I've got some new b18 rings will they work on b16 pistons? does anyone know?

 

If I remember right, the B18's bore is several millimeters larger than the B16's bore. So, in a word....No.

 

i thoiught they both have an 81mm bore

 

Hmm, so they do... on me for not looking harder at first. Try putting 'em on the piston and measuring the end gap...if it's within spec you should be good (assuming the B18 rings fit into the B16 piston's ring lands).