B33 frame ID

[Tomalandain]

Hello everyone, first time poster here so I'll apologise first if the etiquette is wrong.

I'm hoping someone far more in the know may be able to help me with what I'm lead to believe is a B33 swingarm frame. I will attach photos to this post which should hopefully help.

First off; VIN Number?? I have had a real good look over the bike and the only numbers that in my mind resemble anything close to a possible VIN are those stamped in to the casting for the engine bracket on the N/S down tube, please see pictured, there are numbers scattered around the bike, some I believe are casting numbers, others I'm not sure of... Is what is pictured on the down tube the VIN? Obviously goes without saying that there isn't a log book, but the reg is 878 ANO, unfortunately not live with the DVLA.

Secondly; as can be seen in the pictures, there are a number of things that I don't believe to be standard for a B33, such as the narrowing where the rear of the tank would sit, the infill plate where the passenger foot peg would be, and the bracket on the swing arm, so I'm after some really good pictures of how the frame should be, or even better BSA drawings of how it should be, so it can be brought back in line with a correct B33 frame.

Any help or advice would be phenomenally helpful as at the minute I'm at a bit lost with it.

Thank you in advance,
Tom

[Derek996]

The first picture of the headstock shows where the frame number should have been been but it has been mostly obliterated with welding and modifications that have been done to it. Looks like it had been CB???. CB31.---- would indicate a swinging arm from 1954-55. I have no idea what the numbers on the downtime indicate.
The narrowing in front of the seat may have been to fit a non standard tank and the infill on the footage loop could have been for a rearset footrest or maybe something else. Attached is a drawing for the 1954 B series and Gold star. The Goldstar has rear set mounting lugs in the passenger footrest loops but other wise is the same.

[idie]

I think there was a sidecar attached at some point. The plate with the hole in it for the fitting, maybe a ball joint. I had to do this on mine to attach a sidecar. I made a better job on mine. The two down tubes under the headstock may have broken at some point. The wrap round would have to be removed to repair. I had to do this years ago on a Super Rocket.

[JulianS]

The frame number should be stamped on the right side of the steering head tube - the opposite side to that shown in the first photo.
I think the number stamped on the front down tube lug is supposed to read as a CB31 prefix frame number though clearly not done at the BSA factory.

[Derek996]

I think there was a sidecar attached at some point. The plate with the hole in it for the fitting, maybe a ball joint. I had to do this on mine to attach a sidecar. I made a better job on mine. The two down tubes under the headstock may have broken at some point. The wrap round would have to be removed to repair. I had to do this years ago on a Super Rocket.

Yes! Sidecar mounting makes sense.