The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: 63a10r on 24.09. 2006 22:39
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what is the casting # on a "thick flange barrel?"
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Hi there... Just been out and had a look at mine and the number is 67-1210 these barrels as far as I know are 1961s but of course they may not be originals.
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Hello, 67-1210 from 1954 a10r, 67-1074 1954-58 a10's. From 1958, 67-1210 for all a10's.
1\2 in base on thick flange block (Bacon's twin restoration).
I've read somewhere about high comp pistons fitted to thin flange 67-253 blocks resulting in the whole top wanting to fly trough the tank...
Regards'
E.
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I have gone down the path of 10.5 :1 pistons in thin flange barrels on my '55 Flash. The barrel broke off above the flange within 10 miles! I have also broken thick flange barrels with 8.75:1 pistons, but they had been resleeved.
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During the 1950's, as the years progressed and the A10 engines were developing more and more power, barrels were regularly breaking away from their flanges so BSA produced the "Thick Flange Barrel" in the hope that it would cure the problem. I think that it probably did when they were sort of new but now, as these barrels are at least 45 years old, they could be suffering from metal fatigue and obviously won't be as strong as they were.
My A10GF is running on a thick flange barrel but I decided to fit low compression pistons in the hope that I would achieve more reliability. I don't think it makes that much difference to the general running of the bike. It cruises comfortably at 65mph even 2-up and loaded up with camping gear. And it hasn't given me any trouble for the 6 years it has been on the road, attending four continental rallies, several British National Rallies and club camps.
However, I will post an interesting story shortly about preparing it for the Danish BSAOC International Rally in 2005. Worth waiting for?? We'll see and let you be the judge!! ;) Beezageezauk.
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The main problem occurring with barrells now is when they are resleeved there is not much original metal left above the flange, even thick flange types. Stepping the sleeves and brazing top and bottom seems to keep them together. I have had thick flange barrells break with 8.75:1 pistons but with above method of resleeving I have had no problems.