Using Rubber O rings for piston rings

[Roger U]

I am thinking of trying rubber O rings in place of cast iron piston rings, as i have not tried them before are standard O rings ok to use also is there any special tolerance requirements. How long are they expected to last before replacing them

regards Roger

[Marc P]

What's your bore? I have seen some on scale model engines that have worked. Viton o rings work longer but the bores are around an inch +/-. I would assume they would be less than great in bigger bores due to wearing out fast and any excessive clearance may blow them out and may need replaced often anyhow due to gas and oil deterioration.

[Kevin O. Pulver]

I think O-rings are supposed to be somewhat narrower than the grooves they ride in, so they can roll back and forth a bit. If you have to replace them a few times, real cast rings may be cheaper, but they might last a good while. I've only seen them used on models, but I bet it would work fine for quite a while if you're not building a lot of heat. Kevin

[OTTO-Sawyer]

I'm guessing you would also need the cylinders honed a lot smoother too to keep the O-rings from getting chewed up as opposed to needing the standard cross-hatch hone pattern for breaking in a set of rings.

[Case Place]

Rubber o-rings have their place of use; hydraulic cylinder pistons, slow moving; flange to flange seals, storage container caps and just about any static sealing application you can think of. O-ring seals are not for pistons that will be moving back and forth such as a gas and/or steam engine piston. As mentioned earlier the o-ring groove is slightly wider than the o-ring to be used. It tends to roll in order to make a better seal when used on a slow moving part.

Point in case, my father tried to use a teflon o-rings on a 1/2" diameter piston on his coke bottle style steam engine. No mater what he did it took over 20 pounds of air to to get the piston to move. It would stick at the far end of the stroke and was not a very smooth running engine. He tried to make his own piston ring out of teflon bar stock. Some improvements but still was not a very good running engine.

My suggestion, if it is a gas engine use the cast iron piston rings. If the size is impractical, then machine several oil grooves in the piston and mix oil with your gas. If it is a steam engine, use graphite impregnated yarn in a groove that is used for packing glands and valve stems. It works great. I have used it many times.

If you need really small piston rings, look to the model airplane engine suppliers. I have seen rings on engines with a 1/2" diameter or less. Good luck !

Grace and Peace, Larry

[Bill Feasal]

Pm Research inc use teflon rings in there steam engines, I built one of there models with a 1 inch bore and I can make it run with my lung power, but not for very long.

[Case Place]

Bill I am curious; have you tried steam yet. You will be amazed what heat will do to teflon.

I will have admit that dad made the little engine with some very tight tolerances. He seemed to think that the smaller the engine the tighter the tolerances. So many of his engines were so tight you could hardly turn them over by hand.

Anyway, thanks for the input, Larry

[Ken K]

I have used Viton, good to 450 degrees, X type o-rings, in hit miss engines for years, with good results. One 3/4" bore engine had over 50 hours on it, and the o-ring was still good.
Have not tried normal type o-rings, as the X o-rings, work so well.
If you have an "OPPS", and the bore is .010-.020" over size, you do not have a ring gap problem, with the X o-rings.
Ken K

[Forrest A]

O rings have been used for many years in lots of model engines with varying results. Here are some suggestions. Do not hone the cylinder; You want a smooth bore using O rings. Use O rings that are not affected by gasoline. When buying O rings buy several more than you need or think you will need as there are slight differences in size from one to the next which means one O ring my work and the next one may not. Allow for swelling as the O ring heats it will get bigger, even heat resistant ones will swell. Model engines with O rings typically will only be run for just a short time so keep that in mind when deciding how to seal the piston to the cylinder.

[Bill Feasal]

No steam yet, still working on a boiler. Trucking and Fishing are eating up my time, er maybe Fishing and trucking.

[qsmx440]

Originally Posted by OTTO-Sawyer

I'm guessing you would also need the cylinders honed a lot smoother too to keep the O-rings from getting chewed up as opposed to needing the standard cross-hatch hone pattern for breaking in a set of rings.

Otto I thought the same as you for years but the cross hatch pattern is to hold oil. Once the bore is smooth it will wear quickly with metal to metal contact.

[boz]

I'm looking at a Redwing parts list from PM research, it seems they use o rings as well as conventional rings. They call it an oil ring.

[boz]

Can someone explain what advantages, if any, o rings have in I.C. engines over the conventional cast rings ?

[Rex Wellendorf]

Hi,
Cost?
Rex

[J.B. Castagnos]

I've heard of people trying them in worn cylinders, I guess they would be more forgiving than CI rings, they will follow thw worn spots in an out of round cylinder, Ci wil tend to stay round and allow leakage. One of my friends tried it in a farm engine with poor results, wouldn't run for an hour. We sleeved the motor and he's much happier with it.

[Chuck Foster]

to use "o" rings in a model gas engine you have to machine the grooves for a proper fit. there is a formula to calculate the width and depth of the groove.
i have never used "o" rings in any of my model engines but i have several friends that have used them and all have had great results. the next engine i build i am going to use "o" rings.
they seam to have less drag than cast rings.
a good friend of mine has a small hit and miss engine called a little brother and it must have 1500 to 2000 hours of running on it and it still runs great.
if any one is interested i will get the formula for calculating the "o" ring grooves and post it here.

chuck

[Roger U]

Hi Chuck
I would be most interest in the formula for calculating the piston grooves when using O rings

regards Roger

[Gil Garceau]

The hit and miss engine in this video has a viton o-ring that the builder installed and it has never been replaced. The engine is at least 10 years old. In this video it is adjusted to run a hair too slow.

http://www.youtube.com/watch?v=KuB6Oe-Boec

I have some fine steam engine models that have brass pistons with only oil grooves cut in them and they work quite nicely although I will say none of these are required to do any meaningful work load.

[rataylor]

A fellow told me to hone the cylinder the same size as the o-ring. Use .005-.010 shallower groove in piston than cross section of o-ring to push ring against cyl. wall, and make the groove width .005-.010 wider than the cross-section(as stated in an earlier post)so the ring can "roll" slightly. The bore on my engine is 1.250 dia. and stroke is 1.813 in.(2.22 cu.in.) Aluminum piston in C.I.cylinder honed with Sunnen J95 stone(6 micro inch finish). We have tried to destroy the single o-ring with a load(until the alum. piston expanded and the engine seized, spitting on the head would boil it away) but after cooling had just as much compression. We were all impressed with the durability of the Viton. $0.72 cents each at the local hardware store. Cast iron rings are 5 bucks each. BTW, I use Coleman fuel with 40 to 1 ratio TC3w 2-cycle. You can see it do some work crushing cans on YT.

http://www.youtube.com/user/popnstart