Assuming the bore is 3.189 inches, set the gaps as follows:
Upper ring gap
006" x 3.189 = .019" (Turbo engines only)
Second ring gap
0065" x 3.189 = .021" (Turbo engines only)
Note: The above numbers
are for an 81mm engine (3.189"). You will need
to adjust your calculations based on the size engine
you are building.
Don't adjust the gap on the rails, just make sure it's
between .010" to .050". Just check one, not
all eight as this is not a critical measurement. If
one is within spec, they all will be in spec.
All measurements listed here are in inches, not millimeters.
If your rings already have a much bigger gap, they are
the wrong rings. If the rings overlap each other, they
are way too big and are the wrong rings. Contact the
company that supplied them to you. Do not try to fix
them by grinding that much off.
If one of your ring gaps winds up at .022", it's
not the end of world. Just remember, it's easier to
take it off than put it on.
The important thing when measuring the gap is to be
sure the ring is perfectly centered in the cylinder
and straight. Spray cylinders with WD40 before putting
ring to be gapped in the cylinder. Once in the cylinder,
use the top of a piston to push the ring down about
an inch, keeping the piston straight in the bore. Be
careful if you are using a piston with a dome so that
you are not hitting the dome when aligning. That could
make the ring sit off center in the bore.
Do the second ring gapping procedure first as they are
a much softer ring than the upper ring and take very
little filing to remove several thousandths.
Also remember to deburr the area you filed before doing
the final install of the ring onto the piston. If you
don't do this two things will happen. One, you will
scratch the cylinder wall and two, the ring will not
be able to spin freely when installed on the piston.
The best deburring tool is a cheap and small knife sharpening
stone. They are about $3 at most hardware stores.
If you do not have a ring gapping/grinding tool, here
is an easy way to file the rings. Take a smooth metal
file and lock it in a bench vise. Gently place the gap
around the file and pull the ring toward you. Important:
File only ONE side of the ring and not both sides at
the same time. You want to keep both sides of your gaps
as close to parallel as possible. If you only work with
one side, you will have the other side perfectly straight
to compare with. Re-measure the ring gap and proceed
accordingly. Be sure to deburr the ring with a smooth
stone when the gap is set.