How I made my piston rings. No heat

[paulc]

G'day guys, I thought I would share my method of making piston rings, I have not heard this technique discussed in any the forums, but then again I don't get out much, so it very well may have been.

In 97' I designed and built my own 7 cylinder radial, the heads were inspired by the Hodgson engine, but the rest was all mine.
The engine runs really well, still even today.
The piston rings were made from a good grade of close grain cast iron using a method a local Aussie model builder showed me in person, this before the internet! No heat was used. So no distortion and perfectly round rings using this method.
The method starts by parting your rings off to near width with good meat on the OD and ID. Then in the mill, the ring gap is machined to the desired size. Over to the lathe you make a simple turning fixture with a face clamp that holds the newly milled ring gap closed. I made a tapered sleeve to gently tap over the ring to close the gap, clamp the face then tap the sleeve off, then simply turn the OD of the ring to your desired bore size.
The ID is turned to final size in the same way only with an OD clamping fixture holding the gap closed. I'm sure you get the idea.
I used some fine sand paper on a flat plate with some WD-40 using a figure 8 pattern to give the rings a nice smooth surface on the faces.
These rings worked great.
Each to their own but after using this method I would never consider using any heat to make piston rings.

I've included some of the parts here, folks may find these of some interest.
Cheers Paul

 

[GreenTwin]

Very nice parts there !!!

.

 

[srobovak]

Hi Paul,

An interesting method of producing the piston rings. Do you have any pictures of those lathe jigs you're talking about?
Do the rings spring back to opened gap when you release them from the clamping jig?

Thanks and cheers,
Branislav

 

[paulc]

Hi Paul,

An interesting method of producing the piston rings. Do you have any pictures of those lathe jigs you're talking about?
Do the rings spring back to opened gap when you release them from the clamping jig?

Thanks and cheers,
Branislav

Hi Branislav, yes of course the ring will spring back to the normal wide open gap state. Because the gap was physically machined in when the ring was complete and relaxed so to close the machined gap requires force. In the rings relaxed state the gap is wide open.
Where as IMO the less desirable heat treatment method sees a ring first split, then the split stretched open to make the gap, the ring is then heat treated to so as the gap remains open when cooled. The issue with this method is the ring can suffer from distortion from all the heat. Plus uniformity from the heat treatment process is questionable.

FIXTURES?
I have no pics, but my fixtures were basic. To turn the ring's OD a simple mandrel with a shallow spigot to locate the ring blank on with with a face clamping washer to hold it the ring and gap shut. A simple hollow tapered sleeve was used to close the rings gap, while the face washer was tightened. Remove the sleeve, gap remains clamped closed and simply turn the OD to your desired bore size. When you let go of the face clamp the ring will spring back open.

The same process for the ID. Only this time ring gap is held closed via the OD so as you can turn the ID. Again when the ring is removed the gap springs back open. The OD and ID are perfectly round.

 

[paulc]

TIP: With the gap held completely shut you turn the rings to bore size. This will see the ring have zero gap when the ring is installed into the cylinder. That's fine leave it at zero! Because a small clearance gap will soon open up with just the slightest of wear on the first run.
This is perfect for small model engines.

 

[Jojo]

Paulc,
Mr. Paul Breisch included a drawing with his casting kits of exactly the method you are describing.
I haven’t tried it as of yet but I plan to on my next project.
by the way, your work on the radial is truly beautiful

 

[bluejets]

No thanks...I'll stick to the heat treated ring with adaptor for final turning to size/round later.

 

[Steamchick]

Paulc,
Mr. Paul Breisch included a drawing with his casting kits of exactly the method you are describing.
I haven’t tried it as of yet but I plan to on my next project.
by the way, your work on the radial is truly beautiful

I was taught (1960s in an engine refurbishment workshop) that ring gaps should be 0.001" per inch of bore diameter, when gap is closed in the bore. For cast iron rings in cast iron blocks/bores. It is hard to measure sub-0.001" gaps, as the feelers are so fragile! Remember, the gap is circumferential, so 0.003" at the GAP, relates to about 0.001" bore DIAMETER. (Pi x Dia.). Ergo, for a model engine with sub-1" bore you want sub-0.001" gap, which means sub-0.00031" of lapping(running-in) from the closed-gap bore.
The tangential load of the installed ring is developed from the compression of the ring from the free state to bore size. But this should be kept low, to prevent excessive wear, as the real load when running comes from the addition of the gas pressure from combustion to the pre-load from assembly.
K2

 

[Shopgeezer]

I like this method. No messing with heating, breaking the rings etc. Haven’t done a ringed engine yet but when I do I will definitely use this method.

 

[bluejets]

2 thou per inch on air cooled engines.

 

[L98fiero]

Then in the mill, the ring gap is machined to the desired size.

In my visualization of the way this works it sounds good but is there a rule for the 'desired size'? Obviously a larger starting gap means more spring pressure and you can't start with the final gap distance or you'll have no spring pressure, is the gap you mill comparable to the pin size used in the Trimble method or it's variations?

 

[L98fiero]

This is a bit off track to the original post but ring making related.

Has anyone ever done an FEA analysis of the stresses from making a ring with the Trimble method? Maybe I'm out to lunch on this but it seems to me that there would be a high stress area opposite the gap when it's in the fixture which would result in distortion when it's heated, and heating them with a torch while they are hanging from a pin would be asking for trouble as the heat could be concentrated in one area if you're not careful or the flame isn't diffuse enough. Paulc's method seems better because it avoids that high stress concentration.

 

[petertha]

Trimble's method doesn't suggest hanging the rings from a pin/bar or flame heating. The Trimble SIC article prescribes the exact sizing, and matching fixture that constrains the opened rings in a very specific way. The heat process is fully described & much more controlled vs flame. There is a loooong thread on the forum that went into a lot of detail on this subject. Maybe that's where the confusion originated - someone called it the Trimble method, but it had little in common , at least where it counted.

 

[L98fiero]

Trimble's method doesn't suggest hanging the rings from a pin/bar or flame heating. The Trimble SIC article prescribes the exact sizing, and matching fixture that constrains the opened rings in a very specific way. The heat process is fully described & much more controlled vs flame. There is a loooong thread on the forum that went into a lot of detail on this subject. Maybe that's where the confusion originated - someone called it the Trimble method, but it had little in common , at least where it counted.

I realize the Trimble method doesn't suggest that, and neither did I though I've read on this forum, people doing it, so obviously it happens, and that wasn't the question. There is no confusion on my part in that regard.
I'm not an engineer but it seems to me that because of the pin that is used to spread the ring in the Trimble method, that there would be a stress concentration opposite the pin and I asked if anyone had done an FEA analysis on a ring stretched open in that way, not whether heating with a torch was an acceptable way of heating the ring/fixture.

 

[petertha]

My understanding is the heat set is to normalize the ring on the prescribed dowel spreader pin. Once cooled, the ring should have little to no residual stress. The shape will be different than circular but open gap should still essentially match the dowel diameter. So not quite sure what FEA would tell you at that juncture. Once compressed into a circular bore, the ring exerts (ideally very uniform) radial force around its perimeter which is the goal. So the interesting FEA exercise (IMHO) would be to take that un-sprung, post-heat set shape, then constrain it to it's appropriate circular bore & then see how the FEA stress colors up. If its an even band around the perimeter I guess you could say it proves what we already know - the method works. But accurately defining the un-sprung heat set ring shape geometry I imagine would require some accurate magnification / digitization to first build the CAD model. Would make a great project if someone had the equipment or maybe university study project. It's been a while since I read the SIC article, but I think that's essentially how Trimble developed the sizing equations from base principles. I believe he noted the resultant shape correlated quite closely to un-sprung FS rings. Anyway, as mentioned there is another long post on all the Trimble stuff. I won't further derail this post which about a no-heat method.

 

[paulc]

In my visualization of the way this works it sounds good but is there a rule for the 'desired size'? Obviously a larger starting gap means more spring pressure and you can't start with the final gap distance or you'll have no spring pressure, is the gap you mill comparable to the pin size used in the Trimble method or it's variations?

The Trimble heat treat (hot) method uses a spreader of a certain size to form the desired gap, If using my adopted (cold) method you would still use the same gap only you would machine the gap, this is done BEFORE the rings are finished. The end result will be the same, well not really as using my method the rings are guaranteed to be perfectly round where as using the hot method what you get after heat treatment you are stuck with.

Again, with the method I described here is no heat treatment required and the rings final ID and OD are turned round after physically physically holding shut the pre machined and sized ring gap. To me this was a no brainer. As I'd read several stories of distortion and the resultant unsatisfactory ring production using methods involving heat treatment, splitting and spreading. Keep in mind these small engines cant really afford to leak much gas as they are already very small and don't have to lose much seal to not run at all. The rings really need to be near perfect. The smaller the engine the nearer to perfect they must be.

For those interested here is a scratchy old VHS tape video of when I first ran the engine for a group of close friends. It was 1997 I was about 29 years old.

 

[paulc]

There is no doubt the Trimble method has made good working rings in the past and yes I recall there was a special tool used to hold all the rings accurately while being heat treated. And it would want to as those tiny parts would go bananas with distortion otherwise.
The splitting process used to cut the ring to my mind introduces another potential problem area.

Anyway each to their own. All I can say is the method I describe in this thread gave me excellent results and was a relatively easy process.
And I heard not heard it mentioned before.

 

[paulc]

No thanks...I'll stick to the heat treated ring with adaptor for final turning to size/round later.

My fellow Aussie, bluejets, You have stumbled into my thread, where I discuss making rings cold, using no heat treatment.
It's not a poll!

Seeing as you mentioned it, I wonder how much more beer I can buy from what I saved not having to purchase an oven?
But at least I fixed your ignition design, she sparks now right? ...hehe

 

[minh-thanh]

paulc !
Thanks for sharing another way to make rings !
I have a question :
If use this method, when I perfect the ID and OD of ring , I can just do it one by one, right ?

 

[Rocket Man]

I buy rings from Hastings Piston Ring company $1 per set. They have all bore diameters, all thicknesses & all designs. I can't make a set of rings for $1. Rings are sold by, bore diameter, thickness, design, not by engine model number or engine serial number. I bought 8 sets of rings to rebuild an engine for $9 plus $6 postage. At age 72 I don't have time to make my own rings I might be dead tomorrow.