I am new to the BSA M20 community. For the fuel tank for BSA M20's produced from 1942 onward, it would appear that right rear of the tank is flat, whereas the earlier tank was the same on the left and the right. Why did the 1942 - onward tanks have this flat area on the right rear? It also appears that there were several different styles gas caps made during production.

Comparing vintage photos and restored motorcycles, it appears that the early BSA M20 and the post-WWII M20 and M21 used the same style (shape) of fuel tank, but 1942-1945 used a different style.

Can anyone explain why?

email (option): questmasters(at)hotmail(dot)com

Check all the detailed info on this website http://www.wdbsa.nl/facts.htm

Buy Chris and Steve's book https://www.amazon.com/British-Forces-Motorcycles-1925-1945-Orchard/dp/0750970235/ref=sr_1_1?s=books&ie=UTF8&qid=1541713162&sr=1-1&keywords=british+military+motorcycle

email (option): cas.vanderwoude@gmail.com

To allow for the tank top Vokes filter pipe. Ron

email (option): ronpier@talk21.com

The 'cut off' petrol tanks were only fitted to the last three contracts of the war and the filters themselves only to the last two contracts...

It's worth noting therefore, that no Vokes filters were fitted to M20s during the desert campaign...There is a picture of an M20 in Italy with one fitted that was shown in a previous post on the subject but that must have been either a late war machine or a 'retro' fitment of the tank/filter assembly...

The large 'Deluxe' type tank fitted to early contracts was superseded by 1941 and possibly during 1940. I'm sure someone will clarify that date.

The 'mid war' tank was simply altered for the later contracts described above to accommodate the Vokes filter tube but was essentially the same tank.....Ian

email (option): ian@wright52.plus.com

Hello
could I ask you where did you get this important information?
I would like to know more about the tank and the filters, since I have a BSA with tanks cut and on which I would like to mount the filter and a friend of mine has a bsa of 43 with a big tank

thank you

email (option): bongiovanni1988@libero.it

According to O&M, the cutoff tanks were fitted from 1943? The filters had been in use throughout the war, so I guess they could have been added when required. Ron

During the latter half of 1943 the girder-fork steering-damper was removed from all new machines, the crankcase sump-shield was redesigned to become a pressed steel item incorporating additional protection at the sides for both the engine and frame-rails, and the fuel tank was altered by having the rear offside corner removed to accommodate the substantial hose section leading from the tank-top mounted Universal War Department pattern Vokes air filter to the carburetor air intake. This last modification was carried out on a large proportion of machines destined for service in hot, dusty climates. By early 1945 the Vokes filter was fitted as standard to the fuel tank of all new models irrespective of where they were destined to serve, the filter being secured to the tank by mounting-strips attached to the previously redundant knee-grip locating

email (option): ronpier@talk21.com

PS. See the info link that Cas posted. Ron

email (option): ronpier@talk21.com

For those new to the forum, you may not know the O&M that Ron referred to above. O&M refers to a book by Orchard and Madden and is titled "British Forces Motorcycles 1925-1945". It has been newly updated and is a great reference. One of many sources is at the link belwo ...

https://www.amazon.com/British-Forces-Motorcycles-1925-1945-Orchard/dp/0750970235

cheers, Scott D

['According to O&M, the cutoff tanks were fitted from 1943? The filters had been in use throughout the war, so I guess they could have been added when required.']

They were fitted to pre war (and early war?) Nortons I believe...However, to date there is no photographic evidence of them being fitted to M20s before or during the desert campaign, which would have been the case if they were readily available I would have thought...

In the photo of the prototype India Office M20 it has a Talflow filter fitted..(The type also fitted to the 1940/41 WB30 prototype) There is also a photo of an early WD M20 with the round, louvred 'canister' filter fitted next to the rear wheel...

Pictures of M20s in the desert show them with the filter fitted by the rear wheel, similar to the set up on the Norton in Riks post, and with improvised filter arrangements using large filters that appear to have been sourced from 4 wheeled vehicles..

Any evidence of the use of a Vokes filter at the time of the desert campaign would indeed be illuminating....

The BSA parts lists indicate they were only fitted as original fitment to the last two wartime contracts, with one further contract having the tank fitted but not the filter assembly...Those three contracts did run from late '43 onwards from memory...Ian

email (option): ian@wright52.plus.com

This is wonderful information! Thank you.
Several have mentioned that the last three contracts of M20 production used the tank with the indent on the right rear of the fuel tank. Can you list what these contract numbers are?
My WD M20 Serial Number: 103026 was produced during contract S2603 (March 1943 - July 1944). It should have the tank with that indent?

email (option): questmasters(at)hotmail(dot)com

The 'non cut off' petrol tank is part no. 66-8246...The 'cut off' tank is part no. 66-8211...

Contract number S2603 (8000 machines) was fitted with the later 'cut off' type tank but no air filter....

The following contracts, S5209 and S7218, were also fitted with the 'universal air cleaner' (parts list description)....

There are in fact other contracts but only for quantities of machines from approx. 1-20 in number rather than the more substantial quantities of the contracts noted, so I have ignored these...Ian

email (option): ian@wright52.plus.com

The last three contracts would have been "Catalogue Refs" 35,36 & 37 - S2603, S5209 & S7218 respectively.

As Ian indicates, this suggests production dates from late 1943 onwards. S2603 was scheduled for production at 2400 per month commencing December 1943.

In any photograph of motorcycle and rider, the fuel tank cutaway area is usually obscured. We are fortunate though, with S2603 commencing at C5207518 that this well-known image at least lets us see most of the serial number - C52075** - and the cutaway section. It will be somewhere between WM20 96818 and WM20 96899. Almost definitely a December 1943 build.



I would say that it's most unlikely there is a tank-top filter - they can't improve the sleeping potential.

Thank you so much for the education! This is fantastic to learn about!!! Got it, my motorcycle should have the fuel tank cut-away section.

And since I am just learning, I am a bit confused. I thought contract S2603 was from March 1943 to July 1944 for 8000 motorcycles. I own WM20 103026, which I was told was the 6209th bike of 8000 from contract S2603. Now I am reading that contract S2603 started in December 1943 with a scheduled production of approximately 2400 per month? Would that mean my M20 was made in roughly February 1944?

email (option): questmasters(at)hotmail(dot)com

There is always a certain amount of intuition and guesswork in interpreting these records as what remains is incomplete and in the pre-computer age, there was less consistency in record-keeping than we might expect.

The contract prior to S2603 (S1048 Catalogue Ref. 34) was dated 24/9/1942 and was for 15000 machines to be delivered from May 1943 at 2000 per month. It looks as they were then on target to complete it by December to allow the commencement of S2603. The subsequent contract S5209 was scheduled at 2000 per month from July 1944...so it would seem reasonable to assume that the 8000 of S2603 were spread over the six or seven months from December '43 to July '44...more like 1000 per month. It may well be that a shortage of materials caused the delay.

I would feel confident in saying 'The first half of 1940' but probably not more specific than that. Working backwards would suggest around May 1944.

This is so fascinating!!!!
I have put some of this information on the website for my M20, and will happily correct it with these details!
Like most M20 owners, I am trying to find out the history of this specific motorcycle so I can restore it correctly, especially if I can establish the exact unit it was assigned to during WWII. I've now seen several M20's of very close registration numbers assigned to the 1st Polish Armored Division.

I will continue to search and ask questions on this forum, thank you so much for the help!!!!😊

email (option): questmasters(at)hotmail(dot)com

There was no system behind how individual machines were allocated and as you've seen on the post-war records, units were pencilled-in and then erased. All that can be said is that it ended its service life at a BAOR (British Army Of the Rhine) depot in 1969.

It's not unusual to find traces of vehicles with similar numbers spread out all over the world.

Based on production dates, it's unlikely that yours went to France in June 1944 but it could easily have been issued as a replacement to any of the British or Allied units forming 21st Army Group....but you can't exclude that it arrived in Germany with a unit transferred there from somewhere else, such as Italy...or it may never have gone abroad in wartime and have arrived at BAOR during the 1950s. They kept large stocks for issue to Territorial units on cold-war exercises etc.

12 Heavy Workshop REME who rebuilt your engine were in the old Hanomag truck factory at Hannover.

I found this quote on a BAOR forum -

"I have just remembered a major unit in Hannover in 51,there weren't many,none of the arms, all adm etc.Actually there were two,15 RSD RAOC at Vinnhorst,last stop on the 18 tram line. 12 Heavy Workshop REME occupied the Hanomag Truck factory at Hannover-Linden,at the back of the factory was what appeared to be a cleared bomb site,thr rubble had been used to form the banking for an arena and they had laid down a cinder speedway track.I went there one Sunday afternoon,the riders were servicemen and German civilian employees,they rode what looked like modified,(cannibalised),army bikes that were quite good performance wise.The crowd was mixed so when a German won the locals really kicked up their heels,can't blame them they didn't have much to cheer about,and when the occupiers got beaten it was time to celebrate.Never went there again,I was posted to Bielefeld the following week."

Maybe you should build a stripped-down M20 and race it !

Thank you everyone! I have updated the page with this new information and will continue to build and correct it as I restore and learn about my M20!
http://www.questmasters.us/1944_BSA_M20.html

email (option): questmasters(at)hotmail(dot)com

Were there different styles of gas caps used throughout 1939-1945 M20 production. And if so, what is correct for a 1944?

email (option): questmasters(at)hotmail(dot)com