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BSA Owners' Club Workshop Discussions

The BSA Workshop => Singles => Topic started by: watts on 28 Jan, 2025, 06:57

Title: M and B Plunger Frames
Post by: watts on 28 Jan, 2025, 06:57
I wonder can anyone help?

Were M and A/B series plunger frames the same.

I have a ZM frame (plunger) with a BB engine.

It will help find the extra bits I need.

I do wonder if they are but without sidecar frame mounts?

Thanks
Matthew
Title: Re: M and B Plunger Frames
Post by: Derek996 on 28 Jan, 2025, 09:44
No they are not the same. M series frame has a bottom rail that extends below the engine to the rear chain stay.
Title: Re: M and B Plunger Frames
Post by: Derek996 on 28 Jan, 2025, 11:34
I just found out how to add pictures.
Title: Re: M and B Plunger Frames
Post by: Rog1 on 28 Jan, 2025, 12:06
As a B33 engine will fit into an M frame, (see the M33) is it actually a matter of the right engine and gearbox plates, rather than the frame differences? I had a look in my parts books, and the engine/gearbox plates have different part numbers. So which, if any, plates do you have?
Title: Re: M and B Plunger Frames
Post by: idie on 28 Jan, 2025, 12:51
On the B31 frame the engine forms part of the frame which is of a lighter construction then the M type frame. The frame plates for both M and B frames are totally  different.
Title: Re: M and B Plunger Frames
Post by: watts on 29 Jan, 2025, 08:21
Thank you everyone.

My issue is cycle parts.

I need several bits some are shared (same part number) between M and B plungers have divergent part numbers but look very similar.  I need rear mudguard stays, looking at pictures the plunger part of frame appears to have the dimensions.

Thanks
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