A65's are unit construction, A10's are pre-unit. The A65 is a sweet bike, there's no doubt about that. I wouldn't mind buying another one, one day. Maybe when all the billy lids are left home and my money's my own again
But then again, if I had the money I'd buy another B34 Gold Star - they're like the BSA equivalent to a Cooper s.
If you do get hold of an A65 kazjim, there's a couple of mods that are worthwhile considering (unless you want to keep it original of course). One is to bore and stroke it using the A10 crank. The pre-unit crank is a longer stroke and you can stretch the A65 to almost 750cc. (Not quite, I can't remeber off hand exactly what - about 730 or something like that). The other is a needle roller bearing conversion on the timing side main bearing. Both A10 & A65 used a plain bronze bush. The main problem with doing the conversion is that the bush supplies the oil feed to the crank. This is overcome with an external oil line into the timing cover with an oil quill into the end of the crank. I have never done this, but have seen it on a couple of bikes. It's an excellent mod for bottom end longevity.
M20's & M21's can be bored to somewhere near 700cc (again can't remember the actual capacity off hand) using a Subaru piston and the M21 flywheels. If I ever get around to putting my M20 together, I'm going to look into this a bit more. I've got a set of M21 flywheels to do it.
