A new attempt at making piston rings

[brian Rupnow]

Let me start out by saying that I have made my own piston rings in the past---and failed dismally. I was so disheartened by my failed attempt that I went to Viton o-rings and never looked back. Now I have ten or twelve years engine building experience, and I am going to try again. I have a 1" bore side shaft engine which I built a few years ago with a Viton ring, and it runs very good, and has incredible compression. I have chosen this engine because I can undo the con-rod bolts and remove the piston without disturbing any of the other engine settings. This will require that I machine a new piston and two rings.

[brian Rupnow]

After considerable reading of books by Malcolm Stride, Philip Duclos, L.C. Mason and various posts by George Britnell, I have compiled this list of things related to ring making. This information is not "absolute", as some of the information given by one author tends to disagree with information given by a different author.

[brian Rupnow]

The drawings below show the piston "as built" for one 1/16" cross section Viton o-ring, and the same piston redrawn for a piston that accepts two cast iron o-rings to match the rings supplied by Debolt. (I will be making these rings to the same dimensions as two rings purchased from Debolt for my Vertical i.c. engine-2021). Note that nothing on the piston changes except the information relating to ring width, depth, and location.

[Sparky_NY]

Article I have in Strictly IC magazine used a different approach. The important factors were getting the ring to have tension against the cylinder walls and at the same time maintaining a perfectly round shape for good sealing. In that article, the made the blank rings in manners like you listed, made a fixture holding a HSS bit sharpened to split the ring. Another fixture was made to hold the rings open with tension, then heated in that fixture to "set" that expanded condition permanently. That fixture was the key to getting perfectly round rings that would seal well around the entire circumference and have the proper even outward tension.

Some of the other methods produce a ring that is not absolutely perfectly round and having even tension against the cylinder walls. That is the magic of making good rings. Turning blanks, parting off and hand finishing the thickness is the easy part.

A surface grinder is the best way to do the thickness, all the rings at once, they come out identical with a superb finish. Needless to say, you have to have a surface grinder available.

Many, if not most of the miniature engines I have seen only use one ring. (commercial and homemade)

Many have done it, you can too! Just don't give up !

Edit: The method from Strictly IC magazine is known as the George Trimble method. It is the method with the most reported success in the model engine community. There are descriptions of the method all over the net with a google search.

[brian Rupnow]

The first thing I wanted to check was---Does my .062 wide cutting tool cut an .062" groove in cast iron on a straight in plunge cut. Apparently not. The cutting tool does actually mike at .062 wide", but the slot it cuts in cast iron on a straight in plunge measures 0.057" wide. The top of my cutting tool has a strange shape to it (as bought) so next thing I'll try is grinding it flat and then do this test again.

[brian Rupnow]

Okay--After a regrind of the top surface of my parting off tool so that it is absolutely flat and a second groove cut in cast iron, the groove is still measuring .057" wide. That's okay. As long as I know, then I can live with that. I could regrind an hss toolbit to give me an exact .062" groove, but I don't really want to have to do that.

[eKretz]

I wouldn't do that anyway, regarding cutting the groove. You want to be able to finish with a nice light cut on both sides to get a very clean and true surface so that the ring has a good sealing surface. Plunging straight in at finished width would probably not give you that.

[brian Rupnow]

This is an "end" of cast iron that I have had for years. It has been turned down to 1.000" outside diameter and bored to 0.898" inside diameter. Now comes the parting off and deburring. I will get as many .063"-.064" wide rings out of this as I can.

[nickel-city-fab]

Brian -- does this help any? https://www.youtube.com/watch?v=7L4rNagoOzo
Seems like it worked pretty well for him, his rings are around 1mm sq section
I've used similar techniques in the past to make large (8") rings at work.

[brian Rupnow]

eKretz---I think that is taken care of by sliding the rings around in a figure 8 pattern on a sheet of fine emery cloth, or on a sheet of glass with lapping paste.

[brian Rupnow]

I was able to part off 6 rings with no problem. The math is a little weird, and I don't really know why. The ring closest to the right side of the page is 0.070" wide, but was supposed to be .062" wide. I set my parting tool against the end of the piece in the lathe, then using my DRO I moved it 0.125" towards the headstock. In theory that should have taken a cut .0625" wide and left a ring .0625" wide. After cutting and measuring the first ring, I moved the cutting tool 0.005" towards the headstock and took another cut to clean up the end of the stock. All subsequent moves were limited to 0.115" and that yielded rings approx. 0.065" wide. That should be about right because the rings still have to be cleaned up on both sides with some fine emery paper.

[brian Rupnow]

Here we have the six rings, polished on both sides with 150 grit, then 600 grit emery paper on a flat cast iron surface with some wd40. The thickness of each ring is printed inside the ring. I will lap that 0.064" ring a bit more and bring it down to 0.061" thickness.
I don't know if I can bring the 0.070" ring down in thickness by lapping, but I will find out. The recessed fixture that I held the rings with while lapping them is in the picture, with an 0.040" recess in the face, but it doesn't show up very well. One of the websites I looked at before undertaking the making of these rings suggested deburring the inside corners/edges with a circular porcelain stone. I don't have such a thing, but will call around to my tooling suppliers in Barrie and see if I can buy one.

[brian Rupnow]

The two rings that were "overthick" both came down to 0.061" with a bit more lapping. I've read so much about making rings in so many different places, I can't remember where I read about the porcelain sharpening stone that was used to deburr the inside edges of the rings. Maybe I had it wrong. Maybe it was "ceramic" sharpening stone. It looked to be about 3/8" diameter x 4" or 6" long, and would have to be a reasonably fine grit. If anybody knows where I can buy such a thing in Ontario, Canada, please let me know.---Brian

[Dan Dubeau]

Lee valley have a good assortment of stones for a Canadian supplier.

[brian Rupnow]

Thanks Dan--They have a store in Vaughn, not too far from Barrie.---Brian