Right then, this 1965 Lightning project, 'wot I been pestering you all about for a few years now, is about to get the twin head it should have had from the get go.
The twin carb head (Part No 68-0466) that came with the basket of other bits was quite badly damaged hence I bought another one (Part No 68-0701) recently.
However, now that I have Roy Bacon's 'BSA Twin Restoration' book (thanks for that Chaz), I can check what twin carb head I should have....
Or so I thought...
On looking in the book, my new twin carb head's part number (68-0701) does not feature.
The book shows that the correct 1966 twin carb head should be (68-0700).
(Incidentally it also shows that my original damaged twin carb head (68- 0466) should be 68-0465)
I don't really know how to ask this but is it possible that the fantastic book might have it, ever so slightly, wrong.....
Or am I being a bit of an eejit?
Feel free to say things like "How dare you".....
701 is a casting number, 700 is the head complete with fixed fittings (guides, studs).
Usual BSA numbering practice. Late A10 alloy head 67 1549 casting and part nuumber 67 1548.................
Thanks very much Julian...
Much appreciated,
Dave.
The 68-701 comes in a couple of varieties. Some 30mm some 28mm approximately. They generally have 40.5mm inlet valves.
It's worth checking what pistons you have; early ones look a bit like Triumph pistons as they do not have the deep valve pockets for the bigger valves. And mixing them can give clearance problems.
BSA also did specials, I bought one recently which I think was an early 40.5mm valve Spitfire head with the casting number blanked and 68-915 stamped next to it. They did the same numbering on a better ported '68 Spitfire.
I don't really know what they had in the 65 Lightning, BSA were doing quit a bit to tune the Lightning/clubman like 11-1 pistons and I'm not sure when they started with the bigger valves, what Mike Hailwood won on they pretty much brought out as the 66 Spitfire, minus rear sets and C/ratio gears though they were available. At least thatmodel can be geared well with the smaller rear sprocket.
Having ran (and still run) bigger valves on the small port head it makes zero difference to its performance, I've had much better performance from choosing the right cam and 928 carbs over any other setup and the standard 38mm valves. I did also make the ports smaller within the small port head.
All that aside, the correct head for 1965 would have been cast with the numbers 68-466