The great O ring discussion

[el gringo]

Well said gbritnell. I have many similar thoughts regarding the 'real deal'. that is a very us-full and thoughtful posting.
I have averaged ~ one IC engine a year since 1991 and never tried o-rings for pistons, even when self learning to be a model machinist in 1991. [my first IC was Bob Shores 'little angel']. I did use viton on the Rudenow's Henry Ford engine and it ran as designed.

I posted some pics on another thread ( raym/rupinow vert hit & miss) related to my way of going about it, that method of the flame not touching the rings leaves very little oxidation to be removed with a swipe of 600 grit.
Tis a good thing to see the almost mirror finish on the rings and cylinder wall after a brief pre run

 

[stevehuckss396]

One thing to think about is the o-rings do wear faster than CI rings. One of my pals had a complete loss of compression and of course it happened at a show. Thank god it was a hit miss engine and that made it easy to pull the piston and replace the o-ring. Due to fuel and oil being in the cylinder, heat and friction also a factor, they do have to be replaced from time to time. My first IC engine ran for the first time in 2010 and has not needed that kind of maintenance. They are easier to make (just buy one) but in the long term are a little more work. Both work equally well if executed properly.

 

[Nerd1000]

I suspect that there is an element of 'horses for courses' here. O rings appear (to my total newbie eyes) to be a route to simple and reliable compression in a 'demonstration' engine, but given that much of the heat that goes into the piston of an ICE is conducted to the cylinder walls by the rings, I suspect that a polymer O-ring (with its intrinsically lower thermal conductivity and heat resistance) is unsuitable for engines that are expected to operate under significant load.

 

[Donleybill]

Gentlemen,
I have been following the O ring discussion in another thread and have read several others in the past. Most of the builders on this forum have been machining and making engines for quite some time. That being said I have trouble understanding why there is such an aversion to making actual piston rings. If one follows the discussions about O ring use there seems to be more negatives than positives in their use. It seems everyone has their own guidelines for using them, type, O ring, X ring, material, Viton, neoprene, piston fit, loose, tight, cylinder wall fit, tight versus loose. When using piston rings there are hard numbers and data for their use. I feel that using O rings is taking the easy way out. Granted for a novice builder who would just like to build his first engine and hear it run I understand their thoughts but for the rest of us that have two or more engines under our belt I don't understand the aversion to making and using piston rings. Having built many engines over the years and following other's builds the biggest challenge in getting an engine running, bar none, is getting the valves to seat and seal properly. Hours can be spent machining the valves, seat cutting, lapping and pressure testing but yet we all accomplish this task one way or another. In building an engine there's so many somewhat complicated parts that need to be made, gears, cams, valves and crankshafts to name but a few and yet here again we are all able to do this but mention the word piston ring and some people get cold chills. To me making rings is one of the easier machining exercises connected with building an engine. You turn a piece of iron (very easy to machine) to a given I.D. and O.D. You then part it off to a given thickness. You break the edges then split the ring. If using the Trimble method a fixture needs to be made for heat treating. This is just another simple machining project. Now the heat treating. I don't have a kiln or heat treating furnace, I just use a standard propane torch. When making my fixture I hollow out the bottom so when heating there's not a lot of mass to heat up. Long ago i purchased a jar of Boron powder from a gun supply shop and after multitudes of piston rings I still have enough to last my engine building career. The rings are mounted on the fixture. The fixture is heated up then coated with the powder. The powder turns to a somewhat liquid coating much like silver solder flux. I then place the flame of the torch into the pocket in the bottom of the fixture so that I'm not applying the heat directly on the rings. I then hold the torch until the whole fixture and rings are brought up to a dull red color and once obtained hold it there for 2-3 minutes. The fixture is then allowed to cool and then the Boron coating is washed of with tap water. The rings are then unmounted, cleaned. fitted to the bore and gapped. Trimbles method and several other can be found on the internet for free and give a more thorough explanation in the making of piston rings.
To sum up my dissertation, why not give piston rings a try. It's really not that hard of a job and then you don't have to worry about all the issues of fitting and using O rings.
gbritnell

I found a consistent simple way to break the piston ring. I held the piston ring in my mill vise. With a 1/2” dia pin or anything stiff in the collet I side load the piston ring until it snapped. Lots of control, easy to do, broke clean every time. I made extra rings thinking I was doing this with a bench vice and hammer. Didn’t need them using this approach.

 

[johwen]

Folks
Following the "Trimble Method" is the way to go. Just a few extra operations but is worth while. However I deviate slightly by halving the width of the ring and put two rings in each groove with the gaps set 180 degrees apart. Making sure you have the correct clearance around the ring in the groove. A couple of strokes in the bore and you should have full compression ready to run. Just make sure that the RING OD is the same as the Cylinder bore and push the ring over a tapered bore to split. Have patience and give it a go Cheers. John Auto Engineer.

 

[gbritnell]

Gentlemen,
I had been following the ongoing thread relative to the use of O rings for model engines. It is now 3 pages long and contains a multitude of thoughts and ideas about O ring application for model engines. The ideas range from fit, type, clearance, longevity etc. Some have stated that they have many hours of running time on their engines with absolutely no issues while others say they just couldn't get them to work. In my reading of that thread I came to the conclusion that there were so many variables at work that I would start a new thread relative to the use of metal piston rings.

If one reads my original post nowhere in there did I say that O rings wouldn't work nor did I say that anyone who uses them is trying to subvert the model engine hobby. If you're happy using O rings God bless you. In further reading of my text my suggestion was that as accomplished engine builders why not try metal piston rings.

I started in this hobby building model steam engines. Some of the Stuarts I built had metal piston rings and others only required a graphite string packing. If a steam engine loses a little piston seal it will still operate. If the valve, D or piston, is a little leaky it will still operate. If the valve is a little out of time it will still operate. They are very forgiving engines when it comes to operating. On the other hand when building an internal combustion engine so many elements need to be exact or the engine will not function properly. The bore needs to be straight and concentric with the proper surface finish. The valves need to seal both at the valve seat and the valve stem. The engine has to have compression which falls back to the bore and valve conditions. Now you advance to the ignition. An I.C. engine needs a spark plug, a triggering device, points or Hall sensor, and in the case of a multi-cylinder engine a distributor. An I.C. engine needs a carburetor that will supply the proper amount of fuel.
We who have built running I.C. engines have accomplished all of the aforementioned things but yet in some cases (IN SOME CASES) struggle with the use of O rings so why not try metal piston rings.

These forums are about learning and passing on learned information and that is what I have always tried to do.
gbritnell

 

[ajoeiam]

Hi Group,

So many issues!


There is a thing called “progress” - I didn’t vote for it myself, we are just stuck with it.

I have a day job (retirement is for wimps) teaching engineering apprentices and lecturing in engineering. My last job in industry was as Head of Electronics at the European R and D centre of a global corporation that nobody has ever heard of. I spent my time working on time plans, spreadsheets, budgets, while in the labs just down the corridor talented engineers were doing the job I originally signed up for in my youth - hands on engineering research

I left industry when I accepted that if the brilliant young engineers leaving university and college did NOT have better ideas, better imaginations and better visions of the future than I had, then there is something very, very wrong with our education system.

So I teach my students to embrace the opportunities provided by exciting new technological developments, use CAD/CAM, 3D printing, CNC (or at least DROs) while in my hobby I still machine press-fits, turn by hand, and (to my lasting shame) know that I can file a part flat and true to with in a few thou in less time that it would take me to wrestle with the set-up of the part on my mill and rummage through a jumbled box of cutters in my disorganised home workshop. It is a case of “Do as I say, not as I do”

Hmmmm - - - - I, for one, would love to know that CAD/CAM, or even just CAD programs you use, recommend or whatever combination of that you care to offer.
3D printing - - - I'll start simple - - - - I would like to get such a system but - - - -which one?
Purchasing in north america drives the costs too high (imo) but purchasing in the far east significantly ups the risk.
Ideas, suggestions etc please.

 

[Richard Hed]

Hi Group,

So many issues!

Personally, I machine cast iron piston rings (or use graphite yarn for steam) because it gives me pleasure - if others want to use o-rings, that is their choice, there is no right or wrong

Regarding Vederstein’s comments about discouraging people from engineering as a hobby: There are far greater issues than a comment about differing techniques at play....

Finally, sources of knowledge: O-ring manufactures publish extensive data on the use of their products and operate technical advice and support lines. Of course accessing these resources requires spending time reading texts and understanding the engineering principles - unfortunately we live in a world where many people are reluctant to make that investment and would prefer to re-invent the wheel through trial and error

I would suggest that most group members can stop reading this post at this point - the bits that follow are simply my opinions on the encroachment of “alternative technologies” in to established practices and these issues cannot be discussed with out causing offence to someone somewhere. Those of a nervous disposition or delicate nature read no further.


I am dangerously near my allotted three score and ten years on the planet and my initial reaction (a good number of years ago) to the use of synthetic O rings as piston rings was “Oh no! Not another new technology to master!”

It was the same with Loctite. I had been making press-fit interfaces for a couple of decades and then they introduce this idea of gluing stuff in place - what is the world coming to?

There is a thing called “progress” - I didn’t vote for it myself, we are just stuck with it.

I have a day job (retirement is for wimps) teaching engineering apprentices and lecturing in engineering. My last job in industry was as Head of Electronics at the European R and D centre of a global corporation that nobody has ever heard of. I spent my time working on time plans, spreadsheets, budgets, while in the labs just down the corridor talented engineers were doing the job I originally signed up for in my youth - hands on engineering research

I left industry when I accepted that if the brilliant young engineers leaving university and college did NOT have better ideas, better imaginations and better visions of the future than I had, then there is something very, very wrong with our education system.

So I teach my students to embrace the opportunities provided by exciting new technological developments, use CAD/CAM, 3D printing, CNC (or at least DROs) while in my hobby I still machine press-fits, turn by hand, and (to my lasting shame) know that I can file a part flat and true to with in a few thou in less time that it would take me to wrestle with the set-up of the part on my mill and rummage through a jumbled box of cutters in my disorganised home workshop. It is a case of “Do as I say, not as I do”

This means I now fall in to the category of “miserable old git”, I have my own chair in the corner of the pub where I can bang my fist on the table, moan about “young people” and start everything I say with the words “Well back in my day .....” (or at least I could do all of that before this virus thingy took off)

I’ll stop now - I have to “FaceTime” my sons so they can listen to me moan about the Six Nations (England has been at war with France for the last thousand years so it rankles to see them at the top of the table) and then we can get on to discuss the cricket umpiring in India....

Ah, gads, what a complainer! you know, the snow was whiter when I was a kid (last week). the Six Nations, BTW FYI IMNSHO, r the MOhauk, Iroquois, Huron, Seneca and I forgets the other two who made a peace instead of constantly warring against each other. Yeah, yeah, kidz, how will the humanity survive?

 

[Tim Wescott]

My question, which was sorta kinda touched on a bit above here, but only qualitatively, is how long will O-rings last vs. cast iron rings? In the event that I wanted to bolt it to a model airplane and go fly it, how many hours can I put on an O-ring engine vs. how many hours on a cast-iron ringed engine?

 

[Aerostar55]

Gentlemen,
I have been following the O ring discussion in another thread and have read several others in the past. Most of the builders on this forum have been machining and making engines for quite some time. That being said I have trouble understanding why there is such an aversion to making actual piston rings. If one follows the discussions about O ring use there seems to be more negatives than positives in their use. It seems everyone has their own guidelines for using them, type, O ring, X ring, material, Viton, neoprene, piston fit, loose, tight, cylinder wall fit, tight versus loose. When using piston rings there are hard numbers and data for their use. I feel that using O rings is taking the easy way out. Granted for a novice builder who would just like to build his first engine and hear it run I understand their thoughts but for the rest of us that have two or more engines under our belt I don't understand the aversion to making and using piston rings. Having built many engines over the years and following other's builds the biggest challenge in getting an engine running, bar none, is getting the valves to seat and seal properly. Hours can be spent machining the valves, seat cutting, lapping and pressure testing but yet we all accomplish this task one way or another. In building an engine there's so many somewhat complicated parts that need to be made, gears, cams, valves and crankshafts to name but a few and yet here again we are all able to do this but mention the word piston ring and some people get cold chills. To me making rings is one of the easier machining exercises connected with building an engine. You turn a piece of iron (very easy to machine) to a given I.D. and O.D. You then part it off to a given thickness. You break the edges then split the ring. If using the Trimble method a fixture needs to be made for heat treating. This is just another simple machining project. Now the heat treating. I don't have a kiln or heat treating furnace, I just use a standard propane torch. When making my fixture I hollow out the bottom so when heating there's not a lot of mass to heat up. Long ago i purchased a jar of Boron powder from a gun supply shop and after multitudes of piston rings I still have enough to last my engine building career. The rings are mounted on the fixture. The fixture is heated up then coated with the powder. The powder turns to a somewhat liquid coating much like silver solder flux. I then place the flame of the torch into the pocket in the bottom of the fixture so that I'm not applying the heat directly on the rings. I then hold the torch until the whole fixture and rings are brought up to a dull red color and once obtained hold it there for 2-3 minutes. The fixture is then allowed to cool and then the Boron coating is washed of with tap water. The rings are then unmounted, cleaned. fitted to the bore and gapped. Trimbles method and several other can be found on the internet for free and give a more thorough explanation in the making of piston rings.
To sum up my dissertation, why not give piston rings a try. It's really not that hard of a job and then you don't have to worry about all the issues of fitting and using O rings.
gbritnell

I agree, piston rings aren't that terribly difficult. I was once anxious to see my new project run so I just left the rings out ! After some success running, I went ahead and made some rings for it. NP (no problem)

 

[Aerostar55]

I recently made rings using the Trimble method. An interesting observation was that where I used celo-tape to hold the several wraps of heavy paper around the rings, the rings had no scale at all. The area that was covered with paper but had no tape the rings had some scale.

Mark T

I read the Strictly IC article "The Trimble Method" on piston ring, and its a great article. When I make rings I use a very similar method, but I cut out a couple of detailed steps. I never made the heat treating cup fixture. I just heat treat the rings on a steel plate in the vise. Also I use a slitting saw to cut the gap instead of the cleaver method. I find this saves filing time.

 

[popnrattle]

O-rings are the way to go for me cuz I like the easy way to do things, causes no wear on cyl., they last over a year and by that time it's ready to be taken apart to clean carbon and gunk from valves anyway. The hardest part for me is lapping the valves to seal well enough to run(half-hour or so). Here are my latest couple of examples. Later, RT.

 

[awake]

Hmmmm - - - - I, for one, would love to know that CAD/CAM, or even just CAD programs you use, recommend or whatever combination of that you care to offer.
3D printing - - - I'll start simple - - - - I would like to get such a system but - - - -which one?
Purchasing in north america drives the costs too high (imo) but purchasing in the far east significantly ups the risk.
Ideas, suggestions etc please.

ajoeiam, I missed this question earlier, and it looks like it didn't get answered, at least not on this thread.

There are several YouTube channels that focus on 3d printing, which include reviews. Two that I tend to trust the most are Tom Sanladerer and Maker's Muse. Based on their reviews, my sense is that for a basic machine, it is hard to beat the price & performance of the Ender 3, though they may require a little bit of tuning up (making sure the rollers and belts are properly tensioned). If you want to get rock-solid reliability, absolute best performance vs. price, it is hard to beat the Prusa - but now you're talking 4x the money.

Just to be clear, I have no stake in and no personal experience with either of these. My 3d printer is my own home-brewed design, based on commonly available components - it works very well, and at the time it saved some money compared to commercially available units. With the Ender 3 and similar machines, however, that last point is no longer true.

 

[ajoeiam]

ajoeiam, I missed this question earlier, and it looks like it didn't get answered, at least not on this thread.

There are several YouTube channels that focus on 3d printing, which include reviews. Two that I tend to trust the most are Tom Sanladerer and Maker's Muse. Based on their reviews, my sense is that for a basic machine, it is hard to beat the price & performance of the Ender 3, though they may require a little bit of tuning up (making sure the rollers and belts are properly tensioned). If you want to get rock-solid reliability, absolute best performance vs. price, it is hard to beat the Prusa - but now you're talking 4x the money.

Just to be clear, I have no stake in and no personal experience with either of these. My 3d printer is my own home-brewed design, based on commonly available components - it works very well, and at the time it saved some money compared to commercially available units. With the Ender 3 and similar machines, however, that last point is no longer true.

Why - - - thank you for your response sir!

If you might take a stab at the CAD and CAD/CAM question too please?

AISI CAM is quite necessary for 3D printing - - - - at least it would seem so. (grin)

 

[awake]

Sure, happy to address CAD and CAM for 3d printing:

A form of CAM is necessary, but in the 3d printing world, that is called a "slicer," and there are some excellent free & open source slicers available - I think the best is PrusaSlicer, but some people like Cura better. Either one will come with a large number of presets to suit different machines, but you can also adjust the parameters to suit your particular machine - that is what I have done with PrusaSlicer to use with my homebrew machine.

The slicer needs a 3d model file. The most common is an .stl file, which has the benefit of being near-universal. It also has the deficit of lacking any units of measurement - when it sees that something is "1" long, it doesn't know if that's 1 inch, 1mm, or 1 cubit. However, pretty much every system I know of defaults to mm as far as the .stl file and as far as what the 3d printer expects, even if the actual design is done in inches.

You don't actually have to do any CAD to start 3d printing. There are repositories with hundreds of thousands of .stl files that people have shared. Thingiverse is probably the best known such repository, but there are others. Just download the .stl file, slice it (feed it to PrusaSlicer or Cura, possibly scaling it as needed), and send the generated gcode to your printer.

If you want to create your own .stl file, then you do need some sort of 3d CAD system. A bit of searching on this forum will show you lots of discussion of the relative merits of different software, but in terms of software that is free to the hobbyist, the main choices (IMO) are Fusion 360, FreeCAD, or OpenSCAD. The latter two are free and open source; the former is a commercial package that has a somewhat limited free license for hobbyists.

Fusion 360 and FreeCAD both have enormous range of what they can do, and are suited for just about any design work - model up your parts, attach them together to see how it all fits, make up a set of technical drawings, generate g-code for a CNC mill, generate .stl files to print 3d models ... and the lists go on. They offer several different ways to build up a model (different ways may suit different problems), but the most common process for both is to start with a 2d sketch that is then "extruded" into a 3d part. From there, additional features are added or subtracted as needed, often by sketching the feature and creating an extrusion or a pocket, or by adding fillets or chamfers, or by repeating features across or around the part. (That may not make much sense without seeing it in action ....)

OpenSCAD is a very different approach, being essentially a programming script that tells the software how to put the model together. It is really only suited to creating .stl files for 3d printing, and not much of anything else - but there are times when it is the cat's meow for that purpose, and I often find myself choosing it for 3d printing designs. For the most part, this approach uses "constructive solid geometry," in which you tell it to create basic shapes such as cubes or spheres or cones or so on, then add these together or "subtract" one from another or take the intersection. (Again, hard to describe without actually seeing it in action ....)

Any of this software has some learning curve, but there are tons of tutorials. Just be aware that for FreeCAD and Fusion 360 in particular, you will usually want to limit yourself to more recently produced tutorials, because both programs continue to evolve - it is frustrating when the tutorial says to "click on this button," and that button no longer exists in the latest version.

 

[Kasey]

In a 2 stroke engine, is there any possibility that an O ring could replace the second ring and survive passing either the transfer or exhaust ports for very long? (even with a very tight fitting O ring on the piston)

 

[Brian Rupnow]

Where can I get a full explanation of the Trimble method of ring making, along with fixtures required? I have no plans for making another engine until fall, but I might try the Trimble method of making rings if I can find a good write up on it. I have tried the method of machining the rings to size, breaking a gap in the ring, and hanging them on a wedge and heating them until they dropped off.--I was not very successful with that. I have read about the Trimble method in the past, and have vague memories of needing two different fixtures. Any help would be appreciated.---Brian

 

[Tim Wescott]

http://modelenginenews.org/techniques/piston_rings.html

 

[jtb11711]

Brian,
Additionally, the George Trimble article referenced in the previously linked page is available for purchase from the Strictly IC website, for a price:
http://www.strictlyic.com/pit01.htm
John

[Edit: I should have known that my post would be delayed because it needed to be moderated, but there is the link if that is helpful.]

 

[AndrewW]

Where can I get a full explanation of the Trimble method of ring making, along with fixtures required? I have no plans for making another engine until fall, but I might try the Trimble method of making rings if I can find a good write up on it. I have tried the method of machining the rings to size, breaking a gap in the ring, and hanging them on a wedge and heating them until they dropped off.--I was not very successful with that. I have read about the Trimble method in the past, and have vague memories of needing two different fixtures. Any help would be appreciated.---Brian

Hi Brian
Strictly IC website suggests that they sell back issues. I enquired regarding the three issues featuring the Trimble method. Unfortunately Strictly IC said they only accept cheques or bank transfers in US$ which was too restrictive for me in the UK. A contact of mine in the US is in the process of trying to purchase them.
I've just made some piston rings based on your previous approach and they appear to have turned out well. Check my video out at:

Cheers
Andrew