17 lower, and 19 upper.
Measured in thousands of an inch. (.17 on the feeler gauge... and .19 on the feeler gauge...)
Last thing you want is the upper ring to seal more than the lower one.. this will cause the pressure trapped between them to flutter the rings, and could cause them to break/crack.
Also the gap is not that huge of a leak in the real world.
You have the gaps on different sides of the piston in the first place.
You also have quite a bit of blow by that escapes around the ring/piston and bore wall v/s the small gap area on the ring alone.
Bigger gaps, and why I set mine near the open end of the spec for the ROSS pistons was to ensure that they never, ever will expand and stick, and cause a flutter from trapped pressure.
I was talking to a race engine builder. He said he used to just coat the piston and rings with 30wt engine oil when he assembled his motors, and then one day noticed a guy using WD40.. So they got to talking, and the guy using the WD40 says his theory is that the light weight oil is only needed to lube the rings for installation, You don't really want the rings to NOT scrape the bore, you WANT them to scrape the bore.. (Think about that, it is the only way you can get your rings to seat, and seat quickly...)
Also the light weight oil does not build up as much carbon when it is burned off when you first start the motor... however, I think there is some oil that does get past the oil control rings, so I'm not sold on the idea that starting with WD40 keeps your rings cleaner forever, but why not start cleaner if you can?
Just my.02, I built my current engine lubed up with engine oil... LOL (But I would have used WD40 had I known this tidbit before then...)
BTW, ONLY on the piston rings. Lube the skirts and oil control ring with engine oil... and make sure you use a good assembly lube on your bearings and other friction surfaces to keep bearing wear/dmg to a minimum when you do that first start up of the engine. (It helps to crank over the engine with the CPS unplugged, or if you have an accusump, you can pre-lube the engine too.)
Good luck on fitting your stock rings. I don't see any reason you can't file them to fit if they are too tight. Just be very careful, take lots of readings, and use an old piston to set the rings down about 1" from the block deck for an accurate reading. I fit mine to each bore, and kept them seperate with each piston for each bore. (Sharpie pens rule to mark stuff up. Use dots for your rings... IE: 1 dot is Cyc. #1... Or just put the rings onto the pistons when you gap them, and mark each piston for each bore.. (Less dots to worry about..) Make sure you don't scratch your pistons with the sharp edges of the rings. Also do not twist your rings, it could break them, or stress them more than you'd like, causing a place when they can break later.
