Mazda 1.6L Piston Ring Information and Sizing Differences

There is a tricky thing regarding the 1.6L piston rings regarding the size of the oil ring groove. We've had a number of customers report the oil rings do not fit correctly on their 1.6L pistons, and we've found that there are differences between some of the pistons with their oil rings. The Miata should have a 4mm oil ring groove and if you've found that your pistons have a 3mm groove, they are likely from a B6Y2 engine found in the Protege or MX-3. It's probably a really common oversight when an engine has been rebuilt that the wrong pistons were installed, as everything else is the same except the oil ring groove, so the lesson is to ALWAYS measure your pistons (and all engine parts) BEFORE ordering parts for them!