slade69

Expander ring gap, is there such a thing needed or not? When I install oil rings to my cp bullet pistons, the expander almost seems to be too long. It's difficult to compress with ring compressor hard enough to get the oil ring OD to the same level with ring land OD.
Also, when I put the expander ring to my bore, it will overlap a bit. Should there be gap as in first and second rings? Or will the expander compress and "shrink" in diameter?

joe_padavano

The "corrugated" design of the expander allows it to expand and contract radially. Just butt the ends. There is no set gap. Do NOT overlap the ends. It's supposed to be tight. Note the small tabs that fit behind the upper and lower oil rings - be sure they are behind (inboard of) the oil rings.

slade69

Yes I understand the end has to butt, not overlap when installed on the piston. Also I noticed the small tabs you mentioned, but only after I tried to assemble the support rails first, wondering why the expander does not fit. The expander needs to go in first, just because of those small tabs.


The corrugated expander makes the oil ring assembly really tight. I'll try to assemble piston in the bore today. Let's see what happens.