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BSA m20 rigid frame exploded view source? #292221
01/04/10 4:15 pm
01/04/10 4:15 pm
Joined: Aug 2005
Posts: 99
UK
M
maxwell Offline OP
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maxwell  Offline OP
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Joined: Aug 2005
Posts: 99
UK
Hi there
I have just aqquired a BSA M20 frame, it is rigid
and has BM20 on the number. It has sidecar lugs on it also.

I recieved 2 gearbox mount plates with the frame but I am not sure weather I have the correct ones.

Is there a good exploded view or pictures of all the gubbins needed to mount the engine / gearbox (spacers adjusters etc)
I found one for the wdm20 frame but I am not sure weather the earlier and later models are the same.

I can post pics of these plates I recieved as soon as I have the camera working.

Thanks for any help

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Re: BSA m20 rigid frame exploded view source? [Re: maxwell] #292293
01/04/10 9:09 pm
01/04/10 9:09 pm
Joined: May 2004
Posts: 3,696
Sydney Australia
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BSA_WM20 Offline
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Joined: May 2004
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Sydney Australia
They are the same.
The M20 used 2 different gear boxes but all of them were built up into the prewar shell which has both mounting lugs under the box.
You will find this a very helpful site<http://members.quicknet.nl/ahum/>


Bike Beesa
Trevor
Re: BSA m20 rigid frame exploded view source? [Re: BSA_WM20] #292315
01/04/10 11:18 pm
01/04/10 11:18 pm
Joined: Aug 2005
Posts: 99
UK
M
maxwell Offline OP
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maxwell  Offline OP
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Joined: Aug 2005
Posts: 99
UK




Thanks for the reply, I have looked at the m20 site there. I have a later model, I am glad to hear they are all the same ha ha.
Is there no difference in the plunger gearbox mount plates? I grabbed the plates from a pile wich contained a plunger m20 and b31 plunger frame also, so it was a bit of a guess.

See the pictures, the bottom plate in the top pic has a curve along the lower edge. What is that for?
Also both of them have that bracket piece sticking out. I assume its for gearbox adjuster, but should it be on both sides?
Also is the additional metal stud for the stand spring?
Thanks for any help, cheers

Re: BSA m20 rigid frame exploded view source? [Re: maxwell] #292376
01/05/10 11:44 am
01/05/10 11:44 am
Joined: May 2004
Posts: 3,696
Sydney Australia
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BSA_WM20 Offline
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Rigid M20 / 21 frames are all the same with respect to the gear box & mounting plates.
There was only one "engine rear yoke plate" for rigid M20 & M21 part number 66-4157 from 1936 through to 1958.
Rigid frame plates are identical.
Plunger frame plates are handed.
The bottom of a rigid plate is flat, like the top plate in your photo
The bottom of the plunger is curved, like the bottom one in your photo.
So it is back for a second try at the lucky dip bin for you .
OTOH if the slots & holes line up I suppose you could cut of the extranious bits.
There is only one chain adjuster on the right side of the bike under the oil tank.
You could not get to it on the left side as it would be behind the primary and under the drive chain.

And to be fair you did not mention anything about plungers in your original post.
Plunger frames are different from rigid frames.
Rigid frames are all the same at the back but have different front down tubes.
Long ones for girders.
Short ones for teles.
Note BSA made a tele conversion for girder forked bikes which consisted of , naturally the actual forks & guard but also a modified top clamp plate which is slightly off set to throw the forks slightly foreward so that the mudguard clears the frame under compression.


Bike Beesa
Trevor
Re: BSA m20 rigid frame exploded view source? [Re: BSA_WM20] #292387
01/05/10 1:14 pm
01/05/10 1:14 pm
Joined: Aug 2005
Posts: 99
UK
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maxwell Offline OP
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maxwell  Offline OP
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UK
Hi there
Thanks for the reply, That seems to answer my question. I have 1 plunger and one rigid plate.
My front half has the shorter downtube for the telescopic forks.
Cheers.
Back to the pile

Re: BSA m20 rigid frame exploded view source? [Re: maxwell] #292500
01/05/10 10:40 pm
01/05/10 10:40 pm
Joined: Aug 2005
Posts: 99
UK
M
maxwell Offline OP
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maxwell  Offline OP
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Joined: Aug 2005
Posts: 99
UK
Oh yes the holes and slots do all line up.
I may as well just use it.
cheers


Moderated by  Allan Gill, Jon W. Whitley 


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