Help: BSA MODEL IDENTIFY!!

[mauricio]

Hi!
I´ve got this BSA bike. I would like to know which model it is because I want to restore it.


ENGINE: BB33-8138

FRAME: ? ? ? ? ? ? I can't see it.
The number must be secret under the thick(bulky) painting. In what zone of the frame is normally located ?

Thanks a lot

[Bruce]

The B33 is a 500cc bike and that is the model name the B31 was the 350cc version.I would expect to find the frame number around the steering head area.Happy hunting.

[fidobsa]

It looks like a B33 engine in an ex army M20 frame but I could be wrong. There was a model called the M33 but I think they were only made with plunger frame and telescopic forks, based on the M21 rolling chassis.

[L.A.B.]

It looks like a B33 engine in an ex army M20 frame but I could be wrong. There was a model called the M33 but I think they were only made with plunger frame and telescopic forks, based on the M21 rolling chassis.

Apparently there was an early M33 rigid version made from 1948-55 which was basically an M21 series cycle with a B engine, although M20/M21/M33 production from late 1948 had telescopic forks.
However, an M33 engine should have a BM33 prefix, this BB33 prefix and 8138 number would seem to date the engine to the 1956 production year, so it is likely that the engine and/or frame does not match the forks.

The frame number of these rigid M/B series cycles should have an ?M20 prefix, and should be "...found stamped on the seat or the head tube lug..." .

[douglas]

i wouldn't restore it. i'd put a chainguard, knee grips and some transfers and ride it!!!  douglas

[Goldy]

Yes excellent idea. There is too much over restoration. I would re wire it as well.

[ojcdrc]

The engine as stated is from the fifties, the frame is from a 37 to 39 M series and the frame number can be found on the lug on the front down tube near the engine plate. Only 37, 38 and some 39 models had this type of oil tank mounting. The  frame number will start with the prefix H, J or KJM19. the original engine would have been an OHV, if it was side valve ie M20 or 21 it would be a hand change gearbox. Hope this information helps    

[fidobsa]

That's interesting. So it could have started life  as an Empire Star perhaps?

[ojcdrc]

Yes, it could have started as an Empire star. This frame was used for the M19 350. (While generally in this era the 350 light weights were designated B series there were 350 engines used in the heavy weight frame). the other two models were the 500 sports (M22) and Empire Star (M23) all had the frame number prefix M19.
The Empire Star had a 20 inch front wheel while the others had a 19 inch wheel this bike looks as though  the wheel is a 19", assuming it is the original front wheel.
  

[douglas]

  as the wm20 girders were famous for cracking the front tubes i'm curious to know if that was unique to the war models ie cheaper steel or were pre-war girders hardier?? douglas