Oil rings are smaller than compression rings

[acolella76]

I posted this on two other BMW forums that must not be mentioned and got jack shit for responses so now i am out to hit the trifecta!

I was fitting new piston rings last night after I got my block back from being honed and discovered something weird. In all 6 sets of rings the two compression rings are PERFECT; The end gap is around 0.012"-0.015" (Bentley suggests 0.012"-0.020"). The oil control rings however gap at something crazy like 0.027" which is weird... And this is before I even filed them down. They just came out of the package like this. All 6 of them.

Piston clearance is fine... so I don't think that too much material was honed off of the bores. Is the gap fine so long as I clock them correctly? Really need some advice before I can move forward with the engine.

[LJ851]

It's not an issue from my experience. Most piston manufacturers only list a minimum clearance for oil rings, usually .010 to .015 inches. They are designed to not need gapping. My experience is primary with 3 piece oil rings, BTW.

[jlevie]

On the assumption that these are the three part oil control rings, the scrapers can have larger gaps. The gaps in the three parts should be spaced 120 degrees apart and not lined up with either compression ring gap.

[frankenbeemer]

You came to us last? I don't know what to say other than: I wish I knew. Then I could tell you I refuse to answer.

[acolella76]

It's not an issue from my experience. Most piston manufacturers only list a minimum clearance for oil rings, usually .010 to .015 inches. They are designed to not need gapping. My experience is primary with 3 piece oil rings, BTW.

Great, thanks for the info. The only one that needed to be gapped was the middle one, is that right? The middle one was waay bigger than the bore and needed to be filed down.

You came to us last? I don't know what to say other than: I wish I knew. Then I could tell you I refuse to answer.

Sorry, I still love you guys. Is that your Sprite in your avatar?

[frankenbeemer]

Is that your Sprite in your avatar?

No, I saw it sitting by the road about a year ago, and stopped to talk to it. It was on Hwy 281 just above Lake Toxaway, I guess it's still there. I'd have one, but my dog said no.