Having got started on stripping the engine, I was intrigued by the markings on the piston.
It appears to have had some enthusiastic decoking during its life - the cylinder head is pristine.
Does anyone decode the stamped markings. It seems to be:
40/633 BSA
m/m OS
8/6/72
I'm intrigued that it appears to have an oversized piston measured in mm, but preceded by a fraction?
40 633 is the part number for the bare piston (40 632 in parts book is piston with rings)
It is 8:1 compression.
8/6/72 is the date of manufacture.
See below for the part number. You can see the compression ratio in the parts book.
Thanks Julian.
And I see that '+1/2mm' is effectively '+20' thou, which is the units I would have expected.