Hi just cleaned some sti pistons up that came out of a 98 block.
all pistons look the same all numbered under neith the same,
but on top ones stamped with a B other three a A
any ideas any one

 

The A & B on the pistons are size gradings.
On 92mm engines its A= 91.985-91.995mm B= 91.975-91.985mm
The block should be marked up also for bore size
A= 92.005-92.015 mm B= 91.995-92.005mm

Hope this helps.

 

just measure the bores m8 and as above A and B stand for different sizes