After going over to Bonneville last year with a Weslake V-twin bike (and having sold it), The question arose as to what we'd be taking next time - 2014.
At first we entertained using a blown Buell XB lump, but I couldn't get too fired up about it. Coals to Newcastle etc.
31st March was the 40th anniversary of me getting my first A10. So you can see how the train of thought went!
The options were to run in one of 4 classes; AVBG650, AVBF650, AVBG750 nad AVBF750. (A= special construction, ie. not a standard frame, V= vintage - pre '56, BG & BF mean blown gas & blown fuel) No records exist in any of these classes.
With almost no A10 stuff left in the workshop, we set about acquiring stuff. A trip to Newark netted a useable set of cases and other parts:
A trip down to London, and we bought a blank ally cylinder casting from Paul Grayson (discussed elsewhere). Topped, tailled & rough bored it:
Julian (of this parish) has kindly offered to supply cylinder barrel machining data, and has also helped out by supplying Muskrat with a clutch in exchange for his sending over a twin carb A7 ally head:
Profuse thanks to both of you.
You also see a Vauxhall Corsa turbo, which will provide the 'blown' part of the equation. £30 off ebay; just right for an engine of this size.
We all know how rare & expensive large-journal cranks are these days; the last one I saw went for about £300. So the decision to run in the 750 class was made for us when Baz from Harlow came up with a Norton crank from a 750 commando for £50.
Of course it needs a bit of lathe work to to accept BSA timing gear & oilpump drive. Also, an extension piece had to be pressed on to get the full width for the main bearing. Oilpump drive is LH thread, so had to screwcut the thread upside-down.
Obviously, we're using the INA needle roller timing side main. Carefully set the cases up in the mill. Found the main bearing bores out of line by .008"
Bolted the drive side half on and made a light cut in the drive side seal bore:
Used this to centre up when setting up the drive side case to bore out to take a Norton superblend main bearing - 10mm bigger than stock BSA:
To complete the timing side case work, oilways have to be added to supply the end-feed to the crank. This is often done via the bottom timing cover dowel, which is replaced with a hollow one.
Drilled the case & didn't break thru the casting! Lining up the drilling:
And tapping for a 1/8bsp pipe plug:
Next, you have to re-establish connection to the pressure relief valve by milling a groove inside the bearing bore.
Theres the crank in the cases - in dummy bearings. Not ready to press the real ones in yet:
In other news, we sorted out some wheels. Want tubeless tyres, but still want spokes, to keep with the 'vintage' feel. Solution; a couple BMW wheels with crossover spokes which go into the rim edges rather than the centre well. Cut off the disc mountings on the front one. No front brake needed. Will get these chrome-powder-coated at Aerocoat.
