year & model triumph (afaik)? from an old pix tia (identified as a BSA)

That’s a BSA B31 or B33.

Looks like a swinging arm model to me so I believe that dates it 1954-1960.
 

What is the difference between BSA B31 and B33?
Outwardly identical to the B31, the B33 featured a slightly larger carburetor, heavier flywheels and a larger rear tyre. The first B33s were built around rigid frames. But in 1949, plunger suspension became an option. Five years later, in 1954, swinging arm frames were introduced.

This one was in Sudbury On Canada, back in the 60s, mighta been a hardtail.

 
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from the above b31 wiki
The BSA B31 is a motorcycle that was produced by Birmingham Small Arms Company.

The BSA B31, introduced in 1945, was the first new model introduced by the company after the Second World War. Based on pre-war designs, it used a single cylinder four stroke engine that displaced 348 cc (21.2 cu in). Initially, it had a rigid frame and telescopic forks, the first use of such on a BSA. It developed about 17 bhp (13 kW), adequate for the roads of the day and enough to deliver a top speed of around 70 mph (110 km/h).There was a competition kit available for the original rigid model B31 and B33. It was immediately popular and was soon joined by a 500 cc (31 cu in) version, the BSA B33 and competition equivalents, the BSA B32 and BSA B34; the side-car versions, with stiffer suspension and different final demultiplication, were known as BB31 and BB33.

Plunger rear suspension was offered later, with a swingarm rear suspension frame available from 1954. The model continued in production until 1959, by which time the traditional Lucas magdyno had been replaced by an alternator and coil ignition.

The B series expanded through its life to include the famous BSA Gold Stars, and the bottom half of all engines has much in common with the M series side valve models. The M33, designed for sidecar work, combined the strong M series frame and the better-performing B33 500 cc overhead valve engine.



Looks like there isn't a separate b33 wiki, however

The 499cc "all iron" BSA B33 arrived in 1947. It was based upon the 1945 348cc B31 which was derived from the pre-WW2 OHV BSA pre-unit singles. Outwardly identical to the B31, the B33 featured a slightly larger carburettor, heavier flywheels and a larger rear tyre.
 
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Thisssissa B 31 Swing Arm ,

year & model  triumph (afaik)? from an old pix tia (identified as a BSA)


AND thississa PLUNGER FRAME 51 - 53 ish ? A 10 , frames essentially notta lot different between the twin & single .
BUT I think in YOUR picture , you can see the PLUNGER rear vertical spring arrangement . Notta bad olde cow , or bull .

year & model  triumph (afaik)? from an old pix tia (identified as a BSA)
Glareing at the OIL TANK might better decide .
 
checked out b33 google images, looking for that horizontal bracket, securing the rear fender to the top of the shock area, in the original pix

this looks like a very similar arrangement for year 57


looks like the swingarm setup, vs plunger & common to b31

53 plunger variant showing distinct rear fender attach diffs, from the original pix, & swingarm variants

for the plunger variant, the gap between the horizontal bracket & fender, is clearly much larger


close up original pix (might have to downsize to see, click on the minus option for sizing)


Anything distinct about the tank emblem? may narrow down a year,

i'll eventually link this thread to the bsa forum







 
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I believe the rear mudguard stay is as you have identified, signifying it as a swinging arm model.

That dates it between 54-60.

Your pic shows the bike has a mag dyno, so if your Google info is correct, that dates it at pre 59.

So that narrows it down to 54-58.

AFAIK there are no other changes of a nature that can be seen in your pic that will get you to a more precise date (the Brits weren’t big on ‘unnecessary’ change back then).

But you might wanna ask LAB to move this to the BSA forum and ask the BSA nerds…
 
yes pls LAB, move & amend as you see fit, prob easiest to link it over to bsa, then continue there
 
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