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I originally posted this back in 2017 on the "British bikes in general" forum where it never generated any replies, so I'm reposting it here here. Hope that's OK.

Back in 2012 I bought the machine shown in the pictures. It's a one-off racer with an BSA A50 power unit. It was used in the IoM TT and in various guises (e.g. 750 engine) on UK short circuit racing back in the '70s.

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I am a bit of a BSA nut (understatement), especially where their twins are concerned. The vendor, a guy in Didcot, Oxfordshire, UK told me it was built as a one-off racer by one Matthew Mason of Gannet Racing in the 1970s, starting off as a 750 and later on becoming a 500. The machine spent most of its life as a racer and was reportedly raced on quite a few UK circuits. It has some IoM history: 1986 MGP newcomers, rider Chris J Smith, 83.89mph; 1988 MGP, same rider, 85.33mph; 1989 MGP, same rider, DNF.

Some details on the bike, it has a hand built double loop frame, a la Manx. Box section swinging arm, modified Armstrong front forks, one off all alloy fuel and oil tanks. Modified TZ front wheel and TZ disc and a modified Rickman rear wheel and disc. The gearbox has a 5 speed Quaife cluster. The engine has end fed crank, rebalanced crank, 32mm inlet ports. The bike came to me with quite a collection of racing spares, such as sprockets, stands etc. Although I am very used to bikes with clip-ons, this machine has the most stretched out riding position I have ever encountered.

When I bought the bike, I met Matthew Mason briefly. He was then clearly an ill man. The person I bought it off had road-registered it and I bought it in good part for possible use in parades etc. Most recently my health has declined very severely and I never realised this ambition.

I have discovered that in their day Gannet raced a succession of bikes, including a B50, and that Mat Mason had a name as a very competent motorcycle engineer, but at about that point my knowledge ends. The Gannet Racing sticker that I have gives their phone number as Didcot 814406.

This bike is a little piece of history.

Can anyone recollect any history on Gannet Racing and this bike? Are there people, possibly close to the team, who are still around and that I could speak with? Is their rider, Chris Smith, still around? Does anyone recognise this bike and can they tell me anything of its history? I should be so pleased to know.

Any snippets of information will be gratefully accepted!

Thanks,

Jon

Last edited by JonnyD; 09/10/21 11:03 am.
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There is a lot of ingenuity in that. It's a wild looking thing, is it registered still and do you ride it? A 500 seems an odd size for these engines. I've never seen an A50 in Australia. They are mostly A65s.

Do you know if it's a short stroke version? Peter Crawford has a book coming out any day now with a history of the competition bikes based on A50 and A65s probably A70s. They had the A50 making very peaky power curves. It would be interesting to see what people did with the 500. I think they tried using A65 bore and shortening the stroke. Which would make sense. But unless you were tubbing that chamber you would need to fill it with piston crown to get high compression. And that could interfere with breathing.


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Originally Posted by Mark Parker
There is a lot of ingenuity in that. It's a wild looking thing, is it registered still and do you ride it? A 500 seems an odd size for these engines. I've never seen an A50 in Australia. They are mostly A65s.

Do you know if it's a short stroke version? Peter Crawford has a book coming out any day now with a history of the competition bikes based on A50 and A65s probably A70s. They had the A50 making very peaky power curves. It would be interesting to see what people did with the 500. I think they tried using A65 bore and shortening the stroke. Which would make sense. But unless you were tubbing that chamber you would need to fill it with piston crown to get high compression. And that could interfere with breathing.


The factory had several A50 Daytona's, AIUI between the years of 66-68, the frames for each year as I recall differed from the year before, some looking more Rickman esque and the others looking more like a modified factory frame. The 500 engines would have had magnesium cases if I remember rightly, cranks and bores were standard (though I am led to beleive they used Omega pistons). The head was ported to 32mm and used Spitfire spec GP carbs.

Daytona rebuild website.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
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Great article Allen. I'm sure they tested a short stroke. It's pretty tempting as the A65 bore could be used. Qualifying at 133mph is interesting. Magnesium casing and Iron cylinder I expect? I wonder how the weight saving compared to all aluminium. Plenty of space for a liner even at A65 bore size if they went there. Daytona is production so std bore and stroke required.

http://victorylibrary.com/brit/BSA-c.htm

So std is 65.5x74 using A65 bore 75x56.5mm. I know what I'd prefer. Then there's the big big bore version? I don't know, 744cc seems the obvious size for these, but the category is 500cc ohv. It would have been fun working on this stuff.


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I did consider making a short stroke 500 like you suggest, then I looked at how much billet cranks were then dropped the idea. You could make an A7 bore and stroke A50 with an A7 crank… but then what would the point be (66mm stroke I think?)

The magnesium castings could have been an old wives tale, but that is what I was told at the time. They did have a cast barrel so it would make you wonder why go magnesium on the cases?

A spitfire cam in an A50 makes for a bike that really shifts. Making a tuned one with a full race SRM cam would be really interesting.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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A7 stroke is 72.6 mm, bore 66 mm. Stroke of A50/ 65 is 74 mm.


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