything
I assume this bike consists of parts ranging from 1941 up to 1944 at least, right?
As far as I know the lamp size, the panier frames, back seat, field stand position and cut out tank are more on comon for 1944.
I guess it's some kind of zombie m20 when the frame is from 1941 and the front and rear license plate holder are from civilian use - combined with all the other parts?!
Oh and I still don't know what to do with these red reflectors on the rear...
I think I just remove the front license plate too, and paint a C number on the tank, just as you recommended.
The frame appears to have the number WM20 37684 stamped on it.
There was a nice table on this page:
http://www.wdbsa.nl/tanknumbers.htm
Where can I find it?
€dit: sorry, I keep swaping "page" and "site" very often ...
By the way, I think this bike looks very similar to my M20! The horn is on the same spot too ...
http://i165.photobucket.com/albums/u58/HinniB747/004-1.jpg
email (option): tomekk-13@web.de