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#315946 - 05/29/10 10:01 pm M20 questions  
Joined: Aug 2008
Posts: 1,429
Jim Hultman Offline
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Jim Hultman  Offline
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Joined: Aug 2008
Posts: 1,429
Minnesota, US
I'm trying to bring an M20 of uncertain year back to life. The bike was sold to me many years ago as a 1939, but it is titled as a 1954. The reason for this is the plate on the engine, which gives the engine number and is dated in 1954:



Here's shot of the whole bike:



The problem with the year is that all the parts books and manuals I have for M20's are evidently for the later bikes. The reason this is a problem is that although I am making progress and even have the magdyno giving spark, the transmission is stuck between 3rd and 4th (according to the little disk indicator on the tranny). And all the references I have for tranny's show a very different version.



Also, would these bikes have had matching numbers back then? The engine number is 121539 on both the engine case and the plate, with a very light WM20 underneath. The frame is marked WM20 121455.

From the references I have, that would put it as around 1944, which does make some sense, because the other M20 I have is titled as a 1944 and has the same tranny.

I'd appreciate any thoughts or comments and perhaps a clue as to where I might find a parts book for this tranny. I have Kim's CD and some other hard copy material, but the only one that gives any clue to this tranny is the 300 page 1939 "all models" list on the CD. Not much help there.

Thanks!

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#315991 - 05/30/10 4:41 am Re: M20 questions [Re: Jim Hultman]  
Joined: Jul 2001
Posts: 12,056
Lannis Online content
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Lannis  Online Content

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Posts: 12,056
Central Virginia
I'm finding the same sort of thing about my M21. The Kim CD indicates that the single-spring clutch was only used up till 1948, except for "AA" bikes. Mine's a '55 and has it, and I don't THINK it was an AA bike since it came from Oztrailia.

Lannis


OK, I admit it, I'm addicted to brake fluid.

But I can stop any time I want.
#316007 - 05/30/10 9:57 am Re: M20 questions [Re: Lannis]  
Joined: Dec 2004
Posts: 8,882
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,882
Scotland
Yours is an ex-army bike

http://en.wikipedia.org/wiki/Royal_Electrical_and_Mechanical_Engineers

As such during regular maintenance if an engine overhaul was needed they had a stock of pre reworked engines which were swapped so the bike could reenter service quickly. Its very rare for a Ex-Army bike to have the same numbers it left the factory with.

All the plate refers to is the year that engine was overhauled, and if the previous overhaul had been on the last rebore then they would have fitted a new barrel and took it back to Std bore.

So its very likely you have a bike from WW2 and if it is a 39 then its had a very interesting history, if only it could talk.

#316036 - 05/30/10 12:41 pm Re: M20 questions [Re: kommando]  
Joined: May 2004
Posts: 3,547
BSA_WM20 Online content
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BSA_WM20  Online Content
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Sydney Australia
Kommando has got it .
The plate is as stated an overhaul plate.
The usually quoted number of WM 20's made for the war effort is 126,000.
Mine is a 1943 military surplus and its matching numbers are 78096 so yours would have to be 44 on.

Number did match ex factory but the engines were removed and overhauled on the bench so it was hit & miss as to weather a particular engine went back into it's original frame and popular wisdom is matching numbers signifies a war surplus machine.
The overhaul plates are fairly rare and the WM20 nutters pay good money ( or parts) for them as most owners forked out the 2s & 6p for an alloy cover back when they were new.
Farmers otoh left the plates there so that they knew the condition of the engine so you very well could have a reconstructed bike from a frame and a motor from a pump/ saw etc,etc.

There are a lot of M20's down here.
The Australian army ran them till 1966 when they were replaced with the B40-GA's, till the spare parts ended up in the Suez and the Army then went to Honda Elsaonres for off road & Suzuki 400 twins for escort & general road use.
As late as 1991 brand new crated WM20's surfaced from government stores & I am sure that there are still more of them lurking in the dark forgotten corners.
Post WW II they went for around 10 ( $20 Aust ) as surplus which was 1/2 what a Villers stationary engine costs so a lot ended up in equipment .

As for literature.
BSA did not start printing "exploded" type parts books till around 1946 and even then it was 1949 before the new style books were available for all models.
Prior to that BSA printed one parts book that covered all models for that year and simply showed all of one type of part, so you got a whole page of crank shafts and another of con rods etc,etc.
Bill Green can supply you with a reproduction military spares list which has sort of semi exploded views in it.
With the exception of moving the crank case breather, I do not think that there are any engine differences between the WD & 1949 M20's so you can use the latter book for assembly details.


Bike Beesa
Trevor
#316060 - 05/30/10 2:09 pm Re: M20 questions [Re: BSA_WM20]  
Joined: Aug 2008
Posts: 1,429
Jim Hultman Offline
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Jim Hultman  Offline
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Joined: Aug 2008
Posts: 1,429
Minnesota, US
Really appreciate the help, guys. I do have one additional question:

Can the tranny outer cover be removed without taking the tranny out of the bike? Some of the documentation I've been able to find suggests that to do anything to the tranny, it must be removed from the bike. I suspect the shifter problem could be solved by just pulling the cover, if it's like most others I've worked on.

Also, I have found one amazing piece of information about this bike. I posted my questions on the WD Motorcycle forum, and here's one of the answers I got back from Henk:

Quote:
Your bike is from the last contract (S7218) and is build in late 1945, it seems that the last bikes of this contract could even have been build in very early 1946, I am not sure about that. The post war military registration number was 42YD01, during the war it had tank number C5890555. It was used in Germany after the war at BAOR and was sold by the military 16-02-1970.

Your bike would have been fully equipped with pannier bags, Vokes filter etc. when new. Here a picture of such a bike from a slightly earlier period.


I now have the ORIGINAL WWII tank numbers as well as the post war registration numbers!!Amazing!!

#316107 - 05/30/10 7:44 pm Re: M20 questions [Re: Jim Hultman]  
Joined: May 2004
Posts: 3,547
BSA_WM20 Online content
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BSA_WM20  Online Content
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Sydney Australia
Inner and outer can be removed in situ but getting to the nuts behind can be a bit of a contortionist to do so.
Also the thickness of both gaskets is important.
Use the kickstart to pull the cover off.


Bike Beesa
Trevor
#316123 - 05/30/10 9:21 pm Re: M20 questions [Re: BSA_WM20]  
Joined: Aug 2008
Posts: 1,429
Jim Hultman Offline
BritBike Forum member
Jim Hultman  Offline
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Joined: Aug 2008
Posts: 1,429
Minnesota, US
Originally Posted By: BSA_WM20
Inner and outer can be removed in situ but getting to the nuts behind can be a bit of a contortionist to do so.
Also the thickness of both gaskets is important.
Use the kickstart to pull the cover off.

Thanks Trevor

I assume then that the entire shifter shaft and mechanism stays with the tranny? Also, I know I have to remove one of the circlips on the shifter shaft, but do you need to take both of them off?

#316137 - 05/30/10 11:33 pm Re: M20 questions [Re: Jim Hultman]  
Joined: May 2004
Posts: 3,547
BSA_WM20 Online content
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BSA_WM20  Online Content
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Sydney Australia
Yep, the selector should stay within the inner cover.
It is held in there by a plain wire circlip.
However the one that holds the indicator to the shaft will have to be removed .
If the inner one is missing you must replace it and Russel Motors in the UK seem to be the only retail source of these plain wire clips.
I rather feel that yours will be missing.
This allows the ratchet pauls to slide backward just enough to drop off the ratchet plate then you either are stuck in 1 gear or can only change between a single pair of gears.
Be very careful with the main shaft as it dose not have any retaining mechanism.
The latter model of this gearbox has a retainer behind the left side bearing but the "jelly bean" boxes do not and if the main shaft moves just a little the kick start ratchet can not disengage or just jambs.

This should also be in mind when you work on the clutch.
Pounding on the other end of the main trying to get the clutch hub off will also cause the shaft to shift


Bike Beesa
Trevor
#316140 - 05/30/10 11:40 pm Re: M20 questions [Re: Jim Hultman]  
Joined: Aug 2008
Posts: 1,429
Jim Hultman Offline
BritBike Forum member
Jim Hultman  Offline
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Posts: 1,429
Minnesota, US
This is interesting. Got the cover off with no problems. The nuts behind the case are a bit of a hassle, but nothing serious. But when I got it off, this is what I was greeted with.....



On the bright side, I did mange to get the shifter mechanism freed up with a little coaxing. And it seems all the gears are there. The down side is what's in the tranny case. Not oil. Not Hypoid 90W. But pure grease. I have no idea how they got it in there, and I have even less of an idea of how I'm going to get that stuff out of there. Fill it with some light weight oil and run it until it's hot? Then HOPE it thins out enough to drain?

Is that normal for these bikes? If so, they should have a grease zerk instead of a filler hole!

Also, Trevor, as you can see, the gasket was toast even before I got to it, and I don't have a replacement on hand. I guess I'll have to make one. You said the thickness was critical?
Any idea what thickness of gasket stock I'll need to find?

Appreciate the tips on the circlips!

Jim

#316180 - 05/31/10 8:53 am Re: M20 questions [Re: Jim Hultman]  
Joined: Sep 2006
Posts: 144
LJ. Offline
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LJ.  Offline
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Posts: 144
Peterborough. UK
lol... What a mess eh? but relax Jim it is normal. Often oil and grease were mixed 50/50. I have not yet tried that formula as I run a straight 50 grade in the box. I would think that a stiffer oil or oil/grease would help in engaging gears but certainly I have found that it is a disadvantage in colder weather. It does help to prevent oil leaks though! lol It's a little while since I opened up my gearbox so I'm a little rusty on advice but take a peep at my webpage, it might be of use to you.
M20/21 Gearbox page!

P.S. Having read through that page again... I found that I only had to replace the gear clutch dogs. But if your having problems with a 'stuck' third fourth gear then sounds like a different problem in which case you'll be needing to look in the inspection hole, with mirrors and good torch you should be able to manage.


LJ.
*******
1940 BSA M20 500cc Girder/Rigid- In Bits!
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7 500cc Girder/Plunger Star Twin-Black
1953 BSA B33 500cc Teles/Plunger-Maroon
1961 BSA A10 650cc Golden Flash-Blue
1961 BSA A10 650cc Golden Flash-Red
#316205 - 05/31/10 12:08 pm Re: M20 questions [Re: LJ.]  
Joined: Aug 2008
Posts: 1,429
Jim Hultman Offline
BritBike Forum member
Jim Hultman  Offline
BritBike Forum member

Joined: Aug 2008
Posts: 1,429
Minnesota, US
Thanks LJ. Great pictures on your web site! I do have the inspection cover off, but I find that the gears are so plugged up with grease that it's hard to see anything. If I was to do this right, I suppose I should take the box out and rebuild it, but now that the shifter seems to be functioning as it should, I think I'll just button it up and see how it works first.

Still got a lot to do to get the bike on the road!

Appreciate the help!

Jim

#316206 - 05/31/10 12:13 pm Re: M20 questions [Re: Lannis]  
Joined: Aug 2008
Posts: 1,429
Jim Hultman Offline
BritBike Forum member
Jim Hultman  Offline
BritBike Forum member

Joined: Aug 2008
Posts: 1,429
Minnesota, US
Originally Posted By: Lannis
I'm finding the same sort of thing about my M21. The Kim CD indicates that the single-spring clutch was only used up till 1948, except for "AA" bikes. Mine's a '55 and has it, and I don't THINK it was an AA bike since it came from Oztrailia.


Hey Lannis. Can you explain the "AA" bike? These bikes seem to have a lot of intersting details about them, and I haven't heard that term before.

Jim

#316208 - 05/31/10 12:29 pm Re: M20 questions [Re: Jim Hultman]  
Joined: Sep 2006
Posts: 144
LJ. Offline
BritBike Forum member
LJ.  Offline
BritBike Forum member

Joined: Sep 2006
Posts: 144
Peterborough. UK
Your welcome Jim... and I bet your gonna find a single spring clutch too! But I understand they are also a good clutch like the six spring job, just its that much more difficult to fit and remove.

To beat Lannis explaining 'AA' This is the acronym for Automobile Association, a breakdown service in the UK.

Automobile Association


LJ.
*******
1940 BSA M20 500cc Girder/Rigid- In Bits!
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7 500cc Girder/Plunger Star Twin-Black
1953 BSA B33 500cc Teles/Plunger-Maroon
1961 BSA A10 650cc Golden Flash-Blue
1961 BSA A10 650cc Golden Flash-Red

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