Hi all!
I start talking about the bike of my avatar, a BSA A7 1949 I started to restore.
I don't know if it's all same around the world, but here in Argentina, ALL the BSA cylinders are cracked and patched up. My bike was not the exception (of course!).
After verifying it, the mechanic adviced me to get another cylinder...(you know it's not just going to the supermarket)...anyway, after a hard research I found a guy who was selling a god blessed BSA cylinder. It was cracked and fixed, but usable.
This guy was an old school mechanic, who once upon a time talked with an engineer that used to be the BSA Technical Country Manager about this issue.
The engineer told this guy that the problem (in Argentina) with the cylinders was that everybody used to rebore them at 90°, ignoring that the angle of turn of the cylinders was not 90°!!! This error generated an extremely thin cylinder wall, which eventually would break.
However, if it's not 90° the question is: which is the right degree of the cylinders?? Anybody has this information? If not, it's still a nice data to bear in mind!!
regards