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The decision by Niagara Piston Ring to no longer make piston rings under 8" diameter really threw the old gas engine in a mess. This forces one to the shed to try a hand a making a few. Rings were needed for 2 engines, one a 5" bore and the other 4 3/4" bore. The rings grooves in these piston had gotten very sloppy and they were each chucked in the lathe and cleaned up nice and square. Now new rings were certainly needed to fill the wider ring grooves. Making rings is probably old hat to the model engine guys but for us big engine guys it's always been far simpler to just order what we needed. So here is the tale of making them.
A suitable piece hollow round grey cast iron was ordered from list member Tony Leonard of DuraBar that both sizes of rings could be made from. This was chucked in the lathe and the ID was bored to the same ID as the expanded rings being copied. The OD was turned about .100 larger than the OD of the rings being copied. Once turned back far enough, the rings were parted off about .020 wider than needed.
The rings have been parted off and a .625 wide space removed. The .625 wide space was derived by simply copying the space on the old rings being duplicated.
One of the new rings was squeezed shut and wired to stay closed. Using thin wire assures uniform squeeze all the way around. The ring is now oval shaped about 0.100 and would be worthless in an engine. The ID is carefully measured at the smallest dimension of the oval.
Once all the rings were made for the 2 pistons, the left over material (about 2" long) was rechucked in a smaller lathe from the inside and pushed fast against the steps on the jaws. Then a step was turned true and square, slightly shorter than the narrowest ring. The step diameter is the same as the smallest ID on the new rings when closed.
A clamp plate was burned out of 1/2" plate and cleaned up on the OD to 5" and a 3/4" hole drilled in the middle.
Next the clamp plate was mounted on the fixture using a 3/4-16 draw bolt (all thread) going all the way thru the quill with a washer and nut on the other end. Then the end was faced to assure good and straight. This true side will be turned against the ring firmly holding it in place.
With the clamp plate removed the squeezed rings is placed on the turning fixture. You can really see the ovality !
Now the clamp plate is placed (turned face toward the ring) and the draw bolt installed and pulled tight. The fine threads really aide getting it clamped tight.
The the ring is turned carefully to the exact diameter of the cylinder bore. In this case 5.003.
Repeat and in short time you have turned to fit rings.
And a close up.
The only part remaining is to surface grind the rings to the correct width and to set the gaps.
It would still be easier to just call in an order, but at least now I'm satisfied a hobbyist can make them if he really has to.