I am amused and somewhat gobsmacked that such a lowly engine as the 2.5 Silver Swallow has received so much attention! 4 pages no less!
Good grief, they are the epitome of poor engineering!
I've got 5 or 6 out in the shed that I stupidly said I'd sort for a friend.
They are unadulterated rubbish of the first order. [:@]
I won't say they are all like the ones Howard asked me to sort. The very early ones with the more rounded heads and non anodised cylinder jackets had reasonable fits. These were the ones that came in the very thick cardboard box of pastel green and white.
Even when this batch surfaced they sold here in Oz for about $30, very cheap! Even the first ones, the 2.5's had shaft problems.
The 1.5 cc engines on the other hand were good value and weren't at all bad.
The more modern anodised versions are horrors though. Poor fits from the start, but the cases have not been machined to the correct heights to ensure the correct exhaust and transfer timings. On pulling them apart I've found that the transfers on some barely open at bottom dead center so even if they feel good, there simply isn't enough transfer timing to get enough fuel into the combustion chamber to sustain running.
They'll run off a prime of course, but any attempt to get them to run from a tank won't achieve anything!
As I say, there must be some that are happy with them, I'd say they'd have to be the lucky ones
Life's too short to waste time on these things, well unless you're a masochist