O-Rings as piston rings

This Forum is dedicated to the Hobbyist I.C. (Internal Combustion) Engine Community.

Moderators: JackF, Harold_V

User avatar
tornitore45
Posts: 2077
Joined: Tue Apr 18, 2006 12:24 am
Location: USA Texas, Austin

O-Rings as piston rings

Post by tornitore45 »

All people that tried this had positive results, so I am going for it in my new Hoglet.

Question is how much interference from the true OD of the O-ring to the Bore?
I have no feeling for the friction to be expected in this case.
The O-ring catalog dimension are 1.004 x 0.864 x 0.070
Should the piston groove be 0.864 and let the ring compress radially?
OR
Should the groove be less than 0.864 and let the ring compress crcumferentially?

Am I overthinking the subject?

My wild guess is 0.001 on a 1" bore which should be mirror smooth
Mauro Gaetano
in Austin TX
User avatar
GlennW
Posts: 7284
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: O-Rings as piston rings

Post by GlennW »

According to my O-ring catalog:

Clearance between the piston and cylinder to be .005"

Groove diameter to be bore diameter minus .114"

Groove width to be .090"

This for a moving piston seal, but it does not specify if hydraulic or pneumatic.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
User avatar
tornitore45
Posts: 2077
Joined: Tue Apr 18, 2006 12:24 am
Location: USA Texas, Austin

Re: O-Rings as piston rings

Post by tornitore45 »

Thank you Glenn this give me something to work with

I suppose the catalog data is targeted to a slow moving application, like a faucet for example.
I feel with this dimensions the friction is too high for an IC engine application.

all in thousands
(140-114)/2=13 So the 70 section is compressed by 13 ~ 20% sounds like a lot
It appears like the ring is forced to reduce its circumference by 0.4% which is really a trifle, but is compressed from the inside.
This means that if the groove dimension, as given, result too shallow and yield too much friction, I can go back and deepen the groove.
Mauro Gaetano
in Austin TX
User avatar
warmstrong1955
Posts: 3568
Joined: Thu Mar 18, 2010 2:05 pm
Location: Northern Nevada

Re: O-Rings as piston rings

Post by warmstrong1955 »

Go here, and download the Parker O-Ring manual: https://www.parker.com/literature/ORD%2 ... ndbook.pdf
I would have just attached it, but it was too large for the boards.
This is the bible of o-ring design.
Read the 'dynamic' design section, and then you can go to the charts for all the dimensions you will need.

I did both hydraulic and pneumatic seal design, and I am a fan of back-up rings, most especially in dynamic designs. They improve o-ring life greatly, and prevent nibbling, which is a common o-ring failure. I have widened many a groove, to add a back-up.

Bill
Today's solutions are tomorrow's problems.
User avatar
GlennW
Posts: 7284
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: O-Rings as piston rings

Post by GlennW »

I doubt that you will find specific application data for what you are wanting to do, so most likely the "trial and error" method will come into play!

The info I posted is for a linear actuating cylinder with an O-ringed piston.

It seems to me the "real" Bill (seal killer) did a similar project and got it working using O-rings after some experimentation.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
User avatar
warmstrong1955
Posts: 3568
Joined: Thu Mar 18, 2010 2:05 pm
Location: Northern Nevada

Re: O-Rings as piston rings

Post by warmstrong1955 »

Not sure I recall correctly, but I think Bill's problem at first was seal drag. (friction) So Mauro's comment about 'deepening the groove', is a sound one.
So is improving the surface finish, improving lubrication, and using a higher durometer of o-ring, which will decrease the CoF.
I think I would just toward the 'loose' end (less squeeze) of the tolerance, since it is a low pressure application.

Other Bill
(not the Real Bill)
Today's solutions are tomorrow's problems.
User avatar
GlennW
Posts: 7284
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: O-Rings as piston rings

Post by GlennW »

warmstrong1955 wrote: Tue Jul 10, 2018 7:49 am Not sure I recall correctly, but I think Bill's problem at first was seal drag. (friction) So Mauro's comment about 'deepening the groove', is a sound one.
That is what I was referring to with the "trial and error" method.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
User avatar
warmstrong1955
Posts: 3568
Joined: Thu Mar 18, 2010 2:05 pm
Location: Northern Nevada

Re: O-Rings as piston rings

Post by warmstrong1955 »

GlennW wrote: Tue Jul 10, 2018 8:53 am
warmstrong1955 wrote: Tue Jul 10, 2018 7:49 am Not sure I recall correctly, but I think Bill's problem at first was seal drag. (friction) So Mauro's comment about 'deepening the groove', is a sound one.
That is what I was referring to with the "trial and error" method.
Yup! I was agreeing with you!
:)
Other Bill
Today's solutions are tomorrow's problems.
User avatar
GlennW
Posts: 7284
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: O-Rings as piston rings

Post by GlennW »

I'm not used to that. :)
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
User avatar
warmstrong1955
Posts: 3568
Joined: Thu Mar 18, 2010 2:05 pm
Location: Northern Nevada

Re: O-Rings as piston rings

Post by warmstrong1955 »

GlennW wrote: Tue Jul 10, 2018 10:36 am I'm not used to that. :)
No no.....Steve Graham is not used to that!
;)
Today's solutions are tomorrow's problems.
User avatar
tornitore45
Posts: 2077
Joined: Tue Apr 18, 2006 12:24 am
Location: USA Texas, Austin

Re: O-Rings as piston rings

Post by tornitore45 »

Many modeler have found the solution but I did not pay attention to the numeric details when reading about specific projects.
Unless someone that has successfully run a model engine comes up with the number I will start with a shallow groove and work from there until the piston friction feels the same as an engine with cast iron rings.
Mauro Gaetano
in Austin TX
User avatar
Harold_V
Posts: 20227
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: O-Rings as piston rings

Post by Harold_V »

tornitore45 wrote: Tue Jul 10, 2018 5:51 pm I will start with a shallow groove and work from there until the piston friction feels the same as an engine with cast iron rings.
I'm not sure that would work, as I suspect the coefficient of friction for an O ring is far greater than that of a well seated iron ring. Could be that by the time it felt "right" you'd be too loose and it would leak. Finish of the bore will be critical, especially in regards to ring life. A high polish would respond far differently from a rough honed surface, needless to say.

In any case, it's an interesting experiment. Be certain to post what you learn.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Post Reply