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Ring Gap for 81mm bore for TURBO engines only
#1
Handy little guide for the DIY'ers

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.

Oil rails....
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.
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