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#34268 - 02/04/08 12:38 pm BSA M20 Gearbox Help Request  
Joined: Aug 2001
Posts: 3,913
Britbodger R.I.P. Offline
In Remembrance
Britbodger R.I.P.  Offline
In Remembrance

Joined: Aug 2001
Posts: 3,913
Houston Texas
A friend of mine's (yes - I does has friends RicB :p )M20 is sitting dormant because of gearbox problems. He would love to get it back on the road so I said would ask the BSA experts who resides on this board.

Unfortunately don't know the specifics of the problem but, for starters anyway, wondered whether the M20 shares the same gearbox internals as other Beeza's.

Any help/advice would be much appreciated.

Thanks in advance

beerchug

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#34269 - 02/04/08 1:27 pm Re: BSA M20 Gearbox Help Request  
Joined: Aug 2001
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Zimm Offline
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Zimm  Offline
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Joined: Aug 2001
Posts: 276
The land of pleasant living
Bodger:

Before he gets too deep into the box, make sure the clutch is spot on, unless absolutely sure the problem is in the box. Mine will fail to downshift if the clutch isn't right.

Getting it right includes making sure there is full movement of the clutch rod. Little stuff like the lower adjustment matters. Mine had wear in the clutch lever fulcrum point. Once I made a little bushing and installed it, it worked a lot better.

Zimm

#34270 - 02/04/08 1:41 pm Re: BSA M20 Gearbox Help Request  
Joined: Sep 2002
Posts: 7,811
Alex Offline
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Alex  Offline

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Posts: 7,811
Seattle
Malcom, while the M20 box is very similar to the B31/B33/A/A10 box, the internals do not interchange. Still, M20 boxes and spares are not exactly rare, having been used on the vast quantities of WM20 as well as M33's, M21's and not quite as common M23&24.

Nice thing, though, they are dead-*** simple and very rugged in all areas except perhaps the cases, which seem to get broken a lot.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#34271 - 02/04/08 2:14 pm Re: BSA M20 Gearbox Help Request  
Joined: Aug 2001
Posts: 3,913
Britbodger R.I.P. Offline
In Remembrance
Britbodger R.I.P.  Offline
In Remembrance

Joined: Aug 2001
Posts: 3,913
Houston Texas
Thanks Zimm, but think his problems go deeper than the clutch.

And thanks for the info on the internals Alex. Now I'll start looking for source of parts once I find out what he needs.

BTW, he is a local flattracker and has a really nice Trackmaster BSA twin (amongst his huge collection of British and other bikes) that he races from time to time. Will try and post a photo when I get home.

beerchug

#34272 - 02/04/08 3:34 pm Re: BSA M20 Gearbox Help Request  
Joined: Sep 2002
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Alex Offline
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Alex  Offline

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Posts: 7,811
Seattle
Oooh, yea. Bodger, Domiracer will prolly have everything you need. If they don't, Draganfly certainly will.

Mmmm, trackmster.

Cheers.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#34273 - 02/04/08 5:04 pm Re: BSA M20 Gearbox Help Request  
Joined: Aug 2001
Posts: 157
Pat Offline
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Pat  Offline
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Joined: Aug 2001
Posts: 157
I have a spare BSA 4speed trany, casting no. AM 65-3394. One of the guru's will tell us if it's an M20 one.

#34274 - 02/04/08 5:23 pm Re: BSA M20 Gearbox Help Request  
Joined: Aug 2001
Posts: 3,913
Britbodger R.I.P. Offline
In Remembrance
Britbodger R.I.P.  Offline
In Remembrance

Joined: Aug 2001
Posts: 3,913
Houston Texas
Thanks Alex and Pat for the additional info bigt .

Pat,

Any idea what you want for the gearbox if it is the correct one?

P.S. Hope to see Dave Valden (the guy with the M20) this weekend and will pass on the info.

#34275 - 02/05/08 3:45 pm Re: BSA M20 Gearbox Help Request  
Joined: Aug 2001
Posts: 157
Pat Offline
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Pat  Offline
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Joined: Aug 2001
Posts: 157
I'd like $80 plus shipping for the tranny. First gears are worn but everything else is good. Comes with the clutch, worn but the plates are there.

#34276 - 02/05/08 6:44 pm Re: BSA M20 Gearbox Help Request  
Joined: Sep 2002
Posts: 7,811
Alex Offline
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Alex  Offline

BritBike Forum member

Joined: Sep 2002
Posts: 7,811
Seattle
Pat, you can identify the box by the fact that the clutch actuation lever is attached to the center of the outside cover on M-20 gearboxes. Somewhere around the end of the war they changed the lever to rotating a shaft coming in the top center of the cover inside a banjo-shaped smaller casting. This later type was also used on rigid and plunger B-series bikes. Later B and A-series boxes have a rotating shaft coming directly into the top of the cover near its joining face with the inner cover.

And speaking of which, I forgot about the plunger and rigid B-series, which used essentially the same box as the M-20 but with different ratios. Many parts from one of those boxes could interchange...but the gears themselves are different.

Cheers.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#34277 - 02/05/08 7:25 pm Re: BSA M20 Gearbox Help Request  
Joined: Aug 2001
Posts: 157
Pat Offline
BritBike Forum member
Pat  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 157
Thanks Alex. Had to go look at pics to check your meaning but see that my tranny is the later type with the clutch arm on the top of the side cover. There is a no.8 stamped on the tranny case, top left side above the sprocket, does this give any indication as to model, ratio, etc? Won't fit my C10 anyhow!


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