I went to the engine place today and made a load of measurements:
centre of crank to top of block: 216mm
con rod centres: 145/144mm
con rod hole to top of piston: 30.35mm
half stroke is 86/2=43mm.
Now if I do 216-43-144-30.35 I get -1.35mm.
This means that the top of the piston sticks out the block by 1.35mm when the piston is at TDC. Is this right? I didn't expect this answer. It doesn't mean that the piston rings are out of the block since they sit 5mm down from the top of the pistons.
Anyway, I also did a load of compression ratio calculations.
Std 2.0 8v engine is 10:1
B+ head reduces head vol from 47cc to 43cc
This raises CR to 10.5:1
Rebore alone would rise it to 10.6:1
8v head on 16v block would make 12.66:1
So I need to skim about 2.15mm off the pistons to give me 10.5:1.
I had to guess the 8v piston pockets etc. If anyone has an 8v Sri piston kicking around I'd appreciate the approx measurements of the pocket etc.