# Piston Rings



## chiliviking (Apr 13, 2008)

The plans for the Walking beam engine I am building does not call for any rings or other sealing device on the piston. This seems to go against my nature and I plan to put a single 3/32 ring on my piston. Anyone have any experience with engines without rings? The cylinder is cast iron and the piston will be 6061 Alum.


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## chuck foster (Apr 13, 2008)

i have built several gas engine models that use a cast iron cylinder and aluminum pistons with no rings and they work great.
now after allot of running they do ware and i have had to put a ring on the piston. when i say allot of running i mean about 600 or 700 hours of running.
 i would think that a steam engine would last longer because it would be running slower........just my uneducated guess.

chuck


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## raym 11 (Apr 13, 2008)

An lubricator in the steam supply will surely help, especially if you have oil grooves on the piston.
I seem to remember my Stuart engine drawings suggested this as an option. In any event I made the piston without seals other than the oil grooves and it works fine whether I am using the lubricator or not .
 I hope this is of some help. I used a similar design on my 'Little Angel' I.C. engine (cast iron piston and cyl sleeve). 

Ray


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## chiliviking (Apr 14, 2008)

What sort of clearance are you guys running in these no-rings engines?


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## raym 11 (Apr 14, 2008)

'slip fit' The reason for lubrication/seal rings grooves in the piston. In the case of the Shores hit and miss with a .500 bore, quality cast iron cylinder sleeve and piston works well for me.
 The Stuart steam engine was a brass piston & cast iron cyl I probably allowed  some clearance since it was my first attempt at machining a model (or anything else, for that matter ;D). 

Ray


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## Bogstandard (Apr 14, 2008)

Chilli,
If you are just running on air, a nice slide (0.001") fit with just oil grooves will be fine. Then just lap piston and cylinder together.

If you are going to be using steam, then a little more piston to cylinder clearance will be required, say 0.002". This is to allow for more expansion on the piston rather than the cylinder. In that case I would use a viton or silicon o-ring to maintain seal. They do require running in to get the correct D profile worn on, a couple of hours on air will do it. Once worn in they will last a fair while.

Hope this helps.

John


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## Mcgyver (Apr 14, 2008)

> I would use a viton



make sure you're careful and doesnt exceed the the safe temp for viton o rings....should be fine for a steam engine but they should never be admitted into the shop with the knowledge that they produce hydrofluoric acid at higher temps, very nasty stuff by all accounts. A steam engine shouldn't get that hot, but i can just image someone not aware inadvertently subjecting them to a torch or something and its goodbye hand or finger


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## Bogstandard (Apr 14, 2008)

Thanks for that Mcgyver, I do usually mention it.

What a lot of people don't realise, under the hoods of their cars lurks DuPonts' Viton. Anywhere there are high temperature joints that require an o-ring seal, it will usually be made of Viton. So if your engine ever catches fire, give it a good wash down before sticking grubby digits in there. Your fingers will not appreciate coming into contact with the acid produced, they are usually amputated with no questions asked, to stop it doing any more damage to your body.

John


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## chiliviking (Apr 15, 2008)

Could we now get some input from the other side of the fence, those in favor of a ring to seal the cylinder.( Maybe I'm the only one on this side of the fence)


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## raym 11 (Apr 15, 2008)

In my other life I was involved in the start up of a pilot chem plant that used hydrofluoric acid as a carrier in a polymer process. 
It was full suit and scuba breathing . Any contact with hydrous HF on the skin needed to be treated with injections of calcium between the affected area and the bone in order to neutralize the acid before it could neutralize itself by consuming the bone. There were some nasty outcomes.
 Vi ton as well as other polymers such as Teflon can be lethal especially when heated to the point of vaporization and inhaled. 

Ray


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## Bogstandard (Apr 16, 2008)

Chilli,

It has got side tracked slightly, mainly due to my post, sorry about that.

What sort of ring, 0-ring or metal ring?

Will you be using steam on it?

What I ask is important.

Yes, I do advocate the use of piston rings, in the right situation, and I use them in all my production engines.
They take a bit of bedding in, but afterwards you will find you will have a more efficient running engine.

If you can supply the info above, it is a fairly easy, but needs accuracy to do well.

John


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## compound driver 2 (Apr 16, 2008)

Hi
Even at 150 PSI of steam you would be very hard pushed to reach the decomposition point of Viton.
The only way your likely to have a problem is if you burn a viton ring in a fire box or with a torch. 
The place I wouldnt use Viton would be in flame engines and the like. Temperatures could in principle hit decomposition temperatures for not only Viton but PTFE another one you want to avoid over heating.

Cheers Kevin


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## chiliviking (Apr 16, 2008)

Yeah things kind of got sidetracked as what I am considering is a metal ring not viton.  The last engine I built used a ring that I recognized from my transmission rebuilding days during drag racing as a sealing ring. I'm not sure of the composition (cast iron etc.) but the way they have a locking tab at the gap makes them very efficient at sealing. I plan to run the engine on compressed air but don't want to build it in a manner that steam would be precluded later.


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## compound driver 2 (Apr 16, 2008)

Hi
cast iron rings are easy to make. takes about 15 minutes including normalising them. 

Machine them to the piston size split with a chisel file the ends of the split shim the ring open a few thou clamp between soft iron washers and hold the lot at red hot for ten minutes then let the lot cool slowly. Polish the ring and there you have it.

Cheers Kevin


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## Bogstandard (Apr 16, 2008)

Kevin has answered it spot on.

I think he has a lot more experience than myself at metal ring making.

John


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## Mcgyver (Apr 16, 2008)

Kevin, are you not turning after splitting and filing? how do you get the outward pressure on the cylinder wall and at the same time proper fit, ie the correct radius on the ring? One way is to turn the ring over-sized, split, file out a small section, then compress and clamp in fixture and turn to cylinder ID.


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## zeusrekning (Apr 16, 2008)

The way I have read to do this in the past is a combination of Compounds and Mcgyvers method. Turn the ring a couple thou over the cylinder dia, split, file then place the ring into a dummy bore (A piece of scrap steel with the same bore as your cylinder) using the piston , push the ring into the bore. You use the piston so the ring is square with the bore. Then heat the ring to a slight red glow and alow to cool. 
Tim


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## compound driver 2 (Apr 16, 2008)

Hi
THe act of shimming the ring open gives you the fit to the bore. As a rule shimming by 2 or 3 thou is more than enough. Compressing into a bore after machining over size could lead to an out of round ring. Not saying it wouldnt work but I wouldnt use the method.

All thats required after heating is a lite clean up with some scotch brite to remove the scale. I have run rings with out cleaning the only result is mucky oil in the bore during run in. One of my first traction engines is still on its same set of iron rings that were made almost 20 years ago. From time to time i think about replacing them but never do and the seal is still pretty good.

Just before Christmas I had an order for 120 piston rings from 5/8th inch to 2 inches and used the method I listed for all of them. In total only three broke during making and four or five had to be rejected due to warping.


Cheers kevin


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## zeusrekning (Apr 16, 2008)

Kevin what do you mean by shimming the ring? On one of my two strokes there is a pin pressed in where the ring gaps are. Is this similar to what you are describing?


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## rake60 (Apr 16, 2008)

There are many well written articles on the subject.
Try this one. Piston Rings

Rick


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## Bogstandard (Apr 16, 2008)

If you are a member of F.A.M.E., Bob Shores wrote a very good article on making piston rings. It is in the tips section under Bob Shores.

http://www.floridaame.org/

Basically it is the same as Kevin has done, but you only heat up the area directly opposite the cut.

It all depends on how technical you really want to get. I have seen articles where you make up a compound ring of three parts, two scrapers and a flexi ring in between, to me way over the top. Just keep it simple. Also make a few extras, the smaller the diameter, the more you will break trying to get them on, unless of course you cheat, and make a two part piston.

Tim, I think you will find, the little pins are usually used on multi ringed pistons, just to stop the rings rotating in their slots and so stopping the gaps lining up and causing loss of compression.

John


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## compound driver 2 (Apr 17, 2008)

HI
Just before the rings are clamped between the soft iron washers a shim of steel is pushed into the ring gap. this opens the ring up a little to over piston size, once the ring has been soaked for 10 minutes it takes on the shimmed size so when fitted on the piston its a little over pston size and a good fit in the bore.

I have had a go at partial heating on rings, most crack when being fitted. The soaking at red transforms the iron giving it some degree of spring making it alot less prone to cracking. One other problem with just heating part of teh ring is they end up a long way out of round. More egg shaped and I have doubts as to how well these will work in the bore.

Cheers kevin


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## compound driver 2 (Apr 17, 2008)

Hi
Couple of cast Iron rings in a cast iron piston. The bore is 1 and 5/8th inch.


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## Alphawolf45 (Apr 17, 2008)

I'd like to see picture of ends of the ring that been made and then split with a chisel..If I were doing it I'd anticipate that the broke ends might be ragged looking like any other busted iron casting...Have a picture of a ring being split?


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## compound driver 2 (Apr 17, 2008)

Hi
You ever heard of a file? its the way the rings are cleaned up. Of course they look ragged when split.
Using a chisel is the recognised way of doing it.


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## Alphawolf45 (Apr 17, 2008)

Have I ever heard of a file? ...Okay I guess lurking is better than asking questions.




			
				compound driver 2  said:
			
		

> Hi
> You ever heard of a file? its the way the rings are cleaned up. Of course they look ragged when split.
> Using a chisel is the recognised way of doing it.


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## doubleboost (Apr 17, 2008)

The pegs on pistons are only fitted to 2 strokes they stop the rings turning so a ring end wont get stuck in the exhaust port with nasty results
I made some rings for my marine engine from mailable iron pipe fittings they work great (on compressed air ) ,i have yet to feed it on steam 
John


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## zeusrekning (Apr 17, 2008)

Alphawolf45  said:
			
		

> Have I ever heard of a file? ...Okay I guess lurking is better than asking questions.


I too thought the comment was unnecessary. Maybe someone is having a bad day? I am also but I'll see if I can clarify the chisel method is a less abrasive way. If you were to cut the ring, the ring gap would be way excessive. Even with the smallest cutoff wheel in a dremel. By breaking the ring with a chisel you wind up with almost no gap and can file the gap you want in while cleaning up the edges with a hardened flat bar that has teeth cut into it. :
A good sharp chisel should crack the iron easily. 

Don't let one rude comment deter you from the wealth of knowledge found here. Most of us less knowledable folk here are learning well together.
Tim


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## Cedge (Apr 17, 2008)

Compound... 
Totally uncalled for abrasiveness. We can't all be perfect. Is it really all that difficult being social or is grouchy just your normal default mode?

Steve


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## Alphawolf45 (Apr 17, 2008)

I have bought rings for the steam engines I am building, an iron ring breaks nice and straight?...As I stated I would thought itd be too rough edge.....
.
 I figure he was having a bad day, .fortunately I am doing better,.I am having a real good day,not to change the subject but this morning I cast a brass adaptor to install new torch on my Tig welder..The casting come out mighty nice.....I thinking I will try making a Pemberthy injector, hence a renewed interest in casting brass.Takes lot more heat than the aluminum castings I make all the time..
.
.
.
.





			
				zeusrekning  said:
			
		

> IA good sharp chisel should crack the iron easily.
> 
> Don't let one rude comment deter you from the wealth of knowledge found here. Most of us less knowledable folk here are learning well together.
> Tim


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## raym 11 (Apr 17, 2008)

I "break" my rings by placing in a good machine vise, scribing a line on one or two sides close to the vise then lightly clamping with an old micrometer adjacent to the scribe lines. I then 'wiggle' the mike until a fracture occurs at the scribe line. I then carefully clean up the endswith emery board or small file which in turn creates the gap. (001-003). I haven't tried the hammer and chisel method but it probably works as well. The largest rings I've made are 1.250, most are .750.

Ray


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## Lew Hartswick (Apr 17, 2008)

ElGringo  said:
			
		

> lightly clamping with an old micrometer adjacent to the scribe lines. I then 'wiggle' the mike until a fracture occurs at the scribe line.
> Ray



 Do you also use that as a C clamp? 
  ...lew...


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## raym 11 (Apr 17, 2008)

No Lew, but I often use it as a hammer when I do precision chisel work 
Starret just dosen't make 'em like they used too. :'(

Ray

You might check out&#160; http://www.modelenginenews.org/feeney/pg8.html 

Following is excerpt from Feeney's log using the infamous George Trimble Method

The next step is to snap the rings. I've made the George Trimble ring cleaver, seen in use here. The two blades were stacked in the Quorn for grinding and marked so that when dropped into the channel, the blades meet precisely at the points. The slit that positions the ring is precisely at 90 degrees to the blade channel in both axis, hence theory says that a ring cleaved using this tool will have a perfectly radial break. I've heard more than one experienced model engineer say that they still prefer to snap rings between their thumb nails, even though they've built the Trimble cleaver! All I can say is it worked fine for me. The two rings at the left rear in this photo have been cleaved, but I'm damned if I can spot where...


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