NotSure > wrote:

<snip>
>
> I am stumped.

OK, I'm not sure it's a twin, actually. That appears to be a single
downtube frame, and the visible cylinder is mounted right behind it, on
the centre line. The finning on the right-hand "cylinder" does not go
down so far. It may be something else - not a cylinder.

Vertical twins were incredibly rare pre-war. There was Triumph and....
what else?

It's much much more likely to be a single.

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Try Googling before asking a damn silly question.
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