Haha, hello Crojack, I am betting you are on the west coast and that bike was one of maybe two that fella had for sale, I liked it a lot and hoped someone with the right state of mind would buy it!
I posted about it on Brit bike for sale forum and started an argument about the style of the CL ad...and it had a rod sticking out of the case. It looks pretty good if that is the one. The cases are hard to find of course, the recent San Jose show had basically none for sale except for a couple of rusty boxes of transmissions and maybe some well encrusted cases...so buy whatever you can wherever you find it, and explore repairing those cases. I hope someone will leap to correct me but I think the A7 and A10 semiunit were only made for 2, maybe 3 seasons....no books handy.
That engine was pretty strong and fast and was a winner on flat tracks in the us for a few early years in the 50s, the A7 version was partially successful and well represented in AM racing. Gene Theissen did I think 123mph on El Mirage was it?..
As I recall there was a spare motor and crank and he was hinting he would sell another one...if this was the Oregon craigs list ad I was on about.
Of course it could be a coincidence....
whichever, congratulations, that is an interesting motor and pretty special in it's way.
The history is that it is I think the first BSA 650 and at that point was still, to my mind, the best design in that the engine and transmission were bolted together, saving about 3" in overall length from the later preunit design.
The transmission and engine share a lot of parts with the later pre-unit design, I have read this was called the semi-unit design. I think the clutch and transmission main shaft are different, some of the later parts can work, and I think that clutch was well regarded....may be wrong..again, heh.
I have the A7 version of it. I think it is a very nice looking design, perhaps the best of the 50s'and 60s for BSA and triumph...well, except for the Gold Star single.
But think what a tidy bike it would have been, a 650 twin as big/small as a B50...in 1954...but instead they made it all bigger.
Anyway...you came to the right place, well done. You will learn much, grasshopper.
The essential engine internals and transmission stayed mostly the same when they seperated the engine and transmission for the swing arm design thru about 1962/63.
I am maybe going to put my engine and trans into a B44/B50 frame..it will almost fit, I have hammers AND tongs.
But you, you have many of the bits for a good useful plunger framed 650, even enough for maybe a full restoration.
Good luck!
