http://vwdiesel.net/phpBB/viewtopic.php?t=6948&highlight=bore"i measured 2 1.6na blocks and got pretty much the same results. The top of the bore is quite thick over .300 all around and between cylinders is about .440 But where the BIG problem is further down between the cylinders. There the most i saw was .160 Every where else is down the bore is a little over .200 on all sides. Now to answer the question of this post can you fit the 1.7 pistons in this block? Personally i would not because stock bore is 76.5mm 1.7 is 79.5mm. That in terms of thousands is .120, or .060 each side that would need to be removed. It wouldn't leave enough meat between cylinders in my opinion. You could do it but your wall would be pretty damn thin. Now in my research i found that the 3/4 of and inch down and up is the thickest part. This is where i got readings of .300. The casting is slightly thinner futher down after the 1st 3/4 of an inch. After studying my readings i have come to the conclusion that the casting is slightly egg shapped so that coolant can pass/circulate between cylinders.
I would bore to fit 1.7 pistons at your own risk!"